Phylogenetic significance of clasper morphology of electric rays (Chondrichthyes: Batoidea: Torpediniformes).

Torpediniformes (electric rays) is a monophyletic group strongly supported by morphological and molecular phylogenetic studies. The claspers of electric rays, however, are poorly documented in comparation to the clasper of other batoids, especially skates, and the knowledge of their anatomical variation is restricted to the description of a few species. The present article analyzes the external and skeletal clasper anatomy of electric rays and reports newly discovered characters that can be useful for taxonomic diagnoses and higher-level systematic studies. The family Torpedinidae exclusively presents the integumental flap, a poorly calcified clasper skeleton, and a dorsal marginal cartilage with a medial flange on its distal portion. Derived or diagnostic characters were not found in the clasper of the reportedly nonmonophyletic families Narcinidae and Narkidae; however, the claspers of species and genera of narcinids and narkids present different anatomical patterns that can be useful for taxonomic and phylogenetic studies.

Taxonomy and morphology of the skate genus Atlantoraja (Rajiformes: Arhynchobatidae)

Abstract The skate genus Atlantoraja is composed of three species (A. castelnaui, A. cyclophora, and A. platana) which differ from the other Riorajini species, Rioraja agassizii, in regards to their clasper features, squamation and presence of a caudal fin. Despite of being distributed along Southwestern Atlantic and commonly captured by fisheries in Brazil, Uruguay and Argentina, detailed accounts on external and internal morphology are scarce and the taxonomic status of Atlantoraja species was not revised so far. The aim of this study, therefore, is to review the taxonomy of the genus Atlantoraja, updating information on type specimens and clarifying misidentifications among species, and to describe in detail anatomical structures such as neurocranium, visceral arches, pelvic girdle, dermal denticles and teeth. Lectotypes and paralectotypes are designated for Atlantoraja castelnaui and A. cyclophora. Notes on intraspecific variation within species are also provided. Atlantoraja cyclophora and A. platana are more similar to each other than to A. castelnaui in regards to the squamation (body dorsal surface smooth vs. densely covered by prickles) and color pattern of body dorsal surface, position of orbital foramina, overall shape of neucrocranium and body measurements. Lastly, we discuss the morphological differences among species of Atlantoraja and recommend the inclusion of characters presented here in future cladistic analyses.

Resumo O gênero Atlantoraja é composto por três espécies (A. castelnaui, A. cyclophora e A. platana), as quais diferem da outra espécie da tribo Riorajini, Rioraja agassizii, em relação a características do clásper, escamas e presença de uma nadadeira caudal. Apesar de serem distribuídas ao longo do Atlântico Sul Ocidental e serem comumente capturadas em atividades pesqueiras do Brasil, Uruguai e Argentina, descrições detalhadas sobre a morfologia externa e interna são escassas e o status taxonômico das espécies de Atlantoraja não foi revisado até então. O presente estudo tem como objetivos: revisar a taxonomia do gênero Atlantoraja, atualizando as informações sobre espécimes-tipo e elucidando erros de identificação entre as espécies, e descrever estruturas anatômicas, tais como neurocrânio, arcos viscerais, cintura pélvica, dentículos dérmicos e dentes. Lectótipos e paralectótipos são designados para Atlantoraja castelnaui e A. cyclophora. Notas sobre a variação intraespecífica em cada espécie também são fornecidas. Atlantoraja cyclophora e A. platana são mais similares entre si do que A. castelnaui em relação às escamas (superfície dorsal do corpo lisa vs. densamente coberta por dentículos dérmicos), padrão de colorido da superfície dorsal do corpo, posição dos forâmens orbitais, formato geral do neurocrânio e medidas corpóreas. Por fim, comparações morfológicas entre as espécies de Atlantoraja são realizadas, recomendando-se a inclusão dos caracteres aqui apresentados em análises cladísticas futuras.

Redescription of the Rio skate Rioraja agassizii (Rajiformes: Arhynchobatidae) with notes on internal anatomy and intraspecific variation

Rioraja agassizii belongs to the monotypic genus Rioraja and differs from the other Riorajini species of the genus Atlantoraja by the shape of anterior nasal flap, squamation, clasper skeleton, body measurements and color pattern. Although R. agassizii is a well-known species, commonly captured in inshore waters of the southwestern Atlantic, its external morphology and internal anatomy have never been fully described and little is known on intraspecific variation within the species. Juvenile and adult, male and female specimens were examined, measured and dissected. Herein, we redescribe the species and present detailed descriptions and illustrations of external morphology, neurocranium, jaws, hyoid and gill arches, and pelvic fin and girdle. Additionally, notes on sexual dimorphism and ontogenetic differences in coloration, body and cranial measurements, and dermal denticles are provided.(AU)

Rioraja agassizii pertence ao gênero monotípico Rioraja e difere das demais espécies da tribo Riorajini classificadas no gênero Atlantoraja pelo formato da aba nasal anterior, escamas, esqueleto do clásper, medidas corpóreas e padrão de coloração. Embora R. agassizii seja uma espécie bem conhecida, comumente capturada em águas costeiras do Atlântico Sul Ocidental, sua morfologia externa e anatomia interna não foram totalmente descritas e pouco se sabe sobre a variação intraespecífica nesta espécie. Espécimes juvenis, adultos, machos e fêmeas foram examinados, medidos e dissecados. Neste estudo, a espécie é redescrita e descrições detalhadas e ilustrações da morfologia externa, neurocrânio, maxilas, arcos hioide e branquiais, nadadeira e cintura pélvicas são apresentadas. Adicionalmente, notas sobre dimorfismo sexual e variação ontogenética na coloração, medidas corpóreas e craniais, e dentículos dérmicos são fornecidas.(AU)

Clasper Morphology of the Japanese Sawshark, Pristiophorus japonicus Günther, 1870 (Chondrichthyes: Elasmobranchii).

