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)

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.

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.

Taxonomic review of catsharks of the Scyliorhinus haeckelii group, with the description of a new species (Chondrichthyes: Carcharhiniformes: Scyliorhinidae).

Sharks of the genus Scyliorhinus from the southwestern Atlantic are reviewed; identification problems and taxonomic misinformation given in the literature are rectified. After extensive examination of the external and internal morphology of specimens collected mostly off southeastern and southern Brazil, Scyliorhinus besnardi Springer & Sadowsky, 1970 is placed in the synonymy of S. haeckelii (Miranda Ribeiro, 1907), which is thoroughly redescribed. Additionally, a new species, Scyliorhinus cabofriensis, sp. nov., is described from the state of Rio de Janeiro, distinguished from all southwestern Atlantic congeners by its color pattern, clasper and neurocranial morphology, and proportional measurements. A key to Scyliorhinus species occurring in the southwestern Atlantic is also provided.

Taxonomy and morphology of species of the genus Squalus Linnaeus, 1758 from the Southwestern Atlantic Ocean (Chondrichthyes: Squaliformes: Squalidae).

Squalus is a genus of reportedly cosmopolitan shark species that have a high taxonomic complexity due to difficulties in their morphological differentiation; many of its species need revision. Currently, there are 26 valid species of Squalus, which have been divided into three species-groups according to overall morphological similarity, the S. acanthias, S. megalops, and S. mitsukurii groups. Loss of type specimens, propagation of erroneous identifications in the literature, and difficulties in obtaining representative series for comparison are secondary challenges that have impeded a global taxonomic revision of the genus. This problem applies clearly to species from the Southwestern Atlantic Ocean, including species that occur off Brazil. Following a current global tendency, a regional taxonomic revision of Squalus was conducted in order to investigate which species are valid in the Southwestern Atlantic Ocean and provide diagnostic morphological characters that can be efficiently used for identifying species. Comparative detailed analysis of external (e.g. morphometrics, dentition, and color pattern) and skeletal morphology (primarily meristic data, neurocrania and claspers) of specimens of Squalus from the region revealed four new species that are herein described (S. albicaudus sp. nov., S. bahiensis sp. nov., S. lobularis sp. nov., and S. quasimodo sp. nov.), as well as S. acanthias, which is redescribed from the region based on new material. Comparisons are offered based on examinations of congeneric species; this work is part of a global systematic revision of Squalus.

Scyliorhinus ugoi, a new species of catshark from Brazil (Chondrichthyes: Carcharhiniformes: Scyliorhinidae).

A new species of catshark (Carcharhiniformes, Scyliorhinidae), Scyliorhinus ugoi sp. nov., is described from off Northeastern and Southeastern Brazil. The new species is closest to the Scyliorhinus haeckelii/besnardi group and S. hesperius but differs in background coloration, head width, sexual maturity, and in cranial and body proportions.