Comparative brain gross morphology of the Neotropical catfish family Pseudopimelodidae (Osteichthyes, Ostariophysi, Siluriformes), with phylogenetic implications

Comparative brain gross morphology of the Neotropical catfish family Pseudopimelodidae... Abstract The Neotropical catfish family Pseudopimelodidae includes seven genera and 50 valid species, widely distributed in South America. To address the lack of comparative information on siluriform brains, the gross morphology of the major brain subdivisions of Pseudopimelodidae is described, illustrated and interpreted. A comprehensive comparison based on the shape, relative size and position of main brain subdivisions is presented for representative species of all valid genera in the family. Comparisons with species of other phylogenetically related families, Pimelodidae and Heptapteridae, and non-related species provide a broader context for understanding transformations in the pseudopimelodid brain. The phylogenetic implications of the observed modifications in the brain are discussed and new possible synapomorphies proposed. Using this new information, almost all genera were recovered as monophyletic using neuroanatomical characters. Additional morphological modification was hierarchically interpreted against previously proposed phylogenetic hypotheses. The results of this study provide further information with phylogenetic implications within Pseudopimelodidae and their position with respect to closely related families. evolution, freshwater, neural complex, phylogenetic systematics INTRODUCTION Time, evolution, the wide distribution of Siluriformes throughout diverse environments, and differences in behaviour could account for the considerable morphological variation found in catfishes. Such modifications have been detected, aside from osteology, in gas bladder and muscle anatomy (Bridge & Haddon, 1890, 1892, 1893; Sörensen, 1894, 1895; Howes, 1983; Diogo & Chardon, 2000; Diogo & Vandewalle, 2003; Diogo, Chardon & Vandewalle, 2004; Birindelli, Sousa & Sabaj-Perez, 2009; Datovo & Bockmann, 2010; Birindelli & Shibatta, 2011; Birindelli, Akama & Britski, 2012; Datovo & Vari, 2014). Despite the extensive literature concerning the anatomy of some morphological complexes, we still know little about the neuroanatomy of Siluriformes. Some research has been conducted on the central nervous systems of a few groups of non-siluriform teleosts (e.g. Evans, 1931; Eastman & Lannoo, 1995, 2001, 2007, 2008, 2011; Kotrschal, Van Staaden & Huber, 1998; Albert, Lannoo & Yuri, 1998; Albert, 2001; Ito et al., 2007), and several studies have adopted different approaches to the neuroanatomy of non-Neotropical species of the catfish family Ictaluridae (Finger, 1976; Knudsen, 1976; Lundberg, 1982; Tong & Finger, 1983; Meek & Nieuwenhuys, 1998; Striedter, 1991; Northcutt, Holmes & Albert, 2000). To date, few studies have been published on brain gross morphology in Neotropical Otophysi (Trajano, 1994; Albert et al., 1998; Albert, 2001; Rosa, Martins & Langeani, 2014; Abrahão & Shibatta, 2015; Pereira & Castro, 2016; Angulo & Langeani, 2017). The South American catfish family Pseudopimelodidae (sensuLundberg, Bornbusch & Mago-Leccia, 1991; Shibatta, 1998) is distributed on both sides of the Andean cordilleras, from the Atrato River in Colombia to the La Plata River in Argentina (Shibatta, 2003). This family comprises seven genera and ≥ 50 valid species (Eschmeyer, Fricke & van der Laan, 2017; Shibatta & Vari, 2017). Species assigned to the genera Cephalosilurus and Lophiosilurus have the largest body sizes [≤ 370 and 490 mm standard length (SL), respectively], but the vast majority of species are small to medium sized. Generally, the members of this family are omnivorous, feeding on aquatic insect larvae, allochthonous insects, fish and marginal vegetation. However, some species tend to be either carnivorous or even herbivorous (Shibatta, 1998; Esguícero & Arcifa, 2010). Details of their living habits are scarce, as they are difficult to capture. As a result, ichthyological collections often contain few specimens of these fishes. However, the available information indicates that Pseudopimelodidae are generally bottom dwellers of rivers and streams, hiding among roots, leaves, logs and rocks (Shibatta, 1998). Monophyly of Pseudopimelodidae is corroborated by a significant number of molecular (Sullivan, Lundberg & Hardman, 2006; Sullivan, Muriel-Cunha & Lundberg, 2013) and morphological (Lundberg et al., 1991; Shibatta & Vari, 2017) characters. Of the latter, the osteological features are particularly notable, as is common in Teleostei, where major groups are delimited by 74% of osteological synapomorphies (Wiley & Johnson, 2010; Datovo & Vari, 2014). The minor attention paid to other anatomical systems is derived from the lack of comparative studies, preventing a comprehensive assembly of data (Datovo & Vari, 2014). However, the amount of data on changes in vertebrate brains has resulted in considerable progress in the last 60 years (Northcutt, 1984, 1995; Wullimann & Northcutt, 1990; Striedter, 1991, 1992; Butler, 1994; Meek & Nieuwenhuys, 1998). Nevertheless, questions about what changes in brains subdivisions occurred, and whether these interpreted changes are phylogenetically applicable, are far from being addressed for specific groups. The functional diversity, shape and size of some neural structures have undergone amazing modifications over the course of evolution, rivalled by very few organs. The brain is responsible for sensory perception and processing and for behavioural responses (Nieuwenhuys, ten Donkelaar & Nicholson, 1998). The modifications in brain morphology may be linked to sensory orientation, cognitive potential and motor abilities (Evans, 1931, 1940). The association between ecological and behavioural demands moulded a vast number of individual variations, and therefore, these variations can be recovered in a phylogenetic context (Kotrschal et al., 1998). Building on the work of Abrahão & Shibatta (2015), this study provides a comprehensive investigation of the brain gross morphology of Pseudopimelodidae species. The main brain subdivisions and major efferent and afferent projections of cranial nerves of 20 species of all valid genera of Pseudopimelodidae are described, illustrated in detail and compared with the literature. Different relationship hypotheses are discussed. Several new putative synapomorphies are proposed for most genera based on new observations of brain gross morphology. Additionally, some behavioural and ecological aspects linked to brain gross morphology are briefly discussed. MATERIAL AND METHODS Taxonomy The examined taxa were represented by specimens of all genera of Pseudopimelodidae considered valid by Shibatta & Vari (2017). The current taxonomic status of the species cited here follows Eschmeyer & Fong (2017). Institutional abbreviations Examined materials are deposited in the following institutions and collections: INCIVA (IMCN), Instituto para la Investigación y la Preservación del Patrimonio Cultural y Natural del Valle del Cauca, Cali, Colombia; INPA, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil; LIRP, Laboratório de Ictiologia de Ribeirão Preto-USP, Ribeirão Preto, Brazil; MCP, Museu de Ciências e Tecnologia da Pontifícia Universidade Católica, Porto Alegre, Brazil; MZUEL, Museu de Zoologia da Universidade Estadual de Londrina, Londrina, Brazil; MZUSP, Museu de Zoologia da Universidade de São Paulo, São Paulo, Brazil; and ROM, Royal Ontario Museum, Toronto, ON, Canada. Material examined Only specimens for which the brain was dissected and examined are listed. Family Pseudopimelodidae Batrochoglanis melanurus: MZUEL 3670 (number of specimens 1: 51.16 mm SL). Batrochoglanis raninus: MZUEL 6035 (1: 76.7 mm SL); MZUSP 23407 (2: 51.4–76.6 mm SL). Batrochoglanis sp.: INPA 30268 (2: 23.2–23.8 mm SL). Batrochoglanis villosus: MZUEL 6037 (1: 143.2 mm SL). Cephalosilurus albomarginatus: ROM 61336 (1: 87.3 mm SL). Cephalosilurus apurensis: MZUEL 6493 (1: 195.6 mm SL). Cephalosilurus fowleri: MZUEL 6040 (1: 275.0 mm SL). Cruciglanis pacifici: INCIVA (IMCN) 113 (1: 142.4 mm SL). Lophiosilurus alexandri: MZUEL 5377 (1: 58.7 mm SL); MZUSP 96276 (1: 73.1 mm SL). Microglanis cibelae: MZUEL 6038 (1: 40.0 mm SL); MCP 21190 (1: 33.5 mm SL). Microglanis cottoides: MZUEL 6033 (30: 14.4–48.8 mm SL). Microglanis garavelloi: MZUEL 6058 (11: 28.8–60.2 mm SL). Microglanis secundus: INPA 5730 (2: 22.8–23.4 mm SL). Microglanis cf. poecilus: INPA 6828 (1: 20.9 mm SL); MZUSP 38230 (2: 21.3–29.0 mm SL). Pseudopimelodus bufonius: MZUEL 5744 (6: 97.8–118.2 mm SL). Pseudopimelodus charus: MZUEL 6488 (1: 138.6 mm SL). Pseudopimelodus mangurus: MZUEL 2795 (1: 175.7 mm SL); MZUSP 24449 (1: 80.0 mm SL). Rhyacoglanis seminiger: LIRP 8042 (1: 57.4 mm SL). Rhyacoglanis altiparanae: MZUEL 6034 (4: 39.2–44.1 mm SL). Rhyacoglanis sp.: MZUEL 6039 (2: 48.3–53.4 mm SL). Comparative material of other families of Siluriformes Diplomystes mesembrinus: MZUSP 62595 (1: 97.5 mm SL). Goeldiella eques: MZUEL 7417 (1: 57.1 mm SL). Helogenes marmaoratus: MZUSP 117655 (8: 14.4–55.9 mm SL). Heptapterus mustelinus: MZUEL 6487 (2: 55.7–66.1 mm SL). Ictalurus punctatus: MZUEL 6671 (3:78.8–82.3 mm SL). Nematogenys inermis: MZUSP 88522 (1: 65.1 mm SL). Noturus flavus: MZUSP 62603 (1: 86.6 mm SL). Pimelodella avanhandavae: MZUEL 1574 (3: 117.6–132.2 mm SL). Pimelodus maculatus: MZUEL 1343 (3: 181.7–243.2 mm SL). Rhamdia quelen: MZUEL 6036 (6: 187.4–222.4 mm SL). Steindachneridion parahybae: MZUEL 5231 (1: 262.4 mm SL). Zungaro zungaro: MZUEL 6044 (1: 158.8 mm SL; 1: 180.3 mm HL); MZUEL 6049 (1: 181.4 mm SL). Nomenclature and preparations To avoid damaging the subdivisions of the brain, efferent and afferent nerve fibres, braincase bones and head muscles during dissection, specimens were counterstained for bone and cartilage according to a modified version of the procedure described by Taylor & Van Dyke (1985), as suggested by Datovo & Bockmann (2010). Osteological nomenclature follows Weitzman (1962) and Shibatta (1998). The dissections were performed following Abrahão & Pupo (2014) and Abrahão & Shibatta (2015). Neuroanatomical nomenclature follows Meek & Nieuwenhuys (1998). Abbreviations of brain gross morphology regions also follow Meek & Nieuwenhuys (1998) and are shown in Figure 1. The lobe previously indicated as eminentia granularis by Abrahão & Shibatta (2015) has now been corrected and renamed as the lateral line lobe, in accordance with Meek & Nieuwenhuys (1998). Figure 1. View largeDownload slide Brain of the bumblebee catfish Pseudopimelodus mangurus MZUEL 2795, 75.68 mm standard length, in dorsal (A), lateral (B) and ventral (C) views. Scale bar = 2 mm. Figure 1. View largeDownload slide Brain of the bumblebee catfish Pseudopimelodus mangurus MZUEL 2795, 75.68 mm standard length, in dorsal (A), lateral (B) and ventral (C) views. Scale bar = 2 mm. Photographs were taken with a digital camera attached to a stereomicroscope. The brains were fully immersed in ethanol 70% (to a depth of ~1 mm over the surface tissue) to avoid possible refractive problems, according to White & Brown (2015). An ellipsoid model was used to determine the volume of each brain region (i.e. dorsal medulla (gustative lobes), corpus cerebelli, tectum opticum plus torus semicircularis, hypothalamus, hypophysis and telencephalon). This method assumes that each region has an idealized elliptical shape (Van Staaden et al., 1995; Huber et al., 1997; Wagner, 2003; Lisney & Collin, 2006; Pollen et al., 2007; Ullmann, Cowin & Collin, 2010; White & Brown 2015). Linear measurements were made based on standardized images of dorsal, lateral and ventral views, using tpsDig 2.10 software (Rohlf, 2010). Measurements of length and width were obtained from dorsal and ventral views, and the measurements of height from the lateral view. The length was determined with a line parallel to the central point on each lobe, extending along the boundary between the anterior and posterior portions. The width was determined with a perpendicular line that crossed the length line, also at the central point of each lobe, extending between the maximal limit of the anterior and posterior portions. Finally, the height was determined across the central point of each lobe as far as the maximal limit of the dorsal and ventral portions (Fig. 2). Linear measurement values were converted into volume (V) measurements using the following formula: V = ⅙πlwh (where l = length, w = width and h = height). Figure 2. View largeDownload slide Dorsal (A), lateral (B) and ventral (C) views of Pseudopimelodus bufonius MZUEL 5744, 118.17 mm standard length, showing the measurements (length, width and height) that were made for the six brain structures (Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; PG, pituitary gland; Tel, telencephalon; and TO+TS, tectum mesencephali plus torus semicircularis). See Material and methods section for further details. Scale bar = 2 mm. Figure 2. View largeDownload slide Dorsal (A), lateral (B) and ventral (C) views of Pseudopimelodus bufonius MZUEL 5744, 118.17 mm standard length, showing the measurements (length, width and height) that were made for the six brain structures (Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; PG, pituitary gland; Tel, telencephalon; and TO+TS, tectum mesencephali plus torus semicircularis). See Material and methods section for further details. Scale bar = 2 mm. For lobes with paired hemispheres (i.e. tectum mesencephali and telencephalon), only one hemisphere was measured, and the value obtained was doubled. The total volume of the brain was also obtained with the ellipsoid model formula. The length was determined as a line between the maximal anterior limit of telencephalon as far as the maximal posterior limit of the lobus vagi, in the dorsal view. The width was determined as a line between the maximal lateral limit of the tectum mesencephali, in the dorsal view. The height was determined as a line between the maximal dorsal limit of the corpus cerebelli to the maximal ventral limit of the hypothalamus, in the lateral view (Fig. 2). All volume values for each lobe were determined in proportion to the total volume of the brain (Table 1). Table 1. Morphometry of brain of Pseudopimelodidae species and comparative material examined Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Total volume of brain (BV) is in cubic millimetres; other data are expressed as percentages of BV. Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; N, number of specimens examined; PG, pituitary gland; Tel, telencephalon; TO+TS, tectum opticum plus torus semicircularis. View Large Table 1. Morphometry of brain of Pseudopimelodidae species and comparative material examined Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Total volume of brain (BV) is in cubic millimetres; other data are expressed as percentages of BV. Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; N, number of specimens examined; PG, pituitary gland; Tel, telencephalon; TO+TS, tectum opticum plus torus semicircularis. View Large Anatomical drawings were made using a pen tablet and were based on photographs and direct stereomicroscopic observations. The drawings were finalized using Photoshop CC and Illustrator CC (Adobe Systems, San Jose, CA, USA). MORPHOLOGICAL DESCRIPTIONS Rhombencephalon The medulla spinalis of teleosts can exhibit many modifications in length and shape, relative to body specializations (Meek & Nieuwenhuys, 1998). Their boundaries are not as sharp as those of other posterior regions of the brain, but these regions perform similar functions related to motor control and body regulation (Butler & Hodos, 2005). Topographically, this component of the brain is located posterior to the vagal lobe. The medulla spinalis is positioned above the parasphenoid and beneath the supraoccipital process, passing through all vertebrae in all species examined. The medulla spinalis is tubular and varies little in diameter over its length. The medulla oblongata region is located in the anterior portion of the myelencephalon, from the terminations of the medulla spinalis to the nervus vagus in the dorsal view (Fig. 1). The anterior portion of the medulla oblongata lies posterolaterally to the lobus vagi, positioned dorsal to parasphenoid–basioccipital suture and ventral to the supraoccipital process. In all species examined, the cross-section of medulla oblongata is rounded, with the anterior portion slightly larger than the posterior. This subdivision was not measured, because its boundaries are not readily apparent. In Siluriformes, the lobus vagi is generally a unilobate, non-laminated enlargement of the viscerosensory brainstem region, located in the intermedioventral rhombencephalic region (Meek & Nieuwenhuys, 1998), accommodating projections from the oropharyngeal branches of the nervus vagus (Morita & Finger, 1985). These efferent and afferent terminations provide gustatory, tactile and proprioceptive inputs from the oropharyngeal cavity (Kanwal & Caprio, 1983, 1987). The lobus vagi is positioned ventral to the posterior portion of supraoccipital process, located in the dorsal portion of the rhombencephalon, immediately posterior to the lobus facialis (Fig. 1). The branches of the nervus vagus has projections from the anterior portion of each lobe of the lobus vagi (Fig. 1). These projections, along with the nervus glossopharyngeus, exit the braincase through the foramen on the exoccipital. The V-shaped lobus vagi of all Pseudopimelodidae species examined has two cylindrical lobes, which come into contact only at their posterior portions, caudally forming an acute tip in the dorsal view (Figs 3–5). This tip forms an acute angle in the majority of the species examined, but forms a right angle in M. secundus. The proportional volume of the gustative lobes is higher than the proportional volume of the pituitary gland in all Pseudopimelodidae species examined (Table 1). Figure 3. View largeDownload slide A–C, brain gross morphology in dorsal view of: A, Cruciglanis pacifici MCP non-catalogued, 142.45 mm standard length (SL); B, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL; and C, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 3. View largeDownload slide A–C, brain gross morphology in dorsal view of: A, Cruciglanis pacifici MCP non-catalogued, 142.45 mm standard length (SL); B, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL; and C, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 4. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Cephalosilurus fowleri MZUEL 6040, 275.01 mm standard length (SL); and B, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 4. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Cephalosilurus fowleri MZUEL 6040, 275.01 mm standard length (SL); and B, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 5. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL); and B, Microglanis cottoides MZUEL 6033, 40.08 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 5. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL); and B, Microglanis cottoides MZUEL 6033, 40.08 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. The lobus facialis is an enlargement of the anterior portion of the nucleus of the tractus solitarius. It receives sensory inputs from the nervus facialis, which is connected to taste buds in the mouth cavity and on the lips and body surface. Within Teleostei, the largest and most diverse lobus facialis is found in Siluriformes (Meek & Nieuwenhuys, 1998), perhaps owing to the massed quantity of taste buds in the mouth cavity and barbels (Atema, 1971). The lobus facialis is located in the intermedioventral rhombencephalic region (Meek & Nieuwenhuys, 1998), positioned posterior to the corpus cerebelli, anterior to the lobus vagi, and medial to the lateral line lobe. This subdivision is located in the dorsal portion of the rhombencephalon, beneath the supraoccipital process (Fig. 1). In all Pseudopimelodidae species examined, the lobus facialis is adjacent and continuous to the lobus vagi and has two approximately rectangular, paired lobes, vertically oriented, with parallel medial margins usually in contact with each other. As an exception, in C. pacifici, this subdivision has two vertically oriented elliptical paired lobes. These lobes are usually positioned abreast in parallel and do not form an angle, but in Rhyacoglanis sp., the lobes of the lobus facialis are oriented diagonally, forming a right angle. In almost all Pseudopimelodidae species examined, the anterolateral portion above the lobes of the lobus facialis is covered in intumescences. However, in Cephalosilurus and Lophiosilurus, these bulges are on only the anterior portion of the lobus facialis (Figs 3–5). These structures in the transverse and sagittal planes result in four subdivisions, which are also formed by the lobus vagi and lateral line lobe, but in most instances do not come into contact with the corpus cerebelli. The posterior cerebellum encompasses the caudal lobe and the eminentia granularis. The latter consists of masses of granular cells, visible on the gross morphology of the brain (Meek & Nieuwenhuys, 1998). In Siluriformes, the eminentia granularis can be subdivided into two parts (medial and lateral), projecting respectively to the mechanoreceptors and the electrosensory lateral line regions (Tong & Finger, 1983). The eminentia granularis is located in the dorsal rhombencephalic region (Meek & Nieuwenhuys, 1998), anterolateral to the lobus facialis and posterior to the corpus cerebelli. In the neurocranium, the eminentia granularis is positioned beneath the supraoccipital process. Usually, there is no topographically visible division separating the corpus cerebelli and the eminentia granularis, nor the two portions of this structure. In all species examined, the lobes of the eminentia granularis are somewhat cylindrical in the dorsal view. In Siluriformes, the lateral line lobe is involved in mechano- and electrosensory stimulation and is referred to as both the medial nucleus (mechanical stimulation) and the lateral nucleus (electrical stimulation) (McCormick, 1982, 1992; Meek & Nieuwenhuys, 1998). We decided to use the general term lateral line lobe for this region, because similar terminology is used in the literature, and to avoid confusion regarding their boundaries. The lateral line lobe is located in the dorsal rhombencephalic region (Meek & Nieuwenhuys, 1998), beneath the supraoccipital process, near the suture between the pterotic and exoccipital processes (Fig. 1). It is posterolateral to the eminentia granularis and the corpus cerebelli, and lateral to the lobus facialis. Immediately below the anterior portion of this area, the rami of the nervus oculomotorius, trochlearis, trigeminus, abducens, facialis, octavus and linea lateralis anterior have projections that exit the braincase through the foramina on the pterosphenoid (Fig. 1). In almost all species examined, the lateral line lobe forms two conspicuous circular bulges with two subdivisions each (anterior and posterior). The anterior subdivision is larger than the posterior in all pseudopimelodids, except for Microglanis, which has only one circular bulge on each lateral line lobe (Figs 3–5). Usually, there is no topographically visible division separating the corpus cerebelli from the lateral line lobe, nor separating the two portions of this structure. Only C. pacifici exhibited a notch between the anterior and posterior subdivision of the lateral line lobe (Fig. 3C). The boundary of this structure differs between the species examined. In Rhyacoglanis, Batrochoglanis and Microglanis, the lateral line lobe extends to the boundary between the posterior portion of lobus facialis and the anterior portion of vagal lobe. However, in Cephalosilurus, Cruciglanis, Pseudopimelodus and Lophiosilurus, the lateral line lobe extends as far as the anterior portion of the lobus vagi (Figs 3–5). The teleostean corpus cerebelli is an unpaired protrusion on the dorsal surface of the hindbrain, a specialization located in the dorsalmost rhombencephalic region (Meek & Nieuwenhuys, 1998). This lobe is responsible for processing information from the lateral line, electrical signals, vestibular, somatosensory and auditory system signals (Finger, 1983). The corpus cerebelli is positioned immediately anterior to the lobus facialis, dorsal to the hypothalamus, and between the lobes of the tectum mesencephali (Fig. 1). In Cruciglanis, Pseudopimelodus and Rhyacoglanis, the anterior portion of this structure is positioned dorsal to the posterior area of the telencephalon. Therefore, in Batrochoglanis, Cephalosilurus, Lophiosilurus and Microglanis, the corpus cerebelli does not overlap with any portion of the telencephalon, which means that in some instances the habenula is visible (Figs 3–6). Figure 6. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in lateral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 5, lobus inferior hypothalami; 8, tectum mesencephalic; 9, corpus cerebelli; 10, lateral line lobe. Scale bars = 2 mm. Figure 6. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in lateral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 5, lobus inferior hypothalami; 8, tectum mesencephalic; 9, corpus cerebelli; 10, lateral line lobe. Scale bars = 2 mm. The corpus cerebelli had the most modifications in this study and can take several forms in the dorsal view. Geometrical shapes were used to denote the general morphologies of the corpus cerebelli. It is an ellipse in Cruciglanis and Pseudopimelodus, with the anterior and posterior portions rounded, and the posterior area slightly larger than the anterior. An oval shape is found in Rhyacoglanis, with both edges rounded, but the posterior portion is much wider than the anterior portion. Finally, in Batrochoglanis, Cephalosilurus, Lophiosilurus and Microglanis, the corpus cerebelli is triangle shaped, with the posterior portion rounded and wider than the anterior portion, which almost comes to a point (Figs 3–5). The posterior margin of the corpus cerebelli has two convex bulges in Batrochoglanis and Lophiosilurus. In Cruciglanis, Microglanis, Pseudopimelodus and Rhyacoglanis, it forms a single convex bulge, and in Cephalosilurus the posterior margin of the corpus cerebelli is straight. The anterior margin of the corpus cerebelli is rounded in all species of Pseudopimelodidae. The lateral margins of this structure are straight and anteriorly inclined. In Rhyacoglanis, the dorsal surface of the corpus cerebelli has a conspicuous longitudinal crest on the sagittal medial plane, with slight depressions on both parallel sides. In all the remaining species, this region has no noticeable undulations or ridges (Figs 3–5). In Batrochoglanis and Microglanis, the corpus cerebelli is wider than it is long. In Cruciglanis and Rhyacoglanis, the corpus cerebelli occupies the largest proportional volume of the Pseudopimelodidae brain (Table 1). In all the remaining species examined, the corpus cerebelli is only smaller than the telencephalon, but in Batrochoglanis it is also smaller than the hypothalamus (Table 1). The term ‘brainstem’ is often used in neuroanatomical papers and may refer to the ventralmost part of the brain except for any part of the diencephalon or, in fishes, include only the floor of the rhombencephalon (Nieuwenhuys & Pouwels, 1983; Butler & Hodos, 2005). We use the term truncus cerebri in an attempt to standardize the nomenclature used herein, and its boundaries are discriminated below. The truncus cerebri is located on the ventral surface of the brain and comprises the rhombencephalon and mesencephalon. More precisely, it extends from the posterior area of the chiasma opticum to the anterior area of the medulla spinalis and is located completely above the parasphenoid. Almost all cranial nerves exit from the truncus cerebri, except the nervus olfactorius and nervus opticus. The cranial nerves in this area include the oculomotor, trochlear, trigeminal, abducens, facial, octavus, glossopharyngeal, vagal, lateral line anterior and lateral line posterior (Fig. 1). No proportional length and shape modifications of the truncus cerebri were found in any of the pseudopimelodids (Fig. 7). Figure 7. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in ventral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus. Scale bars = 2 mm. Figure 7. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in ventral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus. Scale bars = 2 mm. Mesencephalon The tectum mesencephali is located in the dorsal portion of the tegmentum mesencephali, covering the generally large midbrain ventricle located in the dorsalmost portion of the mesencephalon (Meek & Nieuwenhuys, 1998). Topographically, it is positioned lateral to the corpus cerebelli in the dorsal view and posterior to the telencephalon (Fig. 1). The tectum mesencephali lobes are positioned beneath the supraoccipital process and frontal. These lobes are the main recipients of retinal stimuli through the nervus opticus (visual input processing) and are also involved in the integration of visual stimuli with sensory information from other regions, resulting in the generation and coordination of motor responses (Meek & Nieuwenhuys, 1998). In Cruciglanis, Pseudopimelodus and Rhyacoglanis, the medial margin of these lobes is located under the corpus cerebelli, whereas in Batrochoglanis, Cephalosilurus and Lophiosilurus, it is located under only the anterior portion, and in Microglanis the lobes extend further beyond the anterior margin of the corpus cerebelli. The tectum mesencephali has two bilaterally rounded structures in all species examined, in the lateral and dorsal views. In these species, the tectum mesencephali completely covers the torus semicircularis. However, in Batrochoglanis, Cephalosilurus, Lophiosilurus and Microglanis, the torus semicircularis is apparent below the tectum mesencephali. The proportional volume of the tectum mesencephali is smaller than that of the hypothalamus in all Pseudopimelodidae species examined, except for Lophiosilurus, in which the opposite is true (Table 1). The nervus opticus originates in the retina and emerges topographically from the ventralmost part of the tectum mesencephali on the mesencephalon. Its efferent and afferent projections exit in the region immediately anterior to the lobus inferior hypothalami, where their fibres cross the midline of the brain around the chiasma opticum (Figs 1, 7). These fibres come into contact with each other at the base of the chiasma opticum. The projections of the nervus opticus exit the braincase through a foramen located between the frontal, orbitosphenoid and pterosphenoid. The chiasma opticum is located ventral to the preoptic area, anterior to the hypothalamus, anteromedial to the lateral preglomerular nucleus, and over the parasphenoid. In Cephalosilurus and Lophiosilurus, the nervous tractus olfactorius is thicker than the optic nerve. This relationship is inverted in