TY - JOUR
AU - Griffiths, Charles, L
AB - Abstract The herbivorous amphipod Sunamphitoe robertan. sp. is described from the canopy of kelp beds in False Bay, South Africa. The new species has unusual habits, small family groups burrowing directly into the margins of the swollen primary fronds of the kelp Ecklonia maxima (Osbeck) Papenfuss, 1940. Morphologically, the new species is best distinguished from other species of Sunamphitoe by strong rows of dorsal spines on the outer rami of uropods 1 and 2. These spine rows appear to be employed as ‘drill-bits’ to excavate kelp tissue and create the burrows. Damage to hosts does not appear to be fatal, but requires further investigation. INTRODUCTION Members of the amphipod genus SunamphitoeSpence Bate, 1857 are large, robust, herbivorous amphipods, usually associated with large brown algae, especially kelps. Most species use their glandular pereopods to produce a silk that is used to stitch or glue the algal fronds together, forming chambers within which they shelter while feeding (Griffiths, 1979; Cerda et al., 2009). These species generally cause relatively little damage to their host algae (Poore & Steinberg, 2001; Cerda et al., 2009), although one species, S. stypotrupetes (Conlan & Chess, 1992), bores into the stipes of kelps and then feeds on the inner stipe tissue, killing large numbers of hosts at some sites (Chess, 1993). Sunamphitoe now incorporates all species previously included within the genus PeramphithoeConlan & Bousfield, 1982. The two genera were previously distinguished solely by the condition of the mandibular palp, this being absent in Sunamphitoe, but present in Peramphithoe. Recent morphological and molecular analyses (Peart & Ahyong, 2016; Sotka et al., 2017), however, have shown that species from the two genera are genetically interspersed, suggesting the mandibular palp has been lost multiple times during the evolution of the group and is hence not a generically significant feature. The amalgamated genus Sunamphitoe thus currently comprises 29 species, the phylogentic relationships of which have been examined in detail by Peart (2017). Only two species of Sunamphitoe had been reported from South Africa prior to the present study. The first of these, S. falsa (K.H. Barnard, 1932), was originally described as Ampithoe falsa and transferred to the genus Peramphithoe by Conlan & Bousefield (1982). The species was also described (as A. falsa) from the Red Sea (Ruffo, 1969). The second species, S. africanaMilne & Griffiths, 2013 was originally reported as Ampithoe humeralis by Griffiths (1979), and later transferred to Peramphithoe by Conlan & Bousfield (1982). Based on differences those authors identified between the South African specimens and the true North American S. humeralis, Milne & Griffiths (2013) gave the South African form separate species status. While surveying the canopy fauna of kelp beds in False Bay, South Africa, the author collected a species of Sunamphitoe burrowing into the swollen ‘heads’ or primary fronds of the kelp Ecklonia maxima (Osbeck) Papenfuss, 1940. This did not correspond to any known species within the genus and is described here as new. SYSTMATICS Genus SunamphitoeSpence Bate, 1857 SunamphitoeSpence Bate, 1857: 147; J.L. Barnard & Karaman, 1991: 111; Peart, 2017: 303. PeramphithoeConlan & Bousfield, 1982: 60; J.L. Barnard & Karaman, 1991:111. Sunamphitoe roberta n. sp. (Figs. 1–3) Figure 1. View largeDownload slide Sunamphitoe robertan. sp. Holotype male, MB-A067535, 16 mm. Lateral view (A). antenna 1 (B), gnathopod 1 (C) with palm enlarged 3×; gnathopod 2 with palm enlarged 3× (D), pereopod 4 (E), pereopod 5 (F), pereopod 6 (G). pereopod 7 (H). Figure 1. View largeDownload slide Sunamphitoe robertan. sp. Holotype male, MB-A067535, 16 mm. Lateral view (A). antenna 1 (B), gnathopod 1 (C) with palm enlarged 3×; gnathopod 2 with palm enlarged 3× (D), pereopod 4 (E), pereopod 5 (F), pereopod 6 (G). pereopod 7 (H). Figure 2. View largeDownload slide Sunamphitoe robertan. sp. Holotype male, MB-A067535, 16 mm. Upper lip (A), mandible (B), lower lip (C), maxilla 1 (D), maxilla 2 (E), maxilliped (F), uropod 1 (G), uropod 2 (H), uropod 3 (I), telson (J). Figure 2. View largeDownload slide Sunamphitoe robertan. sp. Holotype male, MB-A067535, 16 mm. Upper lip (A), mandible (B), lower lip (C), maxilla 1 (D), maxilla 2 (E), maxilliped (F), uropod 1 (G), uropod 2 (H), uropod 3 (I), telson (J). Figure 3. View largeDownload slide Author holding swollen ‘head’ or primary frond of Ecklonia maxima, the pale upper margin of which has been burrowed into by