Journal of Morphology

doi: 10.1002/jmor.21730pmid: N/A

Plandin, Feodor A.; Temereva, Elena N.

doi: 10.1002/jmor.70082pmid: 40862630

Craniiformea is a clade of brachiopods, insufficiently studied in terms of functional morphology. While the valve‐opening mechanism in Linguliformea and Rhynchonelliformea has been reconstructed, the data on the same mechanism in Craniiformea are incomplete, although several hypotheses concerning this issue have been provided since the end of the 19th century. To review these hypotheses, we have studied the ultrastructure of the main visceral coelomic compartments and the muscles involved in shell movements in Novocrania anomala. Our data document that the lateral oblique muscles, together with a well‐developed longitudinal musculature of the body wall (described in craniiforms for the first time) compress the perivisceral coelom along the antero‐posterior axis. As a result, the perivisceral coelom expands dorso‐ventrally, pushing the dorsal valve up. Thus, that the valve‐opening mechanism in Craniiformea is, in principle, similar to that in Linguliformea. We also describe the smooth and cross‐striated parts of the anterior adductors, and demonstrate that all muscles of N. anomala are formed by myoepithelial cells.

Zaitseva, Olga V.; Smirnov, Roman V.; Petrov, Sergey A.; Petrov, Anatoly A.

doi: 10.1002/jmor.70079pmid: 40892136

Protodrilidae is a small family of almost exclusively interstitial annelids that lack parapodia and chaetae and possess a basiepithelial nervous system. This study presents a histological description of Lindrilus flavocapitatus (Uljanin, 1877), a protodrilid species last examined morphologically in the early 20th century, and provides detailed information on the organization of its nervous and sensory systems using histochemical detection of catecholamines (CAs), scanning electron microscopy (SEM), and alpha‐tubulin immunolabelling. The epidermal ciliary structures on the head show a species‐specific distribution pattern, and SEM reveals three types of ciliary sensory structures, similar to those previously described in other protodrilids. Numerous CA‐containing (CAc) cells are found in both central (CNS) and peripheral nervous systems. A spatial correlation between epidermal ciliary structures and CAc cells offers the first direct evidence supporting the sensory function of some known ciliary types and allows hypotheses regarding their sensory modalities. The widespread, mostly diffuse distribution of epidermal CAc cells throughout the trunk, pygidium, and palps suggests a mechanosensory function, although some presumed mechanosensory cells are not catecholaminergic or lack CAs. The presence of CAs in putative phaosomes on the palps also points to a possible role for these neurotransmitters in photoreception. In addition to typical annelid sensory organs such as palpal receptors, nuchal organs, and possible phaosomes, L. flavocapitatus possesses a unique bud‐shaped sensory organ and a dorsal ridge‐like array of receptor cells, both containing CAs. A prominent CAc gastroesophageal ganglion innervating the complex pharyngeal apparatus of L. flavocapitatus is described for the first time in protodrilids. The results reveal a more differentiated neural and sensory organization in protodrilids than previously recognized. Despite its small body size and a relatively low neuron count, L. flavocapitatus possesses additional CNS regions beyond those common to most annelids and a uniquely organized apical sensory organ.

Palecek‐McClung, Amanda M.; Christen, Charles H.; Jain, Dharamdeep; Dhinojwala, Ali; Blob, Richard W.; Schoenfuss, Heiko L.

doi: 10.1002/jmor.70078pmid: 40856173

Hawaiian stream gobies exhibit diverse adhesive abilities that can be used by these fishes to help climb waterfalls. Mucus is recognized as contributing to successful performance in many adhesive systems, but potential specializations of mucus production and composition have not been tested in these fishes. This study examines how anatomical (sucker size and goblet cell density) and biochemical (mucus composition) traits may contribute to adhesive success in climbing gobies. Using histological and spectroscopic analyses, we quantified the density of mucus‐producing goblet cells in adhesive structures (lips and pelvic suckers) and assessed differences in mucus chemistry between the pelvic suckers and the body. Goblet cell density in lips and suckers increased with climbing ability, aligning with species distribution across stream elevations. The non‐climbing Stenogobius hawaiiensis exhibited the lowest goblet cell densities, while the best climbers (Sicyopterus stimpsoni and Lentipes concolor) showed the highest densities. Among inching climbing gobies that use the mouth to climb especially as juveniles, goblet cell density in the lips was, instead, greater in adult individuals. This suggests that mucus production of the lips may have a broader protective role during interactions with rough substrates, rather than a strict relationship with adhesive performance. Infrared spectroscopy of mucus revealed similar chemical signatures in both sucker and caudal peduncle mucus, suggesting that mucus composition does not change across the body to enhance adhesion. These findings indicate that goblet cell density and, thus, enhanced mucus production (rather than compositional changes) may aid the adhesive performance of climbing gobies, contributing to their ecological success. Understanding these adhesive mechanisms from tissue to whole‐animal levels of organization clarifies the specific factors that were specialized during the evolution of the distinctive locomotor behavior of these amphidromous fishes.