Cruciglanis, Microglanis and Pseudopimelodus. In Batrochoglanis, both nerves are of approximately the same thickness. Diencephalon The teleostean hypothalamus can be subdivided into three major regions: periventricular zone, tuberal region, and inferior hypothalamic lobes (Meek & Nieuwenhuys, 1998). This region receives inputs from the rhombencephalon, mesencephalon, hypophysis and telencephalon (Kanwal, Finger & Caprio, 1988; Striedter, 1990; Wulliman & Meyer, 1990; Lamb & Caprio, 1993). The hypothalamus is located in the ventralmost part of the diencephalon, anteromedial to the hypothalamic inferior lobes. It is semicircular, with straight medial portions (Fig. 7). The pituitary gland (or hypophysis) is circular and anchored medially to the posterior portion of the hypothalamus by the pituitary stalk, which contains hypothalamic and preoptic nerve fibres involved in neuroendocrine functions (Meek & Nieuwenhuys, 1998). No proportional length and shape modifications in the pituitary gland were found in any of the Pseudopimelodidae species examined. The saccus vasculosus, a rounded, darkish structure, is located posterior to the pituitary gland. This structure is also anchored over the hypothalamus and is approximately the same size as the pituitary gland (Figs 1, 7). The lobus inferior hypothalami is located lateroposterior to the tuberal hypothalamic region. These lobes comprise the distal part of the lateral recessus, the central nucleus and the nucleus diffusus lobi lateralis. It is the largest part of the hypothalamic region in teleostean fish and receives signals from gustatory centres, the suprachiasmatic nucleus and the ventral area of the telencephalon (Kanwal et al., 1988; Striedter, 1990; Finger & Kanwal, 1992; Lamb & Caprio, 1993; Meek & Nieuwenhuys, 1998). The lobus inferior hypothalami is positioned posterior to the chiasma opticum, ventral to the truncus cerebri and tectum mesencephali, and posterior to the telencephalon. These lobes are semicircular, with the anterior portion being slightly smaller than the posterior (Fig. 1). In Pseudopimelodidae, there are some undulations and ridges on the lateral margin of these lobes. No general shape modifications were found in the lobus inferior hypothalami (Fig. 7). The lateral preglomerular nucleus is a large protrusion in the lateral surface of the brain that can also be seen in the ventral view. This lobe is involved in toral, diencephalic and telencephalic connections (Striedter, 1992). The lateral preglomerular nucleus is located anterior to the lobus inferior hypothalami, anterolateral to the hypothalamus and above the tectum mesencephali, in the lateral view. The lobes of the lateral preglomerular nucleus are rounded in all species examined (Figs 1, 6, 7). The proportional volume of the hypothalamus was determined by grouping all subdivisions of the diencephalon area. In all species examined, the proportional volume of the hypothalamus was larger than that of the tectum mesencephali, except in Lophiosilurus. In Batrochoglanis, the proportional volume of the hypothalamus is larger than that of the corpus cerebelli (Table 1). Telencephalon The telencephalon is the rostralmost subdivision of teleostean brains and comprises an area dorsalis, an area ventralis and the bulbus olfactorius (Meek & Nieuwenhuys, 1998). The area dorsalis can be subdivided further into four cytoarchitectonic areas and the area ventralis into five cytoarchitectonic areas (Meek & Nieuwenhuys, 1998), but these subdivisions were not examined. Some studies have pointed out that the dorsal area receives a series of inputs from all main regions of the brain (Finger, 1980; Kanwal et al., 1988; Resink et al., 1989; Striedter, 1991, 1992) and that the ventral area receives inputs from the bulbus olfactorius (Finger, 1975; Bass, 1981; Resink et al., 1989). The telencephalon is also involved in learning, memory, gustation and some behavioural responses (de Bruin, 1980; Finger, 1980; Savage, 1980; Kanwal et al., 1988; Lamb & Caprio, 1993; Saito & Watanabe, 2006). The telencephalon is located anterior to the tectum mesencephali, posterior to the bulbus olfactorius, and its posterior area is positioned beneath the corpus cerebelli in many species (Figs 1–6). In all species examined, the telencephalon is connected to the bulbus olfactorius by a long tract (tractus olfactorius). The telencephalon is positioned beneath the frontal and supraoccipital processes. In all species examined, the telencephalon is longitudinally elongated and somewhat cylindrical, with rounded anterior and posterior margins. Many modifications in this structure were observed from in pseudopimelodids. Although no morphological patterns were found within Pseudopimelodidae, the modifications observed here might be of interest for future studies. The posterior portion of the telencephalon is smaller than the anterior portion in B. villosus, C. apurensis, C. fowleri, P. charus and P. mangurus. In C. pacifici, M. cibelae, M. cottoides, M. garavelloi and P. bufonius, both anterior and posterior portions are the same size and maintain the same width over their length. In Batrochoglanis sp., B. raninus, B. melanurus, C. albomarginatus, L. alexandri, M. poecilus, M. secundus and Rhyacoglanis, the anterior portion is smaller than the posterior portion (Figs 3–6). In most instances, the proportional volume of this subdivision is the largest in the brain. In Cruciglanis and Rhyacoglanis, however, the proportional volume of the telencephalon is smaller than that of the corpus cerebelli (Table 1). The bulbus olfactorius receives sensory inputs from nerve cells in the olfactory epithelium via the nervus olfactorius (Meek & Nieuwenhuys, 1998). The bulbus olfactorius is located beneath the nasal bone, near the articulation between the lateral ethmoid and the vomer. This structure in all pseudopimelodids is stalked, connected to the olfactory epithelium via the nervus olfactorius and connected to the telencephalon by a long tractus olfactorius. The anterior and posterior portions of the bulbus olfactorius are rounded and fairly elliptical. No proportional length and some shape modifications in the bulbus olfactorius were found in pseudopimelodids. In general, all species examined have a rounded olfactory epithelium, with the anterior edge slightly smaller than the posterior, laterally curved with numerous lamellae on each side, like a feather (Fig. 8). Figure 8. View largeDownload slide Olfactory organ of species of Pseudopimelodidae in dorsal view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici INCIVA non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. Scale bars = 1 mm. Figure 8. View largeDownload slide Olfactory organ of species of Pseudopimelodidae in dorsal view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici INCIVA non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. Scale bars = 1 mm. PHYLOGENETIC IMPLICATIONS Fink & Fink (1996) summarized a series of neural features to support the close relationship between the catfish and the electric knifefish. Details of these features are given by Albert et al. (1998) and Albert (2001). However, there is still no exhaustive knowledge of neuroanatomy for most Siluriformes, with no characters to support this clade (Wiley & Johnson, 2010). Despite the view that neural evolution involves a mosaic of functional and developmental processes (Northcutt, 1992; Striedter, 1992; Albert et al., 1998; Gonzalez-Voyer, Winberg & Kolm, 2009), patterns might be incorporated in evolutionary interpretations (Eastman & Lannoo, 1998; Albert, 2001; Di Dario & de Pinna, 2006; de Pinna, Ferraris & Vari, 2007; Rosa et al., 2014; Abrahão & Shibatta, 2015). Studies on fish nervous systems are still needed to elucidate fully the evolutionary processes involved. Brain gross morphology varies greatly in Pseudopimelodidae. There are considerable differences in the shape and size of the main subdivisions. Furthermore, a few intraspecific modifications were observed in some subdivisions. These intraspecific modifications are more conspicuous in the telencephalon, with the anterior portion sometimes being more bulged and larger than the posterior portion, but also sometimes not bulged and smaller. However, these features were not considered informative characters because of the considerable variation in lobe format in the specimens examined. The combination of considerable interspecific modification and restricted intraspecific variation suggests that brain gross morphology provides putative characters for the resolution of supraspecific groups. In addition, the morphological patterns shared by species within these groups are indicative of the fact that these characters might be useful in phylogenetic analyses. Notwithstanding their putative conservativeness, optimization of the proposed characters can highlight differences, if analysed with respect to existing hypotheses. Pimelodoidea The brain gross morphology of Pseudopimelodidae species examined is similar to closely related families in the superfamily Pimelodoidea, a clade well corroborated on the basis of molecular (Hardman, 2005; Sullivan et al., 2006, 2013) and morphological (Lundberg et al., 1991; Bockmann, 1998; Bockmann & Guazzelli, 2003; Britto, 2003; Lundberg & Littmann, 2003; Shibatta, 2003; Birindelli & Shibatta, 2011) characters, as follows: the lobus vagi composed of two cylindrical, paired, V-shaped lobes; lateral line lobe consisting of two conspicuous bulges, oval in shape, with the anterior portion more prominent than the posterior portion; and olfactory epithelium with numerous lamellae. As evidenced in the Heptapteridae species examined, the pituitary gland is displaced towards the medial region of the hypothalamus; the anterior portion of the lobus vagi is bulged; the intumescence on the lobus facialis is displaced towards the lateral portion; the lateral line lobe has two conspicuous bulges with no notch between them; the dorsal surface of the corpus cerebelli has no conspicuous crest; the corpus cerebelli is trapezoidal, extending upward less than half length of the telencephalon; and the corpus cerebelli is longer than the telencephalon. In the Pimelodidae species examined, the pituitary gland is displaced towards the posterior region of the hypothalamus; the anterior portion of the lobus vagi is bulged; the intumescence on the lobus facialis is displaced towards the anterolateral portion; the lateral line lobe has two conspicuous bulges with no notch between them; the dorsal surface of the corpus cerebelli has no conspicuous crest; the corpus cerebelli is rectangular, extending up to more than half length of the telencephalon; and the corpus cerebelli is greater in length than the telencephalon. Until recently, Pseudopimelodidae was recognized as belonging to the family Pimelodidae. The monophyly of the three subfamilies that made up Pimelodidae (Pimelodinae, Pseudopimelodinae and Heptapterinae) was proposed by Lundberg & McDade (1986) and Lundberg et al. (1988, 1991). This hypothesis gave rise to discussions regarding the phylogenetic position of the family. Pseudopimelodinae was considered a sister group of Heptapterinae (= Heptapteridae), based on the lip structure (Lundberg et al., 1988, 1991). Later, in a comprehensive phylogenetic analysis of Siluriformes, de Pinna (1993, 1998) considered Pseudopimelodinae as related to a clade consisting of Sisoroidea, Amphiliidae and Loricarioidea; Heptapterinae was included in a subgroup of Bagridae, and Pimelodinae was placed in a distal position as another subgroup of Bagridae. The close relationships between Pseudopimelodidae, Pimelodidae and Heptapteridae, placing them in a clade that also included Doradoidei and other groups, was recovered by Britto (2003). The families Pseudopimelodidae and Heptapteridae occupied the basal position in this clade. Using myology data, Diogo (2004) and Diogo et al. (2004) proposed that Pseudopimelodidae was a sister group to a clade formed by Pimelodidae and Heptapteridae. The molecular data recovered Pseudopimelodidae as a sister group of Pimelodidae, and the clade as a sister group of Heptapteridae plus Conorhynchos (Hardman, 2005; Sullivan et al., 2006). Most recently, a molecular-based study using nuclear and mitochondrial sequences provided strong support for the monophyly of the Pimelodoidea clade (Sullivan et al., 2013) formed by {[Conorhynchos plus Heptapteridae] [Pimelodidae (Pseudopimelodidae plus Phreatobius)]}. The similar structure of the constrictor muscle of the gas bladder in Pimelodidae and Pseudopimelodidae (Birindelli & Shibatta, 2011) was used as evidence for the sister group relationship between Pimelodidae and Pseudopimelodidae. The molecular studies of Sullivan et al. (2013) arrived at the same relationship scheme. Shibatta & Vari (2017), using morphological data, disagreed with that hypothesis. Data from neuroanatomical features was congruent with the first two hypotheses (Fig. 9). Based on the material examined herein, pseudopimelodids and pimelodids share three features of the encephalon, with Heptapteridae as sister to them. The first [1] is the position of the intumescence on the lobus facialis, which is oriented along the entire lateral margin on each lobe, in examined Heptapteridae species. Each lobe appears to have two regions longitudinally subdivided into two equal halves. In most Pseudopimelodidae and Pimelodidae species, this intumescence is located along the anterolateral portion. It occupies half the width of each lobe in the posterior portion and extends to the anteromedial portion (Figs 3–5, 10). A second possible synapomorphy for Pimelodidae plus Pseudopimelodidae is [2] the prolongation of the posterior portion of the lateral line lobe. In Heptapteridae, this region ends abruptly and reaches only half the length of the lateral margin of the lobus facialis. This condition is not found in Pimelodidae and most Pseudopimelodidae species (Figs 3–5, 10). In the material examined from these families, this posterior portion has a tail-shaped prolongation that extends up to the division between the lobus facialis and lobus vagi. The last possible synapomorphy for these two families is [3] the size of the saccus vasculosus. This structure can appear and disappear among teleosts. In Siluriformes, this diencephalic structure is characterized as well developed and moderately developed in most families. In Heptapteridae, the saccus vasculosus is smaller than the pituitary gland. However, in all the species of Pimelodidae and Pseudopimelodidae examined, this relationship is inverted, and the saccus vasculosus is the same length or longer than its anterior structure, the pituitary gland (Figs 7, 10). The independent and congruent signals provided by molecular and morphological data from the gas bladder and encephalon indicate that Heptapteridae is possibly the sister group of a clade with Pimelodidae and Pseudopimelodidae. Figure 9. View largeDownload slide Maximum parsimony optimization of the identified derived characters of the gross morphology of the brain superimposed on the cladogram of Pseudopimelodidae proposed by Shibatta & Vari (2017). Characters are numbered as described in the main text. Characters in green are putative synapomorphies for groups. Characters in red are homoplastic optimizations. Figure 9. View largeDownload slide Maximum parsimony optimization of the identified derived characters of the gross morphology of the brain superimposed on the cladogram of Pseudopimelodidae proposed by Shibatta & Vari (2017). Characters are numbered as described