Dermal denticle variations on a newborn Roughskin Dogfish Centroscymnus owstonii (Chondrichthyes: Somniosidae) captured off northeastern Brazil with notes on ontogenetic differentiation

Abstract

The Roughskin Dogfish Centroscymnus owstonii is a poorly known species with eventual records along the Western South Atlantic. Different dermal denticles have been historically reported for juveniles and adults, which presupposes changes from a juvenile denticle type to an adult denticle type during growth. The present study was based on a male neonate 324 mm in total length (TL) captured with crab pots on the northeastern continental slope of Brazil, between 400–450 meters. This was considered a newborn based on its small size, very similar to previously reported large embryo dimensions and close to the expected birth size in literature. Three different dermal denticles were observed, alternating from the rostrum to the branchial slits, where a tricuspidated denticle type extended covering the rest of the posterior portion of the body. Dermal denticle types and distribution suggest that the replacement process of dermal denticles begins before birth or early after birth, undergoing at least three changes until reaching the adult dermal denticle type. These different types may be related to uterine epithelial histotroph absorption or embryo movement within the mucous environment, which would be enhanced by largely spaced denticles. The reported fragmented distribution of this species along the Brazilian coast is probably related to insufficient sampling coverage.