Tyler, Seth; Hooge, Matthew; Sterrer, Wolfgang

doi: 10.1002/jmor.70083pmid: 40913011

In live specimens of the nemertodermatidan Flagellophora apelti Faubel and Dörjes, 1978, a peculiar organ looking like a fascicle of bristles—and so called a broom organ by its discoverer—occupies the front third or so of the body. The animal can extrude the organ to splay the bristles in a fan‐like array, each bristle having an adhesive tip. Described first by light histology as a bundle of flagella, this organ can be seen by transmission electron microscopy to be actually a bundle of exceedingly long necks of glands. Bodies of the glands sat well behind the brain, and the necks reached forward through the brain and folded back to a small bulb where they emerged into a canal. Protrusion of the organ would involve unfolding of the necks, projection of the bulb through a pore at the rostral end of the canal, and eversion of the bulb to form a knob‐like point from which the gland necks radiate. Confocal microscopy of specimens stained for F‐actin showed the muscles that drive protrusion and retraction and cell junctions that anchor the necks at the bulb, and we propose mechanisms through which these motions can be produced. The animal's rostrum had many other glands besides those of the broom organ, including a set forming a brush‐like protruberance immediately ventral to the pore of the broom organ, and it likely plays a role in processing prey captured by the broom. Longitudinal muscles of the ventral body wall were specialized into strong bands that could serve to transfer the prey, then, to a facultative mouth.

Zhang, Gui‐Zhi; Yu, Shou‐Guang; He, Ying; Gao, Lei; Jiang, Lu

doi: 10.1002/jmor.70077pmid: 40855962

Mouthparts exhibit diverse morphological features in scarab beetles, resulting from the adaptation to the various living and feeding habits. Adoretini is a small tribe of Rutelinae, remarkable for bearing a beak‐like projection on the labrum. However, the correlation between peculiar structures and feeding habits remain unsatisfactory. In this study, the adult mouthparts of Proagopertha lucidula, Anomala corpulenta, Popillia quadriguttata and Adoretus sinicus were compared using scanning electron microscopy, to investigate the structural basis underlying the distinctive feeding behavior of A. sinicus. Based on our investigation, the adult incisors of A. sinicus could not meet when closed. Instead, a beak‐like labral projection fits precisely between the paired incisors, which is a configuration markedly different from the other three species. Our scanning electron micrographs reveal distinct wear marks on lateral sides of the labral projections and the mesal corners of mandibular incisors, supporting the hypothesis that both structures are involved in the chewing process. These findings help explain the characteristic perforated damage observed on leaves attacked by Ad. sinicus and also provide a potential functional basis for the labral projection unique to adult Adoretini.

Ospina‐Sarria, Jhon Jairo; Ramírez‐Pinilla, Martha Patricia; Grant, Taran

doi: 10.1002/jmor.70086pmid: 40944565

Amphibian testes vary in shape, from multilobed in caecilians and salamanders to compact, ovoid organs in anurans. Although these variations have been studied extensively in amphibians, there has been little investigation into the structural, copulatory, and reproductive behavioral consequences of unpaired testes, a character shared among some amphibians, cyclostomates, and some teleosts. We analyzed the morphology and structure of unpaired testes in Pristimantis fetosus and Pristimantis permixtus. We also report a single testis in P. hernandezi. Our results suggest that the testis arrangement in these species results from the hypertrophy and fusion of two testes rather than the loss or reduction of one testis. Furthermore, the occurrence of germ cells at different stages of development suggests that spermatogenesis is similar to that described for vertebrates, with spermatogonia undergoing mitosis to form spermatocytes, which then undergo meiosis to form spermatids. Like other brachycephaloid frogs, Pristimantis with fused testes exhibit direct development and reproduction on land, but they are the only anurans known to undergo testicular fusion. We propose to recognize the occurrence of fused testes as a unique putative synapomorphy for a new species group distributed in the Colombian Andes, which we refer to as the P. hernandezi species group. A comparative survey among vertebrates reveals no apparent variations in testicular organization, sperm development, or copulative and reproductive behavioral characters associated with the fusion of testes, suggesting that its occurrence might not have functional implications for vertebrate testes. The independently evolved occurrence of fused testes in cyclostomates, teleosts, and amphibians raises an exciting perspective on the study of the molecular origin, evolution, and functional significance of testis variation in vertebrate reproduction and biology.