in the main text. Characters in green are putative synapomorphies for groups. Characters in red are homoplastic optimizations. Figure 10. View largeDownload slide Brain gross morphology of species of the outgroup in dorsal, lateral and ventral views, from left to right. A, Steindachneridion parahybae MZUEL 5231, 262.41 mm standard length (SL). B, Goeldiella eques MZUEL 7417, 57.1 mm SL. C, Diplomystes mesembrinus MZUSP 62595, 97.5 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 10. View largeDownload slide Brain gross morphology of species of the outgroup in dorsal, lateral and ventral views, from left to right. A, Steindachneridion parahybae MZUEL 5231, 262.41 mm standard length (SL). B, Goeldiella eques MZUEL 7417, 57.1 mm SL. C, Diplomystes mesembrinus MZUSP 62595, 97.5 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Pseudopimelodidae The monophyly of Pseudopimelodidae has been supported to date with morphological data by Lundberg et al. (1991), Shibatta (1998) and Shibatta & Vari (2017), and by Sullivan et al. (2013) with molecular data. In all species examined here, each lobe of the lobus vagi comes into contact posteriorally, forming an acute tip in the dorsal view. At least one derived condition of the lobus vagi in Pseudopimelodidae can be a putative synapomorphy for the family: [4] the absence of a conspicuous bulge on the anterior portion of this lobe (Figs 3–5, 9, 10). This lobe has anterior and posterior portions of the same width, in the dorsal view. Similar arrangements are observed only in some phylogenetically non-related groups (Pupo, 2015). In the examined species of Heptapteridae and Pimelodidae, this region has a conspicuous bulge on the anterior portion of the lobus vagi (Figs 3–5, 10). The previous analyses by Ortega-Lara & Lehmann (2006) presented the hypothesis that Pseudopimelodidae is composed of two major clades: the first with Pseudopimelodus, Cruciglanis, Batrochoglanis and Microglanis; and the second with Cephalosilurus and Lophiosilurus. This relationship scheme disagrees with the conclusions of Shibatta & Vari (2017). In this later study, Pseudopimelodidae is also composed of two major clades, but with some important differences: the first grouping is Pseudopimelodus, Cruciglanis and Rhyacoglanis; and the second is Cephalosilurus, Lophiosilurus, Batrochoglanis and Microglanis. Data from the brain are more congruent with this later hypothesis (Fig. 9). Based on the material examined, Cephalosilurus, Lophiosilurus, Batrochoglanis and Microglanis share two notable derived features. The first [5] is the general shape of the corpus cerebelli, somewhat triangular, with the posterior margin straight and much larger than the anterior margin, which can be rounded or at an acute angle (Figs 4, 5). The second [6] is the prolongation of the anterior portion of the corpus cerebelli, which extends as far as the boundary between the mesencephalon and the telencephalon but does not come into contact with the latter, exhibiting the habenula in the dorsal portion of the diencephalon (Figs 4, 5). In turn, Pseudopimelodus, Cruciglanis and Rhyacoglanis share one derived feature: the prolongation of the anterior portion of the corpus cerebelli [6] extends beyond the mesencephalon, but by less than half the length of the telencephalon (Fig. 3). Cephalosilurus and Lophiosilurus species share two features: an anterior intumescence on the lobus facialis [1] and the smaller size of this lobe [7] (Fig. 9). The intumescence is located only in the anterior portion on the lobes of the lobus facialis. In this conformation, the intumescence extends over the entire width of the anterior portion, dividing each lobe horizontally by two-thirds (Fig. 4). The extension of the lobus facialis comprises a half medial margin of the lateral line lobe. This feature is easily visible, projecting before the posterior portion of the lateral line lobe (Fig. 4). This close relationship is corroborated in all existing hypotheses (Ortega-Lara & Lehmann, 2006; Shibatta & Vari, 2017). In addition, species of Batrochoglanis and Microglanis also share two possible synapomorphies: the general format of the corpus cerebelli [8]; and the shorter length of the corpus cerebelli compared with the telencephalon [9] (Fig. 9). The corpus cerebelli is usually elongated sagitally in most Siluriformes. In most species examined, the corpus cerebelli is longer than its posterior width. However, in Batrochoglanis and Microglanis, this relationship is inverted. The corpus cerebelli is the most elongated subdivision of the brain in most species of Siluriformes. However, in the species of Batrochoglanis and Microglanis, the corpus cerebelli is decreased. In these genera, the telencephalon is longer than the corpus cerebelli and all other brain subdivisions (Fig. 5). These two genera were also closely related in the phylogenetic analysis proposed by Ortega-Lara & Lehmann (2006) and Shibatta & Vari (2017). The proposal formulated by Ortega-Lara & Lehmann (2006), that Pseudopimelodus is the sister group of a clade composed of Cruciglanis plus Batrochoglanis and Microglanis, disagrees with the hypothesis proposed by Shibatta & Vari (2017). In the latter, Pseudopimelodus is sister to Cruciglanis, and this clade is sister to Rhyacoglanis. Data from the brain are more congruent with this hypothesis (Fig. 9). Based on the material examined, Pseudopimelodus and Cruciglanis share two putative synapomorphies: the prolongation of the posterior portion of the lateral line lobe [2]; and the general shape of the corpus cerebelli [5]. The posterior portion of the lateral line in these species is extended until the anterior portion of the lobus vagi (Fig. 3). This derived condition is not found in other any species examined. In Pseudopimelodus and Cruciglanis, the anterior and posterior margins of the corpus cerebelli are equally rounded and somewhat elliptical (Fig. 3). Brain gross morphology data are consistent with the hypothesis of Shibatta (1998) and Shibatta & Vari (2017) of a monophyletic clade formed by Rhyacoglanis (Fig. 9). The corpus cerebelli in all these species is the same shape and has a conspicuous crest on the dorsal surface [10]. This crest is formed by depressions in the parasagittal plane. In these species, the crest is sagittally positioned along almost the entire length of the dorsal surface of the corpus cerebelli (Figs 3–5, 10). The remaining species examined herein do not have this crest. Therefore, this exclusive feature can be a possible synapomorphy for this genus. This group also has the coloration and body morphological features that differentiate it from the remaining pseudopimelodids (Shibatta, 1998; Shibatta & Vari, 2017). Likewise, the brain characters of Microglanis are consistent with the hypothesis of monophyly, with the lateral line lobe consisting of only one bulge, without any clear separation in the middle [11]. This derived condition is found only in other families of Siluriformes. Diplomystidae and other related groups have this condition, therefore, are possible synapomorphies for this genus (Fig. 5). In the remaining species of Pseudopimelodidae, the lateral line lobe has a clear separation located approximately in the middle of the structure. Where this separation into two bulges is found, the anterior bulge always protrudes further than the posterior one (Figs 3–5, 10). In addition, the volume of the corpus cerebelli compared with the volume of the hypothalamus is a character that supports the monophyly of Batrochoglanis. In these species, the hypothalamus is more robust and occupies a wide area in the ventral region of the brain (Table 1). The other species of Heptapteridae and Ictaluridae examined as comparative material have the same relationship between these two subdivisions [12]. Lastly, C. pacifici has a conspicuous notch between the anterior and posterior bulges of the lateral line lobe [13], a further autapomorphy for this monotypic genus. The monophyly of these last three genera was determined by Ortega-Lara & Lehmann (2006) and Shibatta & Vari (2017) (Fig. 9). ECOLOGICAL AND BEHAVIOURAL NOTES A comparison among all examined species of Pseudopimelodidae presented differences in the volume of the major subdivisions of the brain, which may be associated with their behavioural and ecological characteristics. These associations have been empirically tested by many authors and have proved to be realistic, principally when focusing on closely related groups (Evans, 1940; Ridet & Bauchot, 1990; Eastman & Lannoo, 1995; van Staaden et al., 1995; Kotrschal et al., 1998). Furthermore, the modifications in the size of brain subdivisions are reliable predictors of their relative importance (Kishida, 1979; Kotrschal & Palzenberger, 1992; Kotrschal et al., 1998). Within Otophysi (sensuWiley & Johnson, 2010) and in relationship to the other groups, Characiformes and Gymnotiformes (e.g. Albert, 2001; Pereira & Castro, 2016), Cypriniformes and Siluriformes have well-developed gustative lobes, with elaborate external taste and tactile systems (Marui, 1977; Marui & Caprio, 1982; Marui et al., 1988; Angulo & Langeani, 2017). The species of Pseudopimelodidae follow the same pattern; the lobus vagi and the lobus facialis are developed and occupy a broad area in the dorsal region of the rhombencephalon. The majority of Pseudopimelodidae species can be categorized as omnivorous or carnivorous, feeding on allochthonous insects, algae, vegetal debris and fishes (Shibatta, 1998). In accordance with Shibatta’s observations, there are no great variations in volume of the gustative lobe region in all specimens examined (Table 1), evidencing similar feeding behaviour. Although the corpus cerebelli is the largest subdivision in various groups of Otophysi (Brandstätter & Kotrschal, 1990; Albert, 2001; Ching, Senoo & Kawamura, 2015; Pereira & Castro, 2016; Angulo & Langeani, 2017), in Pseudopimelodidae the sizing varies between genera. At one end of this spectrum are species of Pseudopimelodus, with the largest and most voluminous corpus cerebelli (Table 1). Larger corpus cerebelli may be linked to increased motor control while swimming in structurally complex environments (Bauchot et al., 1989; Kotrschal et al., 1998). This theory is in accordance with observations on the habitat and distribution of these species. These species inhabit the main channels of rivers, with strong rapids and rocky bottoms (Shibatta, 1998). At the other extreme, species of Microglanis and Batrochoglanis have the smallest and least voluminous corpus cerebelli (Table 1). These results may also be related to their habitat and distribution, because they are commonly found in riparian vegetation, hidden among the roots of macrophytes, with weaker rapids (Oscar A. Shibatta, personal observation). The dorsal region of the mesencephalon is more voluminous in Lophiosilurus (Table 1). According to Shibatta (1998), this species is not active and is an ambush predator, buried in the sand. The increase of this subdivision may be related to visual acuity, despite other functions related to this region (i.e. Huber et al., 1997; Wagner, 2003). All remaining species are active predators, swimming among rocks, trunks and roots to hunt their prey. Our results suggest that the size of brain subdivisions in species of Pseudopimelodidae varies with feeding behaviour and preferred environment. However, these associations are based only on empirical data from a series of other studies with other groups of fishes, as cited above. Therefore, despite the logic of these associations, empirical analyses are needed. Although comparative neurobiologists have made advances in establishing when and in what ways brain morphology has changed, there has been little progress in understanding how and why such changes have occurred. This is, in part, attributable to a lack of studies focused on comparative neuroanatomy. Research on ontogenetic transformations should be used to understand changes over time and to provide robust information on the mechanisms for change. Finally, an interdisciplinary approach that includes anatomy, physiology, ethology, ontogeny and phylogeny is required to understand these mechanisms (Northcutt, 2002). This study is the first step towards comprehending what changes occurred in Pseudopimelodidae brains, with some speculation on when these modifications occurred, based on recent phylogenetic hypotheses. New research on Siluriformes should test these assumptions in brain evolution. ACKNOWLEDGEMENTS The authors are grateful to Luiz Peixoto and Gustavo Ballen (MZUSP) for reading and commenting on the manuscript. We thank Mario de Pinna (MZUSP), Ricardo Castro (LIRP), Lucia Py Daniel (INPA), Luiz Malabarba (MCP), Pablo Lehmann (MCP), Francisco Provenzano (MBUCV), Mary Burridge (ROM) and Germán Parra (INCIVA-IMCN) for the loan of specimens and permission to dissect them. This project had the logistical support of Edson Santana (UEL) in collections and laboratorial issues, and Silvia Ponzoni (UEL) for assistance in the physiological laboratory. The authors are extremely grateful to two anonymous reviewers and to Louise Allcock, the editor of this journal. The careful and constructive comments certainly benefited the paper. O.A.S. is a research fellow of the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico/process 304868/2015-9). 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Comparative brain gross morphology of the Neotropical catfish family Pseudopimelodidae (Osteichthyes, Ostariophysi, Siluriformes), with phylogenetic implications

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Oxford University Press
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© 2018 The Linnean Society of London, Zoological Journal of the Linnean Society
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0024-4082
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1096-3642
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10.1093/zoolinnean/zly011
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Abstract

