Molecular and morphological characterization, phylogenetic affinities and new records of Trypanorhyncha (Cestoda) from the Mexican Atlantic.

During a parasitological survey of elasmobranchs of the Atlantic Ocean on the Mexican coast, the digestive tract of some specimens of the southern stingray, Hypanus americanus (Hildebrand & Schroeder, 1928), and the Atlantic sharpnose shark, Rhizoprionodon terraenovae (Richardson, 1836), were analyzed for tapeworms. These elasmobranchs were obtained from commercial fishing in four localities. Five taxa of Trypanorhyncha were recovered: Kotorella pronosoma (Stossich, 1901) Euzet & Radujkovic, 1989, Oncomegas wageneri (Linton, 1890) Dollfus, 1929, Pterobothrium kingstoni Campbell & Beveridge, 1996, and Pterobothrium sp., from H. americanus, and Callitetrarhynchus gracilis (Rudolphi, 1819) Pintner, 1931, from R. terraenovae. The morphology of collected parasite specimens was characterized based on light and scanning electron microscopy observations; sequences of nuclear large subunit (28S ribosomal DNA gene), nuclear small subunit (18S ribosomal DNA gene) and mitochondrial cytochrome c oxidase subunit I (COI) were obtained and used to infer their phylogenetic affinities. In the phylogenetic hypothesis presented herein (based on 18S rDNA and 28SrDNA), species of Pterobothrium do not form a monophyletic group, K. pronosoma appears to be a complex of cryptic species and their phylogenetic position remains controversial. Concerning C. gracilis, sequence divergence and phylogenetic position of the specimens collected in this study suggest the existence of more than one species. Finally, O. wageneri nested with all previous sequences generated for this species obtained from the Mexican Atlantic coast.