Morfologia dentária e dimorfismo sexual das raias do gênero Psammobatis Günther, 1870 (Chondrichthyes: Batomorphii: Arhynchobatidae) do Sul do Brasil, Atlântico Sul Ocidental

Abstract

The genus Psammobatis Günther includes eight species: P. bergi Marini, P. extenta (Garman), P. lentiginosa McEachran, P. maculatus Hildebrand, P. normani McEachran, P. parvacauda McEachran, P. rudis Günther – type-species, and P. rutrum Jordan. Psammobatis bergi, P. extenta, P. lentiginosa, and P. rutrum are found in the Atlantic coast of Brazil from Rio de Janeiro to Rio Grande do Sul states. Studies on dental morphology may contribute not only to the biological knowledge of the species involved, but also to their taxonomy and phylogenetic relationships. The purpose of this study is to characterize the dental morphology of Psammobatis extenta, P. lentiginosa and P. rutrum and aims to verify whether there is sexual and/or ontogenetic heterodonty. The specimens were captured in depths between 40m and 145m in the coasts of Rio Grande do Sul and Rio de Janeiro states, and deposited at Fundação Universidade do Rio Grande and Universidade do Estado do Rio de Janeiro. Twenty-seven dental arches were examined. The jaws were detached from the body, and three regions (two lateral and one symphyseal) from each individual were photographed using a scanning electron microscope (SEM). Tooth were measured and compared between adult males and adult females of the three species, and also among immatures of P. extenta. Adult females of the three species showed pavement-like dentition, with flat, smooth, monocuspidate teeth (crusher type); the crown had a diamond shape, with the symphyseal teeth slightly larger than the others. The teeth of adult males of the three species, although also monocuspidate and diamond-shaped crown, have a longer, sharp cusp (grabber type) than females. Additionally, teeth observed on males were point inward in the symphysis region and sideward (with shorter but still pronounced cusp) in the distal region. The longest cusps in adult males of P. extenta are smooth and showed a circular shape, based on its external format; while males of P. rutrum and P. lentiginosa have an elliptical shape. P. lentiginosa presented a slight groove in the middle of the cusp. In Psammobatis extenta, the only species with immature specimens available, no sexual dimorphism related to dentition was observed. Similar to adult females, they have pavement-like dentition with the crusher type teeth; but without variation of size between the symphysis teeth and the others.