Abstract The Neotropical catfish family Pseudopimelodidae includes seven genera and 50 valid species, widely distributed in South America. To address the lack of comparative information on siluriform brains, the gross morphology of the major brain subdivisions of Pseudopimelodidae is described, illustrated and interpreted. A comprehensive comparison based on the shape, relative size and position of main brain subdivisions is presented for representative species of all valid genera in the family. Comparisons with species of other phylogenetically related families, Pimelodidae and Heptapteridae, and non-related species provide a broader context for understanding transformations in the pseudopimelodid brain. The phylogenetic implications of the observed modifications in the brain are discussed and new possible synapomorphies proposed. Using this new information, almost all genera were recovered as monophyletic using neuroanatomical characters. Additional morphological modification was hierarchically interpreted against previously proposed phylogenetic hypotheses. The results of this study provide further information with phylogenetic implications within Pseudopimelodidae and their position with respect to closely related families. evolution, freshwater, neural complex, phylogenetic systematics INTRODUCTION Time, evolution, the wide distribution of Siluriformes throughout diverse environments, and differences in behaviour could account for the considerable morphological variation found in catfishes. Such modifications have been detected, aside from osteology, in gas bladder and muscle anatomy (Bridge & Haddon, 1890, 1892, 1893; Sörensen, 1894, 1895; Howes, 1983; Diogo & Chardon, 2000; Diogo & Vandewalle, 2003; Diogo, Chardon & Vandewalle, 2004; Birindelli, Sousa & Sabaj-Perez, 2009; Datovo & Bockmann, 2010; Birindelli & Shibatta, 2011; Birindelli, Akama & Britski, 2012; Datovo & Vari, 2014). Despite the extensive literature concerning the anatomy of some morphological complexes, we still know little about the neuroanatomy of Siluriformes. Some research has been conducted on the central nervous systems of a few groups of non-siluriform teleosts (e.g. Evans, 1931; Eastman & Lannoo, 1995, 2001, 2007, 2008, 2011; Kotrschal, Van Staaden & Huber, 1998; Albert, Lannoo & Yuri, 1998; Albert, 2001; Ito et al., 2007), and several studies have adopted different approaches to the neuroanatomy of non-Neotropical species of the catfish family Ictaluridae (Finger, 1976; Knudsen, 1976; Lundberg, 1982; Tong & Finger, 1983; Meek & Nieuwenhuys, 1998; Striedter, 1991; Northcutt, Holmes & Albert, 2000). To date, few studies have been published on brain gross morphology in Neotropical Otophysi (Trajano, 1994; Albert et al., 1998; Albert, 2001; Rosa, Martins & Langeani, 2014; Abrahão & Shibatta, 2015; Pereira & Castro, 2016; Angulo & Langeani, 2017). The South American catfish family Pseudopimelodidae (sensuLundberg, Bornbusch & Mago-Leccia, 1991; Shibatta, 1998) is distributed on both sides of the Andean cordilleras, from the Atrato River in Colombia to the La Plata River in Argentina (Shibatta, 2003). This family comprises seven genera and ≥ 50 valid species (Eschmeyer, Fricke & van der Laan, 2017; Shibatta & Vari, 2017). Species assigned to the genera Cephalosilurus and Lophiosilurus have the largest body sizes [≤ 370 and 490 mm standard length (SL), respectively], but the vast majority of species are small to medium sized. Generally, the members of this family are omnivorous, feeding on aquatic insect larvae, allochthonous insects, fish and marginal vegetation. However, some species tend to be either carnivorous or even herbivorous (Shibatta, 1998; Esguícero & Arcifa, 2010). Details of their living habits are scarce, as they are difficult to capture. As a result, ichthyological collections often contain few specimens of these fishes. However, the available information indicates that Pseudopimelodidae are generally bottom dwellers of rivers and streams, hiding among roots, leaves, logs and rocks (Shibatta, 1998). Monophyly of Pseudopimelodidae is corroborated by a significant number of molecular (Sullivan, Lundberg & Hardman, 2006; Sullivan, Muriel-Cunha & Lundberg, 2013) and morphological (Lundberg et al., 1991; Shibatta & Vari, 2017) characters. Of the latter, the osteological features are particularly notable, as is common in Teleostei, where major groups are delimited by 74% of osteological synapomorphies (Wiley & Johnson, 2010; Datovo & Vari, 2014). The minor attention paid to other anatomical systems is derived from the lack of comparative studies, preventing a comprehensive assembly of data (Datovo & Vari, 2014). However, the amount of data on changes in vertebrate brains has resulted in considerable progress in the last 60 years (Northcutt, 1984, 1995; Wullimann & Northcutt, 1990; Striedter, 1991, 1992; Butler, 1994; Meek & Nieuwenhuys, 1998). Nevertheless, questions about what changes in brains subdivisions occurred, and whether these interpreted changes are phylogenetically applicable, are far from being addressed for specific groups. The functional diversity, shape and size of some neural structures have undergone amazing modifications over the course of evolution, rivalled by very few organs. The brain is responsible for sensory perception and processing and for behavioural responses (Nieuwenhuys, ten Donkelaar & Nicholson, 1998). The modifications in brain morphology may be linked to sensory orientation, cognitive potential and motor abilities (Evans, 1931, 1940). The association between ecological and behavioural demands moulded a vast number of individual variations, and therefore, these variations can be recovered in a phylogenetic context (Kotrschal et al., 1998). Building on the work of Abrahão & Shibatta (2015), this study provides a comprehensive investigation of the brain gross morphology of Pseudopimelodidae species. The main brain subdivisions and major efferent and afferent projections of cranial nerves of 20 species of all valid genera of Pseudopimelodidae are described, illustrated in detail and compared with the literature. Different relationship hypotheses are discussed. Several new putative synapomorphies are proposed for most genera based on new observations of brain gross morphology. Additionally, some behavioural and ecological aspects linked to brain gross morphology are briefly discussed. MATERIAL AND METHODS Taxonomy The examined taxa were represented by specimens of all genera of Pseudopimelodidae considered valid by Shibatta & Vari (2017). The current taxonomic status of the species cited here follows Eschmeyer & Fong (2017). Institutional abbreviations Examined materials are deposited in the following institutions and collections: INCIVA (IMCN), Instituto para la Investigación y la Preservación del Patrimonio Cultural y Natural del Valle del Cauca, Cali, Colombia; INPA, Instituto Nacional de Pesquisas da Amazônia, Manaus, Brazil; LIRP, Laboratório de Ictiologia de Ribeirão Preto-USP, Ribeirão Preto, Brazil; MCP, Museu de Ciências e Tecnologia da Pontifícia Universidade Católica, Porto Alegre, Brazil; MZUEL, Museu de Zoologia da Universidade Estadual de Londrina, Londrina, Brazil; MZUSP, Museu de Zoologia da Universidade de São Paulo, São Paulo, Brazil; and ROM, Royal Ontario Museum, Toronto, ON, Canada. Material examined Only specimens for which the brain was dissected and examined are listed. Family Pseudopimelodidae Batrochoglanis melanurus: MZUEL 3670 (number of specimens 1: 51.16 mm SL). Batrochoglanis raninus: MZUEL 6035 (1: 76.7 mm SL); MZUSP 23407 (2: 51.4–76.6 mm SL). Batrochoglanis sp.: INPA 30268 (2: 23.2–23.8 mm SL). Batrochoglanis villosus: MZUEL 6037 (1: 143.2 mm SL). Cephalosilurus albomarginatus: ROM 61336 (1: 87.3 mm SL). Cephalosilurus apurensis: MZUEL 6493 (1: 195.6 mm SL). Cephalosilurus fowleri: MZUEL 6040 (1: 275.0 mm SL). Cruciglanis pacifici: INCIVA (IMCN) 113 (1: 142.4 mm SL). Lophiosilurus alexandri: MZUEL 5377 (1: 58.7 mm SL); MZUSP 96276 (1: 73.1 mm SL). Microglanis cibelae: MZUEL 6038 (1: 40.0 mm SL); MCP 21190 (1: 33.5 mm SL). Microglanis cottoides: MZUEL 6033 (30: 14.4–48.8 mm SL). Microglanis garavelloi: MZUEL 6058 (11: 28.8–60.2 mm SL). Microglanis secundus: INPA 5730 (2: 22.8–23.4 mm SL). Microglanis cf. poecilus: INPA 6828 (1: 20.9 mm SL); MZUSP 38230 (2: 21.3–29.0 mm SL). Pseudopimelodus bufonius: MZUEL 5744 (6: 97.8–118.2 mm SL). Pseudopimelodus charus: MZUEL 6488 (1: 138.6 mm SL). Pseudopimelodus mangurus: MZUEL 2795 (1: 175.7 mm SL); MZUSP 24449 (1: 80.0 mm SL). Rhyacoglanis seminiger: LIRP 8042 (1: 57.4 mm SL). Rhyacoglanis altiparanae: MZUEL 6034 (4: 39.2–44.1 mm SL). Rhyacoglanis sp.: MZUEL 6039 (2: 48.3–53.4 mm SL). Comparative material of other families of Siluriformes Diplomystes mesembrinus: MZUSP 62595 (1: 97.5 mm SL). Goeldiella eques: MZUEL 7417 (1: 57.1 mm SL). Helogenes marmaoratus: MZUSP 117655 (8: 14.4–55.9 mm SL). Heptapterus mustelinus: MZUEL 6487 (2: 55.7–66.1 mm SL). Ictalurus punctatus: MZUEL 6671 (3:78.8–82.3 mm SL). Nematogenys inermis: MZUSP 88522 (1: 65.1 mm SL). Noturus flavus: MZUSP 62603 (1: 86.6 mm SL). Pimelodella avanhandavae: MZUEL 1574 (3: 117.6–132.2 mm SL). Pimelodus maculatus: MZUEL 1343 (3: 181.7–243.2 mm SL). Rhamdia quelen: MZUEL 6036 (6: 187.4–222.4 mm SL). Steindachneridion parahybae: MZUEL 5231 (1: 262.4 mm SL). Zungaro zungaro: MZUEL 6044 (1: 158.8 mm SL; 1: 180.3 mm HL); MZUEL 6049 (1: 181.4 mm SL). Nomenclature and preparations To avoid damaging the subdivisions of the brain, efferent and afferent nerve fibres, braincase bones and head muscles during dissection, specimens were counterstained for bone and cartilage according to a modified version of the procedure described by Taylor & Van Dyke (1985), as suggested by Datovo & Bockmann (2010). Osteological nomenclature follows Weitzman (1962) and Shibatta (1998). The dissections were performed following Abrahão & Pupo (2014) and Abrahão & Shibatta (2015). Neuroanatomical nomenclature follows Meek & Nieuwenhuys (1998). Abbreviations of brain gross morphology regions also follow Meek & Nieuwenhuys (1998) and are shown in Figure 1. The lobe previously indicated as eminentia granularis by Abrahão & Shibatta (2015) has now been corrected and renamed as the lateral line lobe, in accordance with Meek & Nieuwenhuys (1998). Figure 1. View largeDownload slide Brain of the bumblebee catfish Pseudopimelodus mangurus MZUEL 2795, 75.68 mm standard length, in dorsal (A), lateral (B) and ventral (C) views. Scale bar = 2 mm. Figure 1. View largeDownload slide Brain of the bumblebee catfish Pseudopimelodus mangurus MZUEL 2795, 75.68 mm standard length, in dorsal (A), lateral (B) and ventral (C) views. Scale bar = 2 mm. Photographs were taken with a digital camera attached to a stereomicroscope. The brains were fully immersed in ethanol 70% (to a depth of ~1 mm over the surface tissue) to avoid possible refractive problems, according to White & Brown (2015). An ellipsoid model was used to determine the volume of each brain region (i.e. dorsal medulla (gustative lobes), corpus cerebelli, tectum opticum plus torus semicircularis, hypothalamus, hypophysis and telencephalon). This method assumes that each region has an idealized elliptical shape (Van Staaden et al., 1995; Huber et al., 1997; Wagner, 2003; Lisney & Collin, 2006; Pollen et al., 2007; Ullmann, Cowin & Collin, 2010; White & Brown 2015). Linear measurements were made based on standardized images of dorsal, lateral and ventral views, using tpsDig 2.10 software (Rohlf, 2010). Measurements of length and width were obtained from dorsal and ventral views, and the measurements of height from the lateral view. The length was determined with a line parallel to the central point on each lobe, extending along the boundary between the anterior and posterior portions. The width was determined with a perpendicular line that crossed the length line, also at the central point of each lobe, extending between the maximal limit of the anterior and posterior portions. Finally, the height was determined across the central point of each lobe as far as the maximal limit of the dorsal and ventral portions (Fig. 2). Linear measurement values were converted into volume (V) measurements using the following formula: V = ⅙πlwh (where l = length, w = width and h = height). Figure 2. View largeDownload slide Dorsal (A), lateral (B) and ventral (C) views of Pseudopimelodus bufonius MZUEL 5744, 118.17 mm standard length, showing the measurements (length, width and height) that were made for the six brain structures (Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; PG, pituitary gland; Tel, telencephalon; and TO+TS, tectum mesencephali plus torus semicircularis). See Material and methods section for further details. Scale bar = 2 mm. Figure 2. View largeDownload slide Dorsal (A), lateral (B) and ventral (C) views of Pseudopimelodus bufonius MZUEL 5744, 118.17 mm standard length, showing the measurements (length, width and height) that were made for the six brain structures (Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; PG, pituitary gland; Tel, telencephalon; and TO+TS, tectum mesencephali plus torus semicircularis). See Material and methods section for further details. Scale bar = 2 mm. For lobes with paired hemispheres (i.e. tectum mesencephali and telencephalon), only one hemisphere was measured, and the value obtained was doubled. The total volume of the brain was also obtained with the ellipsoid model formula. The length was determined as a line between the maximal anterior limit of telencephalon as far as the maximal posterior limit of the lobus vagi, in the dorsal view. The width was determined as a line between the maximal lateral limit of the tectum mesencephali, in the dorsal view. The height was determined as a line between the maximal dorsal limit of the corpus cerebelli to the maximal ventral limit of the hypothalamus, in the lateral view (Fig. 2). All volume values for each lobe were determined in proportion to the total volume of the brain (Table 1). Table 1. Morphometry of brain of Pseudopimelodidae species and comparative material examined Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Total volume of brain (BV) is in cubic millimetres; other data are expressed as percentages of BV. Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; N, number of specimens examined; PG, pituitary gland; Tel, telencephalon; TO+TS, tectum opticum plus torus semicircularis. View Large Table 1. Morphometry of brain of Pseudopimelodidae species and comparative material examined Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Taxa N BV GL Cereb TO+TS HI PG Tel Volume (mm3) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Volume (mm3) Volume (%) Diplomystes mesembrinus 1 101.5 2.94 2.8 19.1 18.8 10.8 10.6 5.4 5.3 0.1 0.1 8.6 8.5 Ictalurus punctatus 3 58.8–61.9 1.73–1.79 2.9 4.4–4.6 7.4 7–7.2 11.6–11.9 4.5–4.7 7.6 0.1 0.2–0.3 5.7–5.9 9.5–9.6 Heptapterus mustelinus 2 34.6–35.4 1.42–1.48 4.1 2.5–2.6 7.2–7.5 2.6–2.7 7.5–7.7 2.8–2.9 8–8.3 0.05–0.06 0.1 2.8–2.9 8–8.3 Pimelodella avanhandavae 3 176.4–182.1 4.33–4.41 2.4 14.6–14.8 8.1–8.2 13.5–13.6 7.4–7.6 9.2–9.4 5.1–5.2 0.2 0.1 15.9–16.4 9 Rhamdia quelen 6 475.1–487 14.3–15.5 3–3.1 35.4–36.7 7.4–7.5 26.5–27.8 5.5–5.7 33.2–34.1 6.9–7 1.4–1.6 0.2–0.3 38.7–40.4 8.1–8.3 Pimelodus maculatus 3 627.3–633.4 24.3–26 3.8–4.1 68.9–71.1 10.9–11.2 36.9–37.3 5.8 39.3–40.9 6.2–6.4 1.1–1.2 0.1 39.6–40 6.3 Zungaro zungaro 1 368.6 7.9 2.1 59.8 16.2 20.1 5.4 36.1 9.8 1.1 0.3 36.3 9.8 Steindachneridion parahybae 1 651.6 19 2.9 90.1 13.8 36.3 5.5 49 7.5 1.2 0.1 52.3 8 Rhyacoglanis altiparanae 4 22.8–23.6 1–1.1 4.3–5 2.2–2.3 9.6–10 1.5–1.6 6.5–6.9 1.9–2.1 8.3–8.9 0.06–0.08 0.2–0.3 3.1–3.2 13.5–13.6 Rhyacoglanis seminiger 1 31.2 1.2 3.9 3.3 10.5 2.2 7.1 3.2 10.4 0.08 0.2 2.8 9.1 Rhyacoglanis sp. 2 29.8–30.1 1.1–1.2 3.6–3.9 3.2 10.6–10.7 2.1–2.2 7–7.3 3–3.1 10–10.2 0.08–0.09 0.2 3–3.1 10–10.2 Pseudopimelodus bufonius 6 81.2–83.2 2.4–2.5 2.9–3 9.8–10.1 12–12.1 2.6–2.9 3.2–3.5 5.8–6 7.1–7.2 0.2 0.2 12.9–13.5 15.8–16.2 Pseudopimelodus charus 1 88.7 3.1 3.4 10.6 11.9 3 3.3 6.4 7.2 0.2 0.2 12.5 14 Pseudopimelodus mangurus 2 79.8–233.3 3.2–9.7 4–4.1 12.6–40 15.7–17.1 2.2–6.7 2.7–2.8 6.1–19.6 7.6–8.4 0.2–0.7 0.2–0.3 10.6–29.1 12.4–13.2 Cruciglanis pacifici 1 62.1 2 3.3 8.1 13 2.3 3.8 7 11.3 0.3 0.4 6.4 10.4 Batrochoglanis melanurus 1 23.8 0.7 3.3 1.5 6.2 1.5 6.5 2.4 10.1 0.04 0.1 3.1 13 Batrochoglanis villosus 1 81.8 3.9 4.7 7.2 8.8 3.4 4.2 6.1 7.5 0.2 0.3 11 13.5 Batrochoglanis raninus 3 24.8–30.1 0.9–1.1 3.6 1.6–2 6.4–6.7 1.4–1.7 5.6–5.7 1.9–2.3 7.6–7.8 0.1–0.2 0.4–0.6 2.8–3.5 11.2–11.6 Batrochoglanis sp. 2 19.8 0.6–0.7 3–3.5 1.2–1.3 6–6.5 0.9–1 4.5–5 1.4–1.5 7–7.5 0.03–0.05 0.1–0.2 2.5–2.6 12.6–13.1 Microglanis cibelae 2 20.9–21.3 0.6–0.7 2.8–3.2 1.9–2.1 9–9.8 1.6–1.7 7.6–7.9 1.7–1.8 8.1–8.4 0.1 0.4 2.3–2.4 11–11.2 Microglanis cottoides 3 21.2–21.4 0.5–0.9 2.3–4.4 2.1–2.2 9.9–10.2 1.3–1.4 6.2–6.6 1.8–1.9 8.4–8.9 0.1 0.4 2.4 11.2–11.3 Microglanis garavelloi 11 7.3–21.2 0.3–0.6 2.8–4.1 0.7–2.1 9.9 0.6–1.6 7.5–8.2 0.6–1.8 8.4–8.6 0.03–0.1 0.4 0.9–2.4 11.3–12.3 