Sunamphitoe robertan. sp. (A); freshly sectioned primary blade showing S. robertan. sp.in situ in their burrows. Note newly-emerged juveniles bottom centre (B). Photos by Craig Foster. Figure 3. View largeDownload slide Author holding swollen ‘head’ or primary frond of Ecklonia maxima, the pale upper margin of which has been burrowed into by Sunamphitoe robertan. sp. (A); freshly sectioned primary blade showing S. robertan. sp.in situ in their burrows. Note newly-emerged juveniles bottom centre (B). Photos by Craig Foster. Holotype: MB-A067535; dissected male, 16 mm, extracted from primary blade of Ecklonia maxima at water surface (growing at 5 m depth), off Miller’s Point, False Bay (34o13′42.45′′S, 18o28′19.05′′E), collected by Charles Griffiths and Craig Foster, 22 December 2017. Paratypes: MB-A067536; 6 loose adults 10–15 mm length, 1 juvenile 5 mm length, plus 3 adults (not measured) still inside tunnels excavated in a piece of primary frond of E. maxima, from same sample as holotype. Other material: MB-A067537; 5 adults 8–12 mm body length, 1 juvenile 4 mm length extracted from head of a beach-cast E. maxima, Miller’s Point, False Bay (34o 13′59.64′′S, 18o 28′30.74′′E), collected by Craig Foster, 8 January 2018. Description (holotype male 16 mm): Body robust, stout, lacking any dorsal spines or projections; almost cylindrical in cross section, with hard, brittle exoskeleton. Head as long as 1.5 pereon segments, as deep as long, notched above eye to accommodate base of antenna 1. Eye white with red centre when alive, rapidly becoming colourless in alcohol. Coxae 1–4 elongate-oval, smoothly rounded distally, with few setae on ventral margin, somewhat deeper than corresponding pereon segments, coxa 5 deeply bilobed to accommodate base of expanded pereopod 5; coxae 6, 7 much shorter, oval to rectangular. Pleon segments robust, lacking dorsal ornamentation, pleonal epimera broadly rounded, without posterodistal teeth, serrations or notches. Antenna 1 about 40% body length, peduncle about half length of flagellum, article 2 as long as article 1 but more slender, article 3 about 30% length of article 1; accessory flagellum absent, flagellum of 30 articles. Antenna 2 more robust than antenna 1 and about 60% of its length, curved ventrally, flagellum of 10 segments. Upper lip rounded, slightly notched terminally, apex covered in fine mat of tiny setae. Mandible conspicuously large, powerful, incisor with 7 strongly-chitinised (brown) teeth, lacinia mobilis with oblique row of about 8–10 fine teeth; spine row of about 10 shortish spines, molar elevated, rounded; palp 3-articulate, article 3 with about 11 strong terminal setae. Lower lip with distinct, rounded inner lobes, outer lobes notched with narrow, projecting outer shoulders. Maxilla 1 large, robust, inner plate small, rounded, outer plate with 2 very strong thick terminal teeth distally, 8 additional serrate spines medially; palp 2-articulate, extending well beyond outer plate, ending in about 6 short spines. Maxilla 2, outer plate with about 50 dense setae, inner plate with about 20 medial and distal setae. Maxilliped with inner plate medially setose, large outer plate armed with about 26 strong medial spines, these becoming longer and more slender distally, palp strong. Gnathopods both subchelate, gnathopod 1 somewhat smaller, more slender that gnathopod 2. Gnathopod 1 with article 2 not distally lobed, article 5 not distinctly lobed posteriorly, article 6 similar in length and width of article 5, palm transverse, slightly extended towards defining angle, which is acute, not toothed, dactly slightly exceeding palm by about 10%. Gnathopod 2 slightly heavier, article 2 not lobed, article 5 somewhat lobed posteriorly, distinctly shorter than article 6, article 6 not widening distally, parallel-sided, palm transverse, slightly sinuous, much shorter than hind margin, dactyl with rounded teeth on inner margin, exceeding palm by about 30%. Pereopods 3, 4 very similar, article 2 expanded, distinctly notched about halfway along posterior margin; article 4 lobed anteriorly, extended distally to partially overlap article 5. Pereopod 5 conspicuously short, powerful, article 2 conspicuously broad, rounded, almost circular, articles 4–6 broad, thickened, article 6 with 3 strong posterior spines and powerful, strongly-curved prehensile dactyl. Pereopod 6, 7 successively longer (1.5× and 1.7× length of 5 respectively), more slender, but still with articles 4, 5 noticeably thickened, article 6 with strong anterior spines. Pleopods unusually long, robust, extending some 70% of length of pereopod 