There are six valid species in the traditional genus Bathydoris, all of them found in polar or deep waters: Bathydoris abyssorum Bergh, 1884 (from the deep equatorial Pacific Ocean), Bathydoris ingolfiana Bergh, 1899 (from Greenland), Bathydoris hodgsoni Eliot, 1907 (from Antarctic and subantarctic waters), Bathydoris clavigera Thiele, 1912 (from the Argentinean deep-sea basin and Antarctica), Bathydoris aioca Ev. Marcus and Er. Marcus, 1962 (from deep waters off California), and a new species, Bathydoris spiralis (from deep waters off New Caledonia). Bathydoris patagonica Kaiser, 1980 and Bathydoris violacea Baranets, 1993 are regarded as synonyms of B. hodgsoni and B. clavigera, respectively. Bathydoris spiralis is clearly distinguishable from other members of the genus mainly in having a triaulic reproductive system and a very elongated, spirally coiled deferent duct. Examination of the holotype of B. violacea revealed that it is a synonym of B. clavigera. Bathydoris vitjazi Minichev, 1969 is most likely a synonym of B. hodgsoni, but is provisionally regarded as nomen dubium until more material becomes available. The phylogenetic hypothesis supports the monophyly of the Anthobranchia but shows that the genus Bathydoris is paraphyletic. Species of Bathydoris are divided into two clades, one of them also containing the phanerobranch and cryptobranch dorids. Bathydoris type species B. abyssorum retains its name and diagnosis, but B. clavigera and B. spiralis are excluded from this genus. They are, however, provisionally maintained in "Bathydoris" s.l., a likely paraphyletic group. This result shows some incongruities between the traditional nomenclatural system and phylogenetic systematics.