Microglanis poecilus 3 7.2–8.9 0.3–0.4 4.1–4.4 0.7–0.8 8.9–9.7 0.6 6.7–8.3 0.6–0.8 8.3–8.9 0.03–0.04 0.4 0.8–1 11.1–11.2 Microglanis secundus 2 6.8–7.4 0.3 4–4.4 0.6–0.7 8.8–9.4 0.5 6.7–7.3 0.6 8.1–8.8 0.03 0.4 0.8–0.9 11.7–12.1 Cephalosilurus albomarginatus 1 27.3 1 3.6 2.4 8.7 1.3 4.7 1.6 5.8 0.1 0.3 3.2 11.7 Cephalosilurus apurensis 1 124 4.5 3.6 10.5 8.5 5 4 11.9 9.6 0.3 0.2 15 12.1 Cephalosilurus fowleri 1 227.3 7.4 3.2 21.3 9.4 10.5 4.6 13 5.7 1.5 0.6 25.8 11.3 Lophiosilurus alexandri 2 44.7–46.8 1.4–1.5 3.1–3.2 4–4.2 8.9–9.1 3.6 7.7 2.6 5.7 0.1 0.2 4.5 9.7 Total volume of brain (BV) is in cubic millimetres; other data are expressed as percentages of BV. Cereb, corpus cerebelli; GL, gustative lobes; HI, hypothalamus; N, number of specimens examined; PG, pituitary gland; Tel, telencephalon; TO+TS, tectum opticum plus torus semicircularis. View Large Anatomical drawings were made using a pen tablet and were based on photographs and direct stereomicroscopic observations. The drawings were finalized using Photoshop CC and Illustrator CC (Adobe Systems, San Jose, CA, USA). MORPHOLOGICAL DESCRIPTIONS Rhombencephalon The medulla spinalis of teleosts can exhibit many modifications in length and shape, relative to body specializations (Meek & Nieuwenhuys, 1998). Their boundaries are not as sharp as those of other posterior regions of the brain, but these regions perform similar functions related to motor control and body regulation (Butler & Hodos, 2005). Topographically, this component of the brain is located posterior to the vagal lobe. The medulla spinalis is positioned above the parasphenoid and beneath the supraoccipital process, passing through all vertebrae in all species examined. The medulla spinalis is tubular and varies little in diameter over its length. The medulla oblongata region is located in the anterior portion of the myelencephalon, from the terminations of the medulla spinalis to the nervus vagus in the dorsal view (Fig. 1). The anterior portion of the medulla oblongata lies posterolaterally to the lobus vagi, positioned dorsal to parasphenoid–basioccipital suture and ventral to the supraoccipital process. In all species examined, the cross-section of medulla oblongata is rounded, with the anterior portion slightly larger than the posterior. This subdivision was not measured, because its boundaries are not readily apparent. In Siluriformes, the lobus vagi is generally a unilobate, non-laminated enlargement of the viscerosensory brainstem region, located in the intermedioventral rhombencephalic region (Meek & Nieuwenhuys, 1998), accommodating projections from the oropharyngeal branches of the nervus vagus (Morita & Finger, 1985). These efferent and afferent terminations provide gustatory, tactile and proprioceptive inputs from the oropharyngeal cavity (Kanwal & Caprio, 1983, 1987). The lobus vagi is positioned ventral to the posterior portion of supraoccipital process, located in the dorsal portion of the rhombencephalon, immediately posterior to the lobus facialis (Fig. 1). The branches of the nervus vagus has projections from the anterior portion of each lobe of the lobus vagi (Fig. 1). These projections, along with the nervus glossopharyngeus, exit the braincase through the foramen on the exoccipital. The V-shaped lobus vagi of all Pseudopimelodidae species examined has two cylindrical lobes, which come into contact only at their posterior portions, caudally forming an acute tip in the dorsal view (Figs 3–5). This tip forms an acute angle in the majority of the species examined, but forms a right angle in M. secundus. The proportional volume of the gustative lobes is higher than the proportional volume of the pituitary gland in all Pseudopimelodidae species examined (Table 1). Figure 3. View largeDownload slide A–C, brain gross morphology in dorsal view of: A, Cruciglanis pacifici MCP non-catalogued, 142.45 mm standard length (SL); B, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL; and C, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 3. View largeDownload slide A–C, brain gross morphology in dorsal view of: A, Cruciglanis pacifici MCP non-catalogued, 142.45 mm standard length (SL); B, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL; and C, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 4. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Cephalosilurus fowleri MZUEL 6040, 275.01 mm standard length (SL); and B, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 4. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Cephalosilurus fowleri MZUEL 6040, 275.01 mm standard length (SL); and B, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 5. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL); and B, Microglanis cottoides MZUEL 6033, 40.08 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 5. View largeDownload slide A, B, brain gross morphology in dorsal view of: A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL); and B, Microglanis cottoides MZUEL 6033, 40.08 mm SL. 1, telencephalon; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. The lobus facialis is an enlargement of the anterior portion of the nucleus of the tractus solitarius. It receives sensory inputs from the nervus facialis, which is connected to taste buds in the mouth cavity and on the lips and body surface. Within Teleostei, the largest and most diverse lobus facialis is found in Siluriformes (Meek & Nieuwenhuys, 1998), perhaps owing to the massed quantity of taste buds in the mouth cavity and barbels (Atema, 1971). The lobus facialis is located in the intermedioventral rhombencephalic region (Meek & Nieuwenhuys, 1998), positioned posterior to the corpus cerebelli, anterior to the lobus vagi, and medial to the lateral line lobe. This subdivision is located in the dorsal portion of the rhombencephalon, beneath the supraoccipital process (Fig. 1). In all Pseudopimelodidae species examined, the lobus facialis is adjacent and continuous to the lobus vagi and has two approximately rectangular, paired lobes, vertically oriented, with parallel medial margins usually in contact with each other. As an exception, in C. pacifici, this subdivision has two vertically oriented elliptical paired lobes. These lobes are usually positioned abreast in parallel and do not form an angle, but in Rhyacoglanis sp., the lobes of the lobus facialis are oriented diagonally, forming a right angle. In almost all Pseudopimelodidae species examined, the anterolateral portion above the lobes of the lobus facialis is covered in intumescences. However, in Cephalosilurus and Lophiosilurus, these bulges are on only the anterior portion of the lobus facialis (Figs 3–5). These structures in the transverse and sagittal planes result in four subdivisions, which are also formed by the lobus vagi and lateral line lobe, but in most instances do not come into contact with the corpus cerebelli. The posterior cerebellum encompasses the caudal lobe and the eminentia granularis. The latter consists of masses of granular cells, visible on the gross morphology of the brain (Meek & Nieuwenhuys, 1998). In Siluriformes, the eminentia granularis can be subdivided into two parts (medial and lateral), projecting respectively to the mechanoreceptors and the electrosensory lateral line regions (Tong & Finger, 1983). The eminentia granularis is located in the dorsal rhombencephalic region (Meek & Nieuwenhuys, 1998), anterolateral to the lobus facialis and posterior to the corpus cerebelli. In the neurocranium, the eminentia granularis is positioned beneath the supraoccipital process. Usually, there is no topographically visible division separating the corpus cerebelli and the eminentia granularis, nor the two portions of this structure. In all species examined, the lobes of the eminentia granularis are somewhat cylindrical in the dorsal view. In Siluriformes, the lateral line lobe is involved in mechano- and electrosensory stimulation and is referred to as both the medial nucleus (mechanical stimulation) and the lateral nucleus (electrical stimulation) (McCormick, 1982, 1992; Meek & Nieuwenhuys, 1998). We decided to use the general term lateral line lobe for this region, because similar terminology is used in the literature, and to avoid confusion regarding their boundaries. The lateral line lobe is located in the dorsal rhombencephalic region (Meek & Nieuwenhuys, 1998), beneath the supraoccipital process, near the suture between the pterotic and exoccipital processes (Fig. 1). It is posterolateral to the eminentia granularis and the corpus cerebelli, and lateral to the lobus facialis. Immediately below the anterior portion of this area, the rami of the nervus oculomotorius, trochlearis, trigeminus, abducens, facialis, octavus and linea lateralis anterior have projections that exit the braincase through the foramina on the pterosphenoid (Fig. 1). In almost all species examined, the lateral line lobe forms two conspicuous circular bulges with two subdivisions each (anterior and posterior). The anterior subdivision is larger than the posterior in all pseudopimelodids, except for Microglanis, which has only one circular bulge on each lateral line lobe (Figs 3–5). Usually, there is no topographically visible division separating the corpus cerebelli from the lateral line lobe, nor separating the two portions of this structure. Only C. pacifici exhibited a notch between the anterior and posterior subdivision of the lateral line lobe (Fig. 3C). The boundary of this structure differs between the species examined. In Rhyacoglanis, Batrochoglanis and Microglanis, the lateral line lobe extends to the boundary between the posterior portion of lobus facialis and the anterior portion of vagal lobe. However, in Cephalosilurus, Cruciglanis, Pseudopimelodus and Lophiosilurus, the lateral line lobe extends as far as the anterior portion of the lobus vagi (Figs 3–5). The teleostean corpus cerebelli is an unpaired protrusion on the dorsal surface of the hindbrain, a specialization located in the dorsalmost rhombencephalic region (Meek & Nieuwenhuys, 1998). This lobe is responsible for processing information from the lateral line, electrical signals, vestibular, somatosensory and auditory system signals (Finger, 1983). The corpus cerebelli is positioned immediately anterior to the lobus facialis, dorsal to the hypothalamus, and between the lobes of the tectum mesencephali (Fig. 1). In Cruciglanis, Pseudopimelodus and Rhyacoglanis, the anterior portion of this structure is positioned dorsal to the posterior area of the telencephalon. Therefore, in Batrochoglanis, Cephalosilurus, Lophiosilurus and Microglanis, the corpus cerebelli does not overlap with any portion of the telencephalon, which means that in some instances the habenula is visible (Figs 3–6). Figure 6. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in lateral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 5, lobus inferior hypothalami; 8, tectum mesencephalic; 9, corpus cerebelli; 10, lateral line lobe. Scale bars = 2 mm. Figure 6. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in lateral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 5, lobus inferior hypothalami; 8, tectum mesencephalic; 9, corpus cerebelli; 10, lateral line lobe. Scale bars = 2 mm. The corpus cerebelli had the most modifications in this study and can take several forms in the dorsal view. Geometrical shapes were used to denote the general morphologies of the corpus cerebelli. It is an ellipse in Cruciglanis and Pseudopimelodus, with the anterior and posterior portions rounded, and the posterior area slightly larger than the anterior. An oval shape is found in Rhyacoglanis, with both edges rounded, but the posterior portion is much wider than the anterior portion. Finally, in Batrochoglanis, Cephalosilurus, Lophiosilurus and Microglanis, the corpus cerebelli is triangle shaped, with the posterior portion rounded and wider than the anterior portion, which almost comes to a point (Figs 3–5). The posterior margin of the corpus cerebelli has two convex bulges in Batrochoglanis and Lophiosilurus. In Cruciglanis, Microglanis, Pseudopimelodus and Rhyacoglanis, it forms a single convex bulge, and in Cephalosilurus the posterior margin of the corpus cerebelli is straight. The anterior margin of the corpus cerebelli is rounded in all species of Pseudopimelodidae. The lateral margins of this structure are straight and anteriorly inclined. In Rhyacoglanis, the dorsal surface of the corpus cerebelli has a conspicuous longitudinal crest on the sagittal medial plane, with slight depressions on both parallel sides. In all the remaining species, this region has no noticeable undulations or ridges (Figs 3–5). In Batrochoglanis and Microglanis, the corpus cerebelli is wider than it is long. In Cruciglanis and Rhyacoglanis, the corpus cerebelli occupies the largest proportional volume of the Pseudopimelodidae brain (Table 1). In all the remaining species examined, the corpus cerebelli is only smaller than the telencephalon, but in Batrochoglanis it is also smaller than the hypothalamus (Table 1). The term ‘brainstem’ is often used in neuroanatomical papers and may refer to the ventralmost part of the brain except for any part of the diencephalon or, in fishes, include only the floor of the rhombencephalon (Nieuwenhuys & Pouwels, 1983; Butler & Hodos, 2005). We use the term truncus cerebri in an attempt to standardize the nomenclature used herein, and its boundaries are discriminated below. The truncus cerebri is located on the ventral surface of the brain and comprises the rhombencephalon and mesencephalon. More precisely, it extends from the posterior area of the chiasma opticum to the anterior area of the medulla spinalis and is located completely above the parasphenoid. Almost all cranial nerves exit from the truncus cerebri, except the nervus olfactorius and nervus opticus. The cranial nerves in this area include the oculomotor, trochlear, trigeminal, abducens, facial, octavus, glossopharyngeal, vagal, lateral line anterior and lateral line posterior (Fig. 1). No proportional length and shape modifications of the truncus cerebri were found in any of the pseudopimelodids (Fig. 7). Figure 7. