Fiona is a genus of sea slugs, specifically aeolid nudibranchs, marine gastropod molluscs in the family Fionidae. Fiona is the type genus of the family Fionidae.
Species within the genus Fiona include:
A study published in 2016 showed that Fiona pinnata is a species complex of at least three species.
Species of Fiona feed on goose barnacles and live on floating objects in the oceans worldwide.