7. Uropods 1 large, robust, peduncle broad, with strong triangular ventral tooth projecting about 25% length of rami, rami about half length of peduncle; outer ramus broad, dorsally rounded, with very conspicuous row of 12 strong dorsal spines, these increasing in both length, strength distally; inner ramus similar in length, tapering distally, dorsally smooth, ending in single strong, terminal spine. Uropod 2 similar in shape, structure to uropod 1, but about 75% of its length, peduncle with small terminal tooth ventrally; outer ramus with 9 conspicuously strong dorsal spines, inner ramus similar in length, tapering, smooth dorsally, with single strong terminal tooth. Uropod 3 of typical ampithoid form, with short unarmoured peduncle, rami slightly shorter than peduncle; outer ramus with 2 conspicuously strong hooked spines dorsally near apex; inner ramus slightly shorter than outer, laterally flattened, rectangular, with squared-off end bearing about 6 setae plus very short spine. Telson entire, very thick, fleshy, slightly produced distally, with 2 small spines plus short seta at each terminal corner. Variation: Very little sexual dimorphism apparent, females resembling males except for presence of marsupial plates. None of the females observed were ovigerous. Juveniles initially have fewer of the distinctive, large dorsal spines in rami of uropods 1 and 2. Etymology: The name is used as a noun in apposition and the species is named after the author’s wife, Dr Roberta Griffiths, who has waited many years, and long after both our children, to have a species named after her! The right species has finally come along though, as both amphipods and kelp beds played important roles in our working lives together as marine biologists. Nomenclatural statement: A life science identifier (LSID) number was obtained for the new species: urn:lsid:zoobank.org:pub: urn:lsid:zoobank.org:pub:4E7AC879-6A62-4744-93E7-36870 C412C41. DISCUSSION As currently constituted, Sunamphitoe comprises 29 species and the phylogenetic relationships between these have recently been the subject of a detailed review by Peart (2017). She also described eight new species within the genus, as well as listing the morphological characters that can be used to differentiate all know species. Many of the species in the genus, including the South African S. falsa, have an enlarged male gnathopod 2 with oblique, poorly defined palm, which is quite unlike the condition here, where the gnathopod 2 of males is not enlarged and has a short, transverse palm. All species in the original genus Sunamphitoe, before its amalgamation with Peramphithoe, also lack a mandibular palp, as this was the only factor distinguishing these genera prior to their amalgamation. Sunamphitoe robertan. sp. appears to fall into the clade identified by Peart (2017) as Clade 32, which is characterised by having a combination of no terminal lobe on article 2 of gnathopod 1, unexpanded article 6 of gnathopod 2, and reduced setation on rami of uropods. The other species in this group are S. aorangi (J.L. Barnard, 1972) from New Zealand, S. spuria (Krapp-Schickel, 1978) from the Mediterranean, S. humeralis (Stimpson, 1864) from Pacific North America, and the South African species, S. africanaMilne & Griffiths, 2013. Sunamphitoe robertan. sp. can, however, be easily distinguished from all these species (and indeed from all other members of the genus), but its extremely strongly-armoured and distinctive uropods 1 and 2, which bear rasp-like combs of large, robust spines along their dorsal margins. A key distinguishing the three South African species is provided below: Key to South African species of Sunamphitoe: Gnathopod 2 much larger than 1, article 6 much longer and broader than 5, with oblique, poorly defined palm S. falsa Gnathopod 2 only slightly larger than 1, articles 5 and 6 comparable in size, 6 with transverse, well defined palm 2 Outer rami of uropods 1 and 2 sparsely spinose dorsally; nests woven from folded secondary fronds of kelp Ecklonia maximaS. africana Outer rami of uropods 1 and 2 armed with rows of strong spines dorsally; burrows into primary fronds of kelp, Ecklonia maxima S. robertan. sp. The new species also bears some resemblance to the sympatric Macropisthopus stebbingi K.H. Barnard, 1916, which shares many characters (mandible with palp, no lobe on gnathopod 1, unmodified and weak gnathopod 2, poor setation on uropods), but has been maintained in a separate monospecific genus, based on its greatly expanded pereopod 7. Griffiths (1979) has argued that this character was insufficient to