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in ventral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus. Scale bars = 2 mm. Figure 7. View largeDownload slide Brain gross morphology of species of Pseudopimelodidae in ventral view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici MCP non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus. Scale bars = 2 mm. Mesencephalon The tectum mesencephali is located in the dorsal portion of the tegmentum mesencephali, covering the generally large midbrain ventricle located in the dorsalmost portion of the mesencephalon (Meek & Nieuwenhuys, 1998). Topographically, it is positioned lateral to the corpus cerebelli in the dorsal view and posterior to the telencephalon (Fig. 1). The tectum mesencephali lobes are positioned beneath the supraoccipital process and frontal. These lobes are the main recipients of retinal stimuli through the nervus opticus (visual input processing) and are also involved in the integration of visual stimuli with sensory information from other regions, resulting in the generation and coordination of motor responses (Meek & Nieuwenhuys, 1998). In Cruciglanis, Pseudopimelodus and Rhyacoglanis, the medial margin of these lobes is located under the corpus cerebelli, whereas in Batrochoglanis, Cephalosilurus and Lophiosilurus, it is located under only the anterior portion, and in Microglanis the lobes extend further beyond the anterior margin of the corpus cerebelli. The tectum mesencephali has two bilaterally rounded structures in all species examined, in the lateral and dorsal views. In these species, the tectum mesencephali completely covers the torus semicircularis. However, in Batrochoglanis, Cephalosilurus, Lophiosilurus and Microglanis, the torus semicircularis is apparent below the tectum mesencephali. The proportional volume of the tectum mesencephali is smaller than that of the hypothalamus in all Pseudopimelodidae species examined, except for Lophiosilurus, in which the opposite is true (Table 1). The nervus opticus originates in the retina and emerges topographically from the ventralmost part of the tectum mesencephali on the mesencephalon. Its efferent and afferent projections exit in the region immediately anterior to the lobus inferior hypothalami, where their fibres cross the midline of the brain around the chiasma opticum (Figs 1, 7). These fibres come into contact with each other at the base of the chiasma opticum. The projections of the nervus opticus exit the braincase through a foramen located between the frontal, orbitosphenoid and pterosphenoid. The chiasma opticum is located ventral to the preoptic area, anterior to the hypothalamus, anteromedial to the lateral preglomerular nucleus, and over the parasphenoid. In Cephalosilurus and Lophiosilurus, the nervous tractus olfactorius is thicker than the optic nerve. This relationship is inverted in Cruciglanis, Microglanis and Pseudopimelodus. In Batrochoglanis, both nerves are of approximately the same thickness. Diencephalon The teleostean hypothalamus can be subdivided into three major regions: periventricular zone, tuberal region, and inferior hypothalamic lobes (Meek & Nieuwenhuys, 1998). This region receives inputs from the rhombencephalon, mesencephalon, hypophysis and telencephalon (Kanwal, Finger & Caprio, 1988; Striedter, 1990; Wulliman & Meyer, 1990; Lamb & Caprio, 1993). The hypothalamus is located in the ventralmost part of the diencephalon, anteromedial to the hypothalamic inferior lobes. It is semicircular, with straight medial portions (Fig. 7). The pituitary gland (or hypophysis) is circular and anchored medially to the posterior portion of the hypothalamus by the pituitary stalk, which contains hypothalamic and preoptic nerve fibres involved in neuroendocrine functions (Meek & Nieuwenhuys, 1998). No proportional length and shape modifications in the pituitary gland were found in any of the Pseudopimelodidae species examined. The saccus vasculosus, a rounded, darkish structure, is located posterior to the pituitary gland. This structure is also anchored over the hypothalamus and is approximately the same size as the pituitary gland (Figs 1, 7). The lobus inferior hypothalami is located lateroposterior to the tuberal hypothalamic region. These lobes comprise the distal part of the lateral recessus, the central nucleus and the nucleus diffusus lobi lateralis. It is the largest part of the hypothalamic region in teleostean fish and receives signals from gustatory centres, the suprachiasmatic nucleus and the ventral area of the telencephalon (Kanwal et al., 1988; Striedter, 1990; Finger & Kanwal, 1992; Lamb & Caprio, 1993; Meek & Nieuwenhuys, 1998). The lobus inferior hypothalami is positioned posterior to the chiasma opticum, ventral to the truncus cerebri and tectum mesencephali, and posterior to the telencephalon. These lobes are semicircular, with the anterior portion being slightly smaller than the posterior (Fig. 1). In Pseudopimelodidae, there are some undulations and ridges on the lateral margin of these lobes. No general shape modifications were found in the lobus inferior hypothalami (Fig. 7). The lateral preglomerular nucleus is a large protrusion in the lateral surface of the brain that can also be seen in the ventral view. This lobe is involved in toral, diencephalic and telencephalic connections (Striedter, 1992). The lateral preglomerular nucleus is located anterior to the lobus inferior hypothalami, anterolateral to the hypothalamus and above the tectum mesencephali, in the lateral view. The lobes of the lateral preglomerular nucleus are rounded in all species examined (Figs 1, 6, 7). The proportional volume of the hypothalamus was determined by grouping all subdivisions of the diencephalon area. In all species examined, the proportional volume of the hypothalamus was larger than that of the tectum mesencephali, except in Lophiosilurus. In Batrochoglanis, the proportional volume of the hypothalamus is larger than that of the corpus cerebelli (Table 1). Telencephalon The telencephalon is the rostralmost subdivision of teleostean brains and comprises an area dorsalis, an area ventralis and the bulbus olfactorius (Meek & Nieuwenhuys, 1998). The area dorsalis can be subdivided further into four cytoarchitectonic areas and the area ventralis into five cytoarchitectonic areas (Meek & Nieuwenhuys, 1998), but these subdivisions were not examined. Some studies have pointed out that the dorsal area receives a series of inputs from all main regions of the brain (Finger, 1980; Kanwal et al., 1988; Resink et al., 1989; Striedter, 1991, 1992) and that the ventral area receives inputs from the bulbus olfactorius (Finger, 1975; Bass, 1981; Resink et al., 1989). The telencephalon is also involved in learning, memory, gustation and some behavioural responses (de Bruin, 1980; Finger, 1980; Savage, 1980; Kanwal et al., 1988; Lamb & Caprio, 1993; Saito & Watanabe, 2006). The telencephalon is located anterior to the tectum mesencephali, posterior to the bulbus olfactorius, and its posterior area is positioned beneath the corpus cerebelli in many species (Figs 1–6). In all species examined, the telencephalon is connected to the bulbus olfactorius by a long tract (tractus olfactorius). The telencephalon is positioned beneath the frontal and supraoccipital processes. In all species examined, the telencephalon is longitudinally elongated and somewhat cylindrical, with rounded anterior and posterior margins. Many modifications in this structure were observed from in pseudopimelodids. Although no morphological patterns were found within Pseudopimelodidae, the modifications observed here might be of interest for future studies. The posterior portion of the telencephalon is smaller than the anterior portion in B. villosus, C. apurensis, C. fowleri, P. charus and P. mangurus. In C. pacifici, M. cibelae, M. cottoides, M. garavelloi and P. bufonius, both anterior and posterior portions are the same size and maintain the same width over their length. In Batrochoglanis sp., B. raninus, B. melanurus, C. albomarginatus, L. alexandri, M. poecilus, M. secundus and Rhyacoglanis, the anterior portion is smaller than the posterior portion (Figs 3–6). In most instances, the proportional volume of this subdivision is the largest in the brain. In Cruciglanis and Rhyacoglanis, however, the proportional volume of the telencephalon is smaller than that of the corpus cerebelli (Table 1). The bulbus olfactorius receives sensory inputs from nerve cells in the olfactory epithelium via the nervus olfactorius (Meek & Nieuwenhuys, 1998). The bulbus olfactorius is located beneath the nasal bone, near the articulation between the lateral ethmoid and the vomer. This structure in all pseudopimelodids is stalked, connected to the olfactory epithelium via the nervus olfactorius and connected to the telencephalon by a long tractus olfactorius. The anterior and posterior portions of the bulbus olfactorius are rounded and fairly elliptical. No proportional length and some shape modifications in the bulbus olfactorius were found in pseudopimelodids. In general, all species examined have a rounded olfactory epithelium, with the anterior edge slightly smaller than the posterior, laterally curved with numerous lamellae on each side, like a feather (Fig. 8). Figure 8. View largeDownload slide Olfactory organ of species of Pseudopimelodidae in dorsal view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici INCIVA non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. Scale bars = 1 mm. Figure 8. View largeDownload slide Olfactory organ of species of Pseudopimelodidae in dorsal view. A, Batrochoglanis raninus MZUEL 6035, 76.73 mm standard length (SL). B, Cephalosilurus fowleri MZUEL 6040, 275.01 mm SL. C, Cruciglanis pacifici INCIVA non-catalogued, 142.45 mm SL. D, Lophiosilurus alexandri MZUEL 5377, 58.67 mm SL. E, Microglanis cottoides MZUEL 6033, 40.08 mm SL. F, Pseudopimelodus mangurus MZUEL 2795, 75.68 mm SL. G, Rhyacoglanis altiparanae MZUEL 6034, 39.18 mm SL. Scale bars = 1 mm. PHYLOGENETIC IMPLICATIONS Fink & Fink (1996) summarized a series of neural features to support the close relationship between the catfish and the electric knifefish. Details of these features are given by Albert et al. (1998) and Albert (2001). However, there is still no exhaustive knowledge of neuroanatomy for most Siluriformes, with no characters to support this clade (Wiley & Johnson, 2010). Despite the view that neural evolution involves a mosaic of functional and developmental processes (Northcutt, 1992; Striedter, 1992; Albert et al., 1998; Gonzalez-Voyer, Winberg & Kolm, 2009), patterns might be incorporated in evolutionary interpretations (Eastman & Lannoo, 1998; Albert, 2001; Di Dario & de Pinna, 2006; de Pinna, Ferraris & Vari, 2007; Rosa et al., 2014; Abrahão & Shibatta, 2015). Studies on fish nervous systems are still needed to elucidate fully the evolutionary processes involved. Brain gross morphology varies greatly in Pseudopimelodidae. There are considerable differences in the shape and size of the main subdivisions. Furthermore, a few intraspecific modifications were observed in some subdivisions. These intraspecific modifications are more conspicuous in the telencephalon, with the anterior portion sometimes being more bulged and larger than the posterior portion, but also sometimes not bulged and smaller. However, these features were not considered informative characters because of the considerable variation in lobe format in the specimens examined. The combination of considerable interspecific modification and restricted intraspecific variation suggests that brain gross morphology provides putative characters for the resolution of supraspecific groups. In addition, the morphological patterns shared by species within these groups are indicative of the fact that these characters might be useful in phylogenetic analyses. Notwithstanding their putative conservativeness, optimization of the proposed characters can highlight differences, if analysed with respect to existing hypotheses. Pimelodoidea The brain gross morphology of Pseudopimelodidae species examined is similar to closely related families in the superfamily Pimelodoidea, a clade well corroborated on the basis of molecular (Hardman, 2005; Sullivan et al., 2006, 2013) and morphological (Lundberg et al., 1991; Bockmann, 1998; Bockmann & Guazzelli, 2003; Britto, 2003; Lundberg & Littmann, 2003; Shibatta, 2003; Birindelli & Shibatta, 2011) characters, as follows: the lobus vagi composed of two cylindrical, paired, V-shaped lobes; lateral line lobe consisting of two conspicuous bulges, oval in shape, with the anterior portion more prominent than the posterior portion; and olfactory epithelium with numerous lamellae. As evidenced in the Heptapteridae species examined, the pituitary gland is displaced towards the medial region of the hypothalamus; the anterior portion of the lobus vagi is bulged; the intumescence on the lobus facialis is displaced towards the lateral portion; the lateral line lobe has two conspicuous bulges with no notch between them; the dorsal surface of the corpus cerebelli has no conspicuous crest; the corpus cerebelli is trapezoidal, extending upward less than half length of the telencephalon; and the corpus cerebelli is longer than the telencephalon. In the Pimelodidae species examined, the pituitary gland is displaced towards the posterior region of the hypothalamus; the anterior portion of the lobus vagi is bulged; the intumescence on the lobus facialis is displaced towards the anterolateral portion; the lateral line lobe has two conspicuous bulges with no notch between them; the dorsal surface of the corpus cerebelli has no conspicuous crest; the corpus cerebelli is rectangular, extending up to more than half length of the telencephalon; and the corpus cerebelli is greater in length than the telencephalon. Until recently, Pseudopimelodidae was recognized as belonging to the family Pimelodidae. The monophyly of the three subfamilies that made up Pimelodidae (Pimelodinae, Pseudopimelodinae and Heptapterinae) was proposed by Lundberg & McDade (1986) and Lundberg et al. (1988, 1991). This hypothesis gave rise to discussions regarding the phylogenetic position of the family. Pseudopimelodinae was considered a sister group of Heptapterinae (= Heptapteridae), based on the lip structure (Lundberg et al., 1988, 1991). Later, in a comprehensive phylogenetic analysis of Siluriformes, de Pinna (1993, 1998) considered Pseudopimelodinae as related to a clade consisting of Sisoroidea, Amphiliidae and Loricarioidea; Heptapterinae was included in a subgroup of Bagridae, and Pimelodinae was placed in a distal position as another subgroup of Bagridae. The close relationships between Pseudopimelodidae, Pimelodidae and Heptapteridae, placing them in a clade that also included Doradoidei and other groups, was recovered by Britto (2003). The families Pseudopimelodidae and Heptapteridae occupied the basal position in this clade. Using myology data, Diogo (2004) and Diogo et al. (2004) proposed that Pseudopimelodidae was a sister group to a clade formed by Pimelodidae and Heptapteridae. The molecular data recovered Pseudopimelodidae as a sister group of Pimelodidae, and the clade as a sister group of Heptapteridae plus Conorhynchos (Hardman, 2005; Sullivan et al., 2006). Most recently, a molecular-based study using nuclear and mitochondrial sequences provided strong support for the monophyly of the Pimelodoidea clade (Sullivan et al., 2013) formed by {[Conorhynchos plus Heptapteridae] [Pimelodidae (Pseudopimelodidae plus Phreatobius)]}. The similar structure of the constrictor muscle of the gas bladder in Pimelodidae and Pseudopimelodidae (Birindelli & Shibatta, 2011) was used as evidence for the sister group relationship between Pimelodidae and Pseudopimelodidae. The molecular studies of Sullivan et al. (2013) arrived at the same relationship scheme. Shibatta & Vari (2017), using morphological data, disagreed with that hypothesis. Data from neuroanatomical features was congruent with the first two hypotheses (Fig. 9). Based on the material examined herein, pseudopimelodids and pimelodids share three features of the encephalon, with Heptapteridae as sister to them. The first [1] is the position of the intumescence on the lobus facialis, which is oriented along the entire lateral margin on each lobe, in examined Heptapteridae species. Each lobe appears to have two regions longitudinally subdivided into two equal halves. In most Pseudopimelodidae and Pimelodidae species, this intumescence is located along the anterolateral portion. It occupies half the width of each lobe in the posterior portion and extends to the anteromedial portion (Figs 3–5, 10). A second possible synapomorphy for Pimelodidae plus Pseudopimelodidae is [2] the prolongation of the posterior portion of the lateral line lobe. In Heptapteridae, this region ends abruptly and reaches only half the