The family is monotypic.
Clio Linnaeus, 1767:
« Shell conical to triangular, bilaterally symmetrical, straight or dorso-ventrally curved; ventral and dorsal shell parts separated by carinae, protoconch inflated, with or without apical spine; radial, transverse ornamentation present or absent. » – Janssen, Bush & Bednaršek: “The shelled pteropods of the northeast Pacific Ocean (Mollusca: Heterobranchia, Pteropoda)”, Zoosymposia vol.13, Auckland 2019, p.320.
