Thalassopterus zancleus is a species of swimming sea slug, a shell-less pelagic marine opisthobranch gastropod mollusk in the family Clionidae.

[2] Thalassopterus zancleus is the only species in the monotypic genus Thalassopterus.

It is known only from juveniles stages.

[3] Adults have not yet been found.

This Clionidae-related article is a stub.