The genus Clio is a taxonomic group of small floating sea snails, pelagic marine opisthobranch gastropod mollusks, the sole genus belonging to the family Cliidae[1] All species within this genus exhibit a bilaterally symmetrical shell that is either straight or slightly curved dorso-ventrally towards the apex.

The shell cross-section is elliptical to triangular.

The protoconch is distinct and globular or elliptical, often bearing a spine at its tip.

While some species are classified within subgenera (e.g., Clio s.str., Balantium Bellardi, 1872, Bellardiclio Janssen, 2004), the majority of species remain unassigned to one of these.

Recognised extant species are: Formae: The true status of these formae has to be evaluated, they might be real formae, subspecies, or even species.