Fiona pinnata
(Eschscholtz, 1831)

Family: Fionidae


Worldwide distribution on floating objects


Eden, southern New South Wales, Australia. February 1983, AM C137996. On Lepas sp attached to driftwood. Inset showing undulating 'gill' along cerata. Note white anal papillae midway down body in lower photos. PHOTOS: Bill Rudman.

The family is based on this single species. It grows to about 20mm long and lives exclusively on floating objects in the sea, usually feeding on goose barnacles (Lepas spp.) but it has been reported by M.C.Miller to feed on floating cnidarians such as Physalia and Velella. The rhinophores are smooth and the cerata are arranged irregularly along eacg side of the body without any clear clustering or obvious sytem of rows. The cerata lack cnidosacs and are unique in having an undulating 'fin' or 'gill' along the postero-dorsal edge. The anus opens dorsally on the right side, about midway down the body just inside the cerata. Although often described as pelagic, Fiona is unable to swim, and from metamorphosis, lives on floating objects. It usually metamorphoses on goose barnacles. Large populations and their egg masses can often be found associated with colonies of goose barnacles on driftwood, fishing floats. They can also be found on small objects such as Sepia 'cuttlebones' and even Spirula shells - anything on which goose barnacles can live.

Authorship details
Rudman, W.B., 2002 (June 18) Fiona pinnata (Eschscholtz, 1831). [In] Sea Slug Forum. Australian Museum, Sydney. Available from

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