Members of the quite common and diverse copepod family Splanchnotrophidae are specialised endoparasites of shell-less opistobranch gastropod hosts. Another less well-known group of endoparasites also infesting opistobranch sea slugs is the genus Briarella Bergh, 1876 that is currently placed within the Philoblennidae.
A new species of Briarella from Queensland, Australia, infesting the chromodorid nudibranch Ceratosoma trilobatum Gray, 1827 is described using scanning electron microscopy (SEM). The new species differs from the four currently known species Briarella microcephala Bergh, 1876, Briarella risbeci Monod, 1928, Briarella disphaerocephala Monod & Dollfus, 1932, and the unnamed Briarella sp. Bergh, 1876, by having a stocky rather than a vermiform body and longer lateral processes. Of all the members of this genus, Briarella doliaris most resembles splanchnotrophids due to the stocky body. It is thus possible, that Briarella and the Splanchnotrophidae share a common ancestor which switched to an endoparasitic lifestyle. If so, Briarella doliaris could represent the most basal offshoot of a clade of secondarily vermiform Briarella species, or it could be a direct sister taxon to splanchnotrophids, rendering the genus Briarella paraphyletic.