Phyllidiopsis is a genus of sea slugs, dorid nudibranchs, shell-less marine gastropod molluscs and is the largest genus within the family Phyllidiidae.

[1] The species in this genus differ from the other genera in this family by possessing an elongate foregut and fused oral tentacles.

[2] These nudibranchs can be found in the tropical Indo-Pacific region, the eastern Pacific region, in the Red Sea, in the Caribbean Sea and a few in the Northwest Atlantic Ocean.

Among these deep-water sea slugs, there is a group of white species, lacking all contrasting colors.

[3][4] There are presently about 30 species in the genus Phyllidiopsis including :[1] A maximum-parsimony analysis of the nucleotide sequence of the 16S mtDNA gene, performed in 2003, has shown that the genus Phyllidiopsis is paraphyletic.