Sawsharks (Pristiophoriformes) are slender, medium-sized sharks with elongated, saw-like snouts, and include the monotypic Pliotrema and Pristiophorus with seven species. The phylogenetic position of sawsharks is still problematic as phylogenetic hypotheses based on morphological and molecular evidence disagree about their relationships, whether closer to batoids (morphological data) or grouped with squaliforms, angelsharks, and hexanchiforms in an all shark higher taxon (molecular data). However, many aspects of the morphology of sawsharks are poorly known. The present article describes the clasper musculature and skeleton of a sawshark (Pristiophorus japonicus); the clasper skeleton of a sawshark is described for the first time. The clasper musculature is similar to squaliforms and most batoids, whereas the clasper skeleton is similar to that found in Squatina and Squalus. However, the ventral marginal, dorsal terminal (dt), and ventral terminal cartilages are distinct and diagnostic at least for Pristiophorus japonicus. Comparisons with galeomorph sharks are necessary to further refine our conclusions in relation to the systematic significance of the clasper muscles and skeleton of the Japanese sawshark. Anat Rec, 302:1666-1670, 2019. © 2019 American Association for Anatomy.

Morphology of the clasper musculature in rays (Chondrichthyes; Elasmobranchii: Batoidea), with comments on their phylogenetic interrelationships.

The subclass Batoidea comprise skates, electric rays, stingrays, guitarfishes, and sawfishes, and their interrelationships are still problematical despite recent morphological and molecular phylogenetic studies. The most recent morphological phylogeny indicates that guitarfishes are a polyphyletic group, and that the phylogenetic placement of Platyrhina and Platyrhinoidis is still unclear. Several molecular studies suggest that guitarfishes (except Zanobatus) and sawfishes comprise the monophyletic order Rhinopristiformes, and that thornback rays (Platyrhinidae, Platyrhina, and Platyrhinoidis) are more closely related to the electric rays (Torpediniformes); rhinopristiforms have recently been supported by morphological data as well. The clasper musculature of batoids suggests an alternative pattern of interrelationships for thornback rays, with the m. dilatator attached to the dorsal terminal 1 cartilage by a series of tendons found only in Rhinopristiformes and Platyrhinidae, suggesting that they are closely related. Furthermore, Rajiformes, Rhinopristiformes, and Platyrhinidae exclusively share a reduced m. extensor lateralis, suggesting that these taxa form a monophyletic group. This study identifies new synapomorphies that corroborate the separate monophyly of Rajiformes, Torpediniformes, and Myliobatiformes: the m. dilatator divided into dorsal and ventral bundles and the presence of a single m. flexor are found only in Rajiformes; the extensor lateralis with a laminar shape is a derived character of Torpediniformes; and the exclusive m. flexor medialis arising on the puboischiadic bar is derived for Myliobatiformes.

Comparative anatomy of the clasper of the subfamily Potamotrygoninae (Chondrichthyes: Myliobatiformes).

Claspers of stingrays (Myliobatiformes) are poorly documented in comparison to claspers of skates, with our knowledge restricted mainly to external morphological characters and skeletal components included in descriptions of new species; more encompassing morphological comparative analyses are lacking. Concerning potamotrygonins, clasper morphology has been described for a handful of species, but without elucidating their variation and systematic potential. The present article analyzed clasper structures in all genera of the subfamily Potamotrygoninae (Potamotrygon, Paratrygon, Plesiotrygon, and Heliotrygon), which were compared to the clasper of Styracura and some dasyatid genera. Potamotrygon shows some morphometric variation among the species analyzed. Anatomically, we found variation mainly in the dorsal terminal 1 and accessory terminal 1 cartilages, which are considered diagnostic among potamotrygonin genera; external morphological structures did not present significant differences among potamotrygonins.

Clasper morphology of skates of the tribe Riorajini (Chondrichthyes: Rajiformes: Arhynchobatidae) and its systematic significance.

Claspers of adult specimens of the skate tribe Riorajini, family Arhynchobatidae, comprising Atlantoraja and Rioraja, are described, compared, and systematically reinterpreted based on material collected off southeastern and southern Brazil. For the first time the external components and musculature of the clasper of members of this tribe are described and related to internal (skeletal) structures. The component pecten is present in all species of Atlantoraja but absent in Rioraja. The new external component grip, an autapomorphy of A. cyclophora fully developed in adults, is described. Rioraja presents dorsal terminals 1 and 2, ventral marginal distally extended and ventral terminal cartilages. Dorsal terminals 1 and 2, ventral marginal distally extended, accessory terminals 2 and 3, and ventral terminal cartilages occur in Atlantoraja. A new interpretation of the ventral marginal distally extended is discussed. The dorsal terminal 1 of Atlantoraja has an inverted U shape but is triangular in Rioraja. The accessory terminal 2 cartilage is reported for the first time in Atlantoraja cyclophora. The accessory terminal 3 is present only in A. platana and A. cyclophora, and absent in Rioraja and A. castelnaui. Many of our findings concerning the clasper skeleton do not agree with previous interpretations. The arrangement, distribution and systematic significance of many of the terminal clasper components are discussed among rajoids.