The systematics of the stingray genus Urotrygon with comments on the interrelationships within Urolophidae (Chondrichthyes, Myliobatiformes)

Typescript (photocopy).The species of the stingray genus Urotrygon were investigated to elucidate the species composition and to clarify the systematic status of the nomical genera Urotrygon and Urolophus (Urolophidae) within Myliobatiformes. Specimens of all nominal species were compared morphometrically by Principal Component Analysis, meristically by univariate analysis and according to their pattern of squamation. These analyses suggested that there are ten valid species of Urotrygon: Urotrygon daviesi, U. microohthalmum. U. venezuelae. H. munda, U. sp (1), U. sp (2), U. rogersi, U. chilensis. II. sp (3) and U. aspidura. Urotrygon binghami is considered a junior synonym of U. rogersi. Urotrygon asterias, U. serrula, U. peruana. U. caudispinosa and U. goodei are considered synonyms of U. chilensis. The anatomical comparisons of morphological characters, i.e., cranial and visceral skeleton, cranial and visceral musculature, cranial nervous and vascular systems, pectoral and pelvic girdles and clasper skeleton, were made among most of the nominal genera of batoid fishes (sawfishes, guitarfishes, skates, electric rays and stingrays) to elucidate the systematic status of Urotrygon and Urolophus within Myliobatiformes. The following conclusions can be drawn from the present study: 1) Urotrygon daviesi should be removed from the genus Urotrygon and regarded as incertae sedis within Myliobatiformes. The characters which distinguish U. daviesi from the remaining species of Urotrygon represent either primitive character states, homoplastic character states or character states of unknown polarity. 2) Urotrygon excluding U. daviesi is defined by one synapomorphy, the presence of the X -cartilage closely associated with the β-cartilage. 3) Amphi-American Urolophus are provisionally considered monophyletic, distinct from the Australian-western Pacific Urolophus and the genus Urobatis is resurrected for them. Urobatis and Urotrygon except U. daviesi possess one putative synapomorphy, an embryonic spiracular fold. 4) Australian-western Pacific Urolophus possess one putative synapomorphy, the presence of a large foramen for the n. opticus. 5). There are no known synapomorphies shared by the three nominal genera of Urolophidae, Urobatis, Urolophus and Urotrygon, and thus the systematic status of Urolophidae remains uncertain..