Rostanga dentacus is one of the few species of Rostanga with horizontally arranged lamellae on the rhinophore club.
The shape of the radular teeth is unique with all but the innermost tooth having long pointed non-denticulate cusps. The elongate innermost tooth has a few long pointed inner denticles. The name dentacus (Latin: dentis = tooth; acus = needle) refers to the shape of the teeth.
At present the species is known from Hong Kong and the Great Barrier Reef, Queensland, suggesting a wide distribution, at least in the western Pacific.