Rostanga dentacus is a species of sea slug, a dorid nudibranch, a marine gastropod mollusc in the family Discodorididae.

It has subsequently been reported from the Great Barrier Reef, Australia.

[2][3] Rostanga dentacus is a red dorid nudibranch; the dorsum covered with caryophyllidia.

[1] Rostanga dentacus was found on a colony of an unidentified orange sponge.

[1] Most other species of Rostanga feed on sponges of the family Microcionidae.