Phanerobranchia is one of the three major traditional groups of dorid nudibranchs. They are charcterized by lacking a pocket into which the gill can be retracted. No synapomorphies have been yet identified for Phanerobranchia, which probably is paraphyletic. These nudibranchs feed on other marine invertebrates such as bryozoans, ascidians, polychaete worms and other opistobranchs.