Anatomical Description of Scapulocoracoid and Gill Arches of Benthobatis kreffti

Univ. Sci. 2015, Vol. 20 (3): 305-312 doi: 10.11144/Javeriana.SC20-3.adsg Freely available on line review article Anatomical Description of Scapulocoracoid and Gill Arches of Benthobatis kreffti Ítalo Rafael Bini Junior 1 , Camila Mayumi Hirata dos Santos 1,2, Otto Bismarck Fazzano Gadig1 Abstract This study describes the scapulocoracoid and the ventral gill arches of a rare benthic elasmobranch, Benthobatis kreffti, based on specimens collected at depth of 500 m off the coast of São Paulo state, southern Brazil. The scapulocoracoid has an anterior fontanelle that is placed laterally. Condyles are similar in size, unequally spaced, and they are not aligned horizontally. The mesocondyle is located below the other condyles. The posterior fenestrae are allocated within the cartilage of the scapulocoracoid, while the anterior fenestrae cross its lateral-posterior segment. The suprascapula is arched posteriorly, and it is not connected or fused to the synarcual or the vertebral column. Three unfused hypobranchial elements were found in the ventral gill arches. The ceratobranchials are rod-like shaped, with fenestrae from first to fourth ceratobranchials. The fifth is morphologically distinct and connected to the scapulocoracoid. There is a pair of elements above the basibranchial copula, of unknown origin, also reported for other congeneric species, Benthobatis marcida. Such character could represent an autapomorphy of the genus. Keywords: anatomy, skeleton, electric ray, Torpediniformes; Chondrichthyes Introduction Edited by Juan Carlos Salcedo-Reyes & Andrés Felipe Navia 1. Laboratório de Pesquisa de Elasmobrânquios, Universidade Estadual Paulista “Júlio de Mesquita Filho” Campus Experimental do Litoral Paulista, Praça Infante Dom Henrique, s/n, São Vicente/SP, Brasil 2. Universidade Estadual Paulista “Júlio de Mesquita Filho”, Campus de Rio Claro, Avenisa 24A, 1515, Rio Claro/SP, Brasil. Received: 02-12-2014 Accepted: 08-05-2015 Published on line: 29-05-2015 Citation: Bini IRJ, Santos CMH, Gadig OBF (2015) Anatomical Description of Scapulocoracoid and Gill Arches of Benthobatis kreffti. Universitas Scientiarum 20(3): 305-312 doi: 10.11144/Javeriana.SC20-3.adsg Funding: Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq. Electronic supplementary material: N/A The batoid fishes (rays, skates, guitarfishes and sawfishes) represent approximately 54 % (630 in 1170) of all Chondrichthyes species (Aschliman et al. 2012). The numbfishes (Narcinidae, Torpediniformes) consist of four genera and about 18 species of small to medium sized benthic elasmobranchs with electric organs in the disc (McEachran & Carvalho 2002). The so-called blind electric rays, genus Benthobatis, are known by four deep sea species, and they share the remarkable feature of vestigial and non-functional eyes (Carvalho 1996b). Benthobatis kreffti Rincón, Stehman & Vooren 2001 is the smallest electric ray species (about 300mm total length – TL), it was described based on specimens caught along the southern Brazilian continental slope at depths between 400 and 600 meters (Rincón 1997, Rincón et al. 2001). Due to the scarcity of collected specimens, its biological and natural history data are Universitas Scientiarum, Journal of the Faculty of Sciences, Pontificia Universidad Javeriana, is licensed under the Creative Commons Attribution 4.0 International Public License 306 Anatomy of Benthobatis kreffti virtually unknown and most of the information comes from the original description (Rincón et al. 2001). Any anatomical approach in the study of electric rays is important to elucidate the interrelationships among its representatives, as well as within the general batoid phylogeny, since there is a historical disagreement in the phylogenetic position of Torpediniformes, regarded as a basal lineage (Nishida 1990, McEachran et al. 1996, McEachran & Aschliman 2004) or derived in relation to Rhinobatiformes (Shirai 1996). Elasmobranch skeletal analysis are a useful tool for taxonomy and systematics studies, remarkably those involving the neurocranium, gill arches, scapulocoracoid, pelvic girdle, clasper, and synarcual (Hubbs et al. 1968, Compagno 1977, McEachran 1983, Miyake & McEachran 1991). Out of the five characteristics that support Torpediniformes as a group, three of them involve the skeleton (Claeson 2014). Regarding the genus Benthobatis, there is available information on the neurocranium, hyomandibula, branchial arches, scapulocoracoid, propterygium, synarcual, pelvic girdle and clasper (Carvalho 1999a, Rincón et al. 2001, Carvalho et al. 2003, Claeson 2014). However, for Benthobatis kreffti there are no descriptive data for the ventral gill arches and the scapulocoracoid, and the present study intends to complement the anatomical information of the species, through the analysis and comparison of these structures. Materials and Methods The analysis was based on 10 adult specimens of Benthobatis kreffti (five 206 mm to 245 mm TL males; five 228 mm to 251 mm TL females) caught at 500 m deep bottom trawls during research cruise carried out by the Universidade Estadual Paulista (UNESP) along the São Paulo state coast, southern Brazil, between July 31 to August 2, 2003. The species identification was based on Rincón et al. (2001). After formalin fixation and alcohol preservation, the specimens had their skin, muscles and connective tissue removed by a dissection procedure, exposing the scapulocoracoid cartilage and gill arches, a stereomicroscope was employed for this process. The Fig. 1. Dorsal view of the pterygia region of Benthobatis kreffti in A. the plate in B. and an outline of the animal in C. Propterygium (PPG); mesopterygium (MSG); and metapterygium (MTG); electric organ (EO) and the dashed line is the level of suprascapula. Universitas Scientiarum Vol. 20 (3): 305-312 http://ciencias.javeriana.edu.co/investigacion/universitas-scientiarum 307 Bini et al. skeletal terminology follows Miyake & McEachran (1991) and McEachran et al. (1996). Results Scapulocoracoid: It is the skeletal structure that supports the pectoral fins through the articulation of the condyles with the pterygia. The propterygium (PPG) is tubular and rectilinear in shape, and extends to the level of suprascapula (Figure 1). The mesopterygium (MSG) is flat, rectangular in shape, and shorter than the others, while the metapterygium (MTG) is flat, triangular in shape, and widest in its anterior region (Figure 1). The scapulocoracoid has two bar-like structures, both are arched and have thin and delicate cartilage. The dorsal one, the suprascapula (SS), is posteriorly bowed (Figure 2) and not connected or fused to the synarcual or the vertebral column (Figure 1); the ventral one, the coracoid bar (CB) is anteriorly bowed. The anterior fontanelle (AF) is triangular and laterally positioned (Figure 3). The lateral-posterior segment is extensive and its posterior region has the condyles and fenestrae (Figur (...truncated)