warrant a generic distinction, but this suggestion has not been adopted by later authors, including Milne & Griffiths (2013) and Peart (2017), who continued to retain the monospecific genus Macropisthopus. Inclusion of this species into the morphological and molecular phylogenetic analyses, as carried out by Peart (2017), could finally resolve the long-standing uncertainty regarding the true generic position of this species and it seems likely that it should be included within Sunamphitoe and is related to S. robertan. sp., which also has expanded pereopods, although not nearly as large as those of M. stebbingi. The new species has to date only been recorded burrowing onto the primary blades of large adult sporophytes of the kelp Ecklonia maxima in False Bay, South Africa. In the mature stage of this kelp, known locally as ‘sea bamboo,’ the primary blade is expanded into a broadly-triangular or rhomboid, gas-filled bulb, from which the secondary blades extend laterally (Stegenga et al., 1997). The secondary blades of older specimens often break free, leaving the primary blade as a bare, spade-like bulb and exposing the softer internal tissue of the primary blade along its lateral and distal margins (Fig. 3A). The amphipods appear to burrow into this eroded edge. The burrows take the form of short caverns or U-shaped tunnels, which each host from one to several amphipods (Fig. 3B). The burrows are thought to be created using the unusually strongly armoured and spined uropods 1 and 2, which appear to act as ‘drill-bits’ to excavate the tunnels. These spines were often clogged with kelp debris in freshly collected specimens, supporting their role as excavation tools. Direct damage to the kelps appears to be minimal, as the tunnels were never observed to penetrate into the gas-filled bulb, which thus continues to buoy up the kelp. Damage caused by this species thus appears to be far less than that caused by the stipe-boring Sunamphitoe styotreupesConlan & Chess, 1992, which severely damages and hollows-out stipes of the kelp Laminaria setchellii P.C. Silva, 1957, ultimately killing the kelp and, under suitable conditions, destroying entire beds of algae (Chess, 1993). It is, however, possible that secondary blade formation or growth is compromised by the damage to the primary blade. For example, Poore et al. (2018) found that nest-building by the related ampithoid Pseudopleonexes lessoniae (Hurley 1945) on blades of the kelp Macrocystis pyrifera (Linnaeus) C. Agardh, 1820 resulted in considerable reductions in the length and surface area of infected blades. Neither the proportions, nor size ranges of kelps infected, nor the numbers and population structure of groups inhabiting individual burrows, were investigated during this study, which aimed simply to describe the species. Both these parameters are obvious topics for a later ecological study, which should also examine the distribution of the species, which is likely to extend well beyond False Bay, since the host kelp, E. maxima, has an extensive regional range from Cape Agulhas in the east to north of Luderitz, Namibia (Stegenga et al., 1997). ACKNOWLEDGEMENTS My sincere thanks to Craig and Tom Foster for assistance with the collection of samples and to Colleen Lindberg, who first noticed this species while working on the fauna of kelp canopies and brought it to my attention. Financial support was provided though a National Research Foundation Incentive Grant (96043) to the author. Specimens were collected under research permit number RES2018/53, issued jointly by the South African Departments of Environmental Affairs and of Agriculture, Forestry and Fisheries. Rachael Peart kindly provided additional literature and commented on a draft of the manuscript. 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Descriptions of new species of marine invertebra from Puget Sound, collected by the naturalists of the North-west Boundary Commission, A. H. Campbell, Esq., Commissioner . Proceedings of the Academy of Natural Sciences of Philadelphia , 16 : 153 – 165 . WorldCat © The Author(s) 2019. Published by Oxford University Press on behalf of The Crustacean Society. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)
TI - A new species of Sunamphitoe (Amphipoda: Ampithoidae) that bores into the primary fronds of kelps in South Africa
JF - The Journal of Crustacean Biology
DO - 10.1093/jcbiol/ruz016
DA - 2019-07-24
UR - https://www.deepdyve.com/lp/oxford-university-press/a-new-species-of-sunamphitoe-amphipoda-ampithoidae-that-bores-into-the-CjWPytFauO
SP - 436
VL - 39
IS - 4
DP - DeepDyve
ER -