Jia, Jia; Zhang, Mei‐Hua; Wang, Bin; Bever, Gabriel S.; Fei, Liang; Ye, Chang‐Yuan; Jiang, Jian‐Ping; Gao, Ke‐Qin

doi: 10.1002/jmor.70087pmid: 40995986

An enigmatic salamander species Protohynobius puxiongensis was named 25 years ago but since then has been disputed as a genus and species of its own or a species in the genus Pseudohynobius. Here, we provide a detailed anatomical account for P. puxiongensis based on micro‐CT scans of five specimens, including one larva, one subadult and three adults. For the first time we reveal anatomical details in the braincase, hyobranchium and the postcranial skeleton. Our comparative study with species of Pseudohynobius and Liua clarified previous disputes over the anatomy of the skull, and confirmed that the internasal bone is an intraspecific variation that is present in several hynobiid species. Our study found that P. puxiongensis possesses fundamental morphological features that distinguish this enigmatic salamander from all species in the genus Pseudohynobius; therefore, the results of our study provide evidence to reject the combination of “Pseudohynobius puxiongensis”, and support Protohynobius as the valid generic name for the species in question for the purpose of the Principle of Priority. The extensive morphological disparities between Protohynobius and Pseudohynobius identified herein combined with their relatively short genetic distances recognized by previous studies indicate that these hynobiids have had a high evolutionary rate that may be associated with the intense orogenies around the eastern edge of the Qinghai‐Tibetan Plateau during the Neogene.

Jandausch, Kenny; Straka, Jakub; Kamp, Thomas; Stark, Heiko; Beutel, Rolf G.; Niehuis, Oliver; Pohl, Hans

doi: 10.1002/jmor.70088pmid: 40996083

Females of the insect order Strepsiptera are known to be traumatically inseminated. Traumatic insemination is the process of insemination by sperm transfer through a wound inflicted by the male in the female's integument, rather than by the male transferring sperm through the female's genital opening. Females fertilised by traumatic insemination are likely to exhibit morphological adaptations that help them to reduce the fitness costs associated with the integument wounding. One such adaptation is the presence of a paragenital organ. It has been described in traumatically inseminated bugs of the superfamily Cimicoidea and in species of the Strepsiptera genus Stylops. Although the paragenital organ appears to play a critical role in the mating biology of Stylops species, its phylogenetic roots are unknown. Here, we show that the paragenital organ in Strepsiptera may be an autapomorphy of the family Stylopidae, where we found it present in all species of the genera we studied (i.e., Eurystylops, Halictoxenos, Hylecthrus, Kinzelbachus). Our data thus refute the notion that the paragenital organ in Strepsiptera is exclusive to the genus Stylops. Integument relative thickness assessment based on µCT data revealed that regardless of the presence of a paragenital organ in Strepsiptera, penetration sites in the female's integument are thickened relative to control sites. In addition, we found evidence for the lateral processes of the secondary larval exuvia stabilising the paragenital organ. Our study contributes to the basic understanding of the evolution and the function of the paragenital organ in Strepsiptera and suggests potentially important morphological characters for a species‐level phylogeny of the Stylopidae.

Collin, H. Barry; Ha, Myoung Hoon; Wagner, Alizee; Folwell, Megan; Dunstan, Nathan; Crowe‐Riddell, Jenna; Collin, Shaun P.

doi: 10.1002/jmor.70084pmid: 40927955

Although the surface micro‐ornamentation of the scales within the skin of snakes has been the subject of many previous studies, there has been little work done on the spectacle, a protective (keratinised) goggle separated from the underlying cornea by a sub‐spectacular space. The surface ultrastructure of the “Oberhäutchen” of the spectacle is examined in nine species of snakes (five aquatic and four terrestrial) using light and electron microscopy, micro‐computed tomography and gel‐based profilometry. Significant topographic differences in cell size (increases of between 5.4% and 165% in the periphery), shape (central pentagonal/hexagonal to long peripheral) and density (2579–10,391 cells/mm2 in the centre vs. 2315–4291 cells/mm2 in the periphery) are revealed. Small indentations in the surface (micropits) and/or microholes in the cell membrane decorate the epithelial surface of all species, which also show a centre‐to‐periphery gradient in diameter (42.39–120.55 nm in the centre vs. 63.76–182.60 nm in the periphery). Microridges are found on the superficial cells of the spectacle of only one species (the terrestrial Cantil Viper, Agkistrodon bilineatus) with straight, parallel ridges in the centre (138.4 ± 28.2 nm wide) and a more complex pattern of ridges (143.1 ± 19.1 nm wide) in the periphery. The micro‐ornamentation of the spectacle in both land and sea snakes is compared with those found over the body scales and discussed with respect to a range of potential functions, while still allowing a clear optical pathway for vision.