length of the lateral margin of the lobus facialis. This condition is not found in Pimelodidae and most Pseudopimelodidae species (Figs 3–5, 10). In the material examined from these families, this posterior portion has a tail-shaped prolongation that extends up to the division between the lobus facialis and lobus vagi. The last possible synapomorphy for these two families is [3] the size of the saccus vasculosus. This structure can appear and disappear among teleosts. In Siluriformes, this diencephalic structure is characterized as well developed and moderately developed in most families. In Heptapteridae, the saccus vasculosus is smaller than the pituitary gland. However, in all the species of Pimelodidae and Pseudopimelodidae examined, this relationship is inverted, and the saccus vasculosus is the same length or longer than its anterior structure, the pituitary gland (Figs 7, 10). The independent and congruent signals provided by molecular and morphological data from the gas bladder and encephalon indicate that Heptapteridae is possibly the sister group of a clade with Pimelodidae and Pseudopimelodidae. Figure 9. View largeDownload slide Maximum parsimony optimization of the identified derived characters of the gross morphology of the brain superimposed on the cladogram of Pseudopimelodidae proposed by Shibatta & Vari (2017). Characters are numbered as described in the main text. Characters in green are putative synapomorphies for groups. Characters in red are homoplastic optimizations. Figure 9. View largeDownload slide Maximum parsimony optimization of the identified derived characters of the gross morphology of the brain superimposed on the cladogram of Pseudopimelodidae proposed by Shibatta & Vari (2017). Characters are numbered as described in the main text. Characters in green are putative synapomorphies for groups. Characters in red are homoplastic optimizations. Figure 10. View largeDownload slide Brain gross morphology of species of the outgroup in dorsal, lateral and ventral views, from left to right. A, Steindachneridion parahybae MZUEL 5231, 262.41 mm standard length (SL). B, Goeldiella eques MZUEL 7417, 57.1 mm SL. C, Diplomystes mesembrinus MZUSP 62595, 97.5 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Figure 10. View largeDownload slide Brain gross morphology of species of the outgroup in dorsal, lateral and ventral views, from left to right. A, Steindachneridion parahybae MZUEL 5231, 262.41 mm standard length (SL). B, Goeldiella eques MZUEL 7417, 57.1 mm SL. C, Diplomystes mesembrinus MZUSP 62595, 97.5 mm SL. 1, telencephalon; 3, lateral preglomerular nucleus; 4, hypothalamus; 5, lobus inferior hypothalami; 6, hypophysis; 7, saccus vasculosus; 8, tectum mesencephali; 9, corpus cerebelli; 10, lateral line lobe; 11, lobus facialis; 12, lobus vagi; 13, medulla oblongata. Scale bars = 2 mm. Pseudopimelodidae The monophyly of Pseudopimelodidae has been supported to date with morphological data by Lundberg et al. (1991), Shibatta (1998) and Shibatta & Vari (2017), and by Sullivan et al. (2013) with molecular data. In all species examined here, each lobe of the lobus vagi comes into contact posteriorally, forming an acute tip in the dorsal view. At least one derived condition of the lobus vagi in Pseudopimelodidae can be a putative synapomorphy for the family: [4] the absence of a conspicuous bulge on the anterior portion of this lobe (Figs 3–5, 9, 10). This lobe has anterior and posterior portions of the same width, in the dorsal view. Similar arrangements are observed only in some phylogenetically non-related groups (Pupo, 2015). In the examined species of Heptapteridae and Pimelodidae, this region has a conspicuous bulge on the anterior portion of the lobus vagi (Figs 3–5, 10). The previous analyses by Ortega-Lara & Lehmann (2006) presented the hypothesis that Pseudopimelodidae is composed of two major clades: the first with Pseudopimelodus, Cruciglanis, Batrochoglanis and Microglanis; and the second with Cephalosilurus and Lophiosilurus. This relationship scheme disagrees with the conclusions of Shibatta & Vari (2017). In this later study, Pseudopimelodidae is also composed of two major clades, but with some important differences: the first grouping is Pseudopimelodus, Cruciglanis and Rhyacoglanis; and the second is Cephalosilurus, Lophiosilurus, Batrochoglanis and Microglanis. Data from the brain are more congruent with this later hypothesis (Fig. 9). Based on the material examined, Cephalosilurus, Lophiosilurus, Batrochoglanis and Microglanis share two notable derived features. The first [5] is the general shape of the corpus cerebelli, somewhat triangular, with the posterior margin straight and much larger than the anterior margin, which can be rounded or at an acute angle (Figs 4, 5). The second [6] is the prolongation of the anterior portion of the corpus cerebelli, which extends as far as the boundary between the mesencephalon and the telencephalon but does not come into contact with the latter, exhibiting the habenula in the dorsal portion of the diencephalon (Figs 4, 5). In turn, Pseudopimelodus, Cruciglanis and Rhyacoglanis share one derived feature: the prolongation of the anterior portion of the corpus cerebelli [6] extends beyond the mesencephalon, but by less than half the length of the telencephalon (Fig. 3). Cephalosilurus and Lophiosilurus species share two features: an anterior intumescence on the lobus facialis [1] and the smaller size of this lobe [7] (Fig. 9). The intumescence is located only in the anterior portion on the lobes of the lobus facialis. In this conformation, the intumescence extends over the entire width of the anterior portion, dividing each lobe horizontally by two-thirds (Fig. 4). The extension of the lobus facialis comprises a half medial margin of the lateral line lobe. This feature is easily visible, projecting before the posterior portion of the lateral line lobe (Fig. 4). This close relationship is corroborated in all existing hypotheses (Ortega-Lara & Lehmann, 2006; Shibatta & Vari, 2017). In addition, species of Batrochoglanis and Microglanis also share two possible synapomorphies: the general format of the corpus cerebelli [8]; and the shorter length of the corpus cerebelli compared with the telencephalon [9] (Fig. 9). The corpus cerebelli is usually elongated sagitally in most Siluriformes. In most species examined, the corpus cerebelli is longer than its posterior width. However, in Batrochoglanis and Microglanis, this relationship is inverted. The corpus cerebelli is the most elongated subdivision of the brain in most species of Siluriformes. However, in the species of Batrochoglanis and Microglanis, the corpus cerebelli is decreased. In these genera, the telencephalon is longer than the corpus cerebelli and all other brain subdivisions (Fig. 5). These two genera were also closely related in the phylogenetic analysis proposed by Ortega-Lara & Lehmann (2006) and Shibatta & Vari (2017). The proposal formulated by Ortega-Lara & Lehmann (2006), that Pseudopimelodus is the sister group of a clade composed of Cruciglanis plus Batrochoglanis and Microglanis, disagrees with the hypothesis proposed by Shibatta & Vari (2017). In the latter, Pseudopimelodus is sister to Cruciglanis, and this clade is sister to Rhyacoglanis. Data from the brain are more congruent with this hypothesis (Fig. 9). Based on the material examined, Pseudopimelodus and Cruciglanis share two putative synapomorphies: the prolongation of the posterior portion of the lateral line lobe [2]; and the general shape of the corpus cerebelli [5]. The posterior portion of the lateral line in these species is extended until the anterior portion of the lobus vagi (Fig. 3). This derived condition is not found in other any species examined. In Pseudopimelodus and Cruciglanis, the anterior and posterior margins of the corpus cerebelli are equally rounded and somewhat elliptical (Fig. 3). Brain gross morphology data are consistent with the hypothesis of Shibatta (1998) and Shibatta & Vari (2017) of a monophyletic clade formed by Rhyacoglanis (Fig. 9). The corpus cerebelli in all these species is the same shape and has a conspicuous crest on the dorsal surface [10]. This crest is formed by depressions in the parasagittal plane. In these species, the crest is sagittally positioned along almost the entire length of the dorsal surface of the corpus cerebelli (Figs 3–5, 10). The remaining species examined herein do not have this crest. Therefore, this exclusive feature can be a possible synapomorphy for this genus. This group also has the coloration and body morphological features that differentiate it from the remaining pseudopimelodids (Shibatta, 1998; Shibatta & Vari, 2017). Likewise, the brain characters of Microglanis are consistent with the hypothesis of monophyly, with the lateral line lobe consisting of only one bulge, without any clear separation in the middle [11]. This derived condition is found only in other families of Siluriformes. Diplomystidae and other related groups have this condition, therefore, are possible synapomorphies for this genus (Fig. 5). In the remaining species of Pseudopimelodidae, the lateral line lobe has a clear separation located approximately in the middle of the structure. Where this separation into two bulges is found, the anterior bulge always protrudes further than the posterior one (Figs 3–5, 10). In addition, the volume of the corpus cerebelli compared with the volume of the hypothalamus is a character that supports the monophyly of Batrochoglanis. In these species, the hypothalamus is more robust and occupies a wide area in the ventral region of the brain (Table 1). The other species of Heptapteridae and Ictaluridae examined as comparative material have the same relationship between these two subdivisions [12]. Lastly, C. pacifici has a conspicuous notch between the anterior and posterior bulges of the lateral line lobe [13], a further autapomorphy for this monotypic genus. The monophyly of these last three genera was determined by Ortega-Lara & Lehmann (2006) and Shibatta & Vari (2017) (Fig. 9). ECOLOGICAL AND BEHAVIOURAL NOTES A comparison among all examined species of Pseudopimelodidae presented differences in the volume of the major subdivisions of the brain, which may be associated with their behavioural and ecological characteristics. These associations have been empirically tested by many authors and have proved to be realistic, principally when focusing on closely related groups (Evans, 1940; Ridet & Bauchot, 1990; Eastman & Lannoo, 1995; van Staaden et al., 1995; Kotrschal et al., 1998). Furthermore, the modifications in the size of brain subdivisions are reliable predictors of their relative importance (Kishida, 1979; Kotrschal & Palzenberger, 1992; Kotrschal et al., 1998). Within Otophysi (sensuWiley & Johnson, 2010) and in relationship to the other groups, Characiformes and Gymnotiformes (e.g. Albert, 2001; Pereira & Castro, 2016), Cypriniformes and Siluriformes have well-developed gustative lobes, with elaborate external taste and tactile systems (Marui, 1977; Marui & Caprio, 1982; Marui et al., 1988; Angulo & Langeani, 2017). The species of Pseudopimelodidae follow the same pattern; the lobus vagi and the lobus facialis are developed and occupy a broad area in the dorsal region of the rhombencephalon. The majority of Pseudopimelodidae species can be categorized as omnivorous or carnivorous, feeding on allochthonous insects, algae, vegetal debris and fishes (Shibatta, 1998). In accordance with Shibatta’s observations, there are no great variations in volume of the gustative lobe region in all specimens examined (Table 1), evidencing similar feeding behaviour. Although the corpus cerebelli is the largest subdivision in various groups of Otophysi (Brandstätter & Kotrschal, 1990; Albert, 2001; Ching, Senoo & Kawamura, 2015; Pereira & Castro, 2016; Angulo & Langeani, 2017), in Pseudopimelodidae the sizing varies between genera. At one end of this spectrum are species of Pseudopimelodus, with the largest and most voluminous corpus cerebelli (Table 1). Larger corpus cerebelli may be linked to increased motor control while swimming in structurally complex environments (Bauchot et al., 1989; Kotrschal et al., 1998). This theory is in accordance with observations on the habitat and distribution of these species. These species inhabit the main channels of rivers, with strong rapids and rocky bottoms (Shibatta, 1998). At the other extreme, species of Microglanis and Batrochoglanis have the smallest and least voluminous corpus cerebelli (Table 1). These results may also be related to their habitat and distribution, because they are commonly found in riparian vegetation, hidden among the roots of macrophytes, with weaker rapids (Oscar A. Shibatta, personal observation). The dorsal region of the mesencephalon is more voluminous in Lophiosilurus (Table 1). According to Shibatta (1998), this species is not active and is an ambush predator, buried in the sand. The increase of this subdivision may be related to visual acuity, despite other functions related to this region (i.e. Huber et al., 1997; Wagner, 2003). All remaining species are active predators, swimming among rocks, trunks and roots to hunt their prey. Our results suggest that the size of brain subdivisions in species of Pseudopimelodidae varies with feeding behaviour and preferred environment. However, these associations are based only on empirical data from a series of other studies with other groups of fishes, as cited above. Therefore, despite the logic of these associations, empirical analyses are needed. Although comparative neurobiologists have made advances in establishing when and in what ways brain morphology has changed, there has been little progress in understanding how and why such changes have occurred. This is, in part, attributable to a lack of studies focused on comparative neuroanatomy. Research on ontogenetic transformations should be used to understand changes over time and to provide robust information on the mechanisms for change. Finally, an interdisciplinary approach that includes anatomy, physiology, ethology, ontogeny and phylogeny is required to understand these mechanisms (Northcutt, 2002). This study is the first step towards comprehending what changes occurred in Pseudopimelodidae brains, with some speculation on when these modifications occurred, based on recent phylogenetic hypotheses. New research on Siluriformes should test these assumptions in brain evolution. ACKNOWLEDGEMENTS The authors are grateful to Luiz Peixoto and Gustavo Ballen (MZUSP) for reading and commenting on the manuscript. We thank Mario de Pinna (MZUSP), Ricardo Castro (LIRP), Lucia Py Daniel (INPA), Luiz Malabarba (MCP), Pablo Lehmann (MCP), Francisco Provenzano (MBUCV), Mary Burridge (ROM) and Germán Parra (INCIVA-IMCN) for the loan of specimens and permission to dissect them. This project had the logistical support of Edson Santana (UEL) in collections and laboratorial issues, and Silvia Ponzoni (UEL) for assistance in the physiological laboratory. The authors are extremely grateful to two anonymous reviewers and to Louise Allcock, the editor of this journal. The careful and constructive comments certainly benefited the paper. O.A.S. is a research fellow of the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico/process 304868/2015-9). 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Zoological Journal of the Linnean SocietyOxford University Press

Published: Apr 3, 2018

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