Fiona pinnata is a small nudibranch found exclusively on
floating objects (wood or plastics) inhabited by goose
barnacles (Lepas sp.). It is an unusual nudibranch both in
its ecological niche selection and its anatomy.
Propodial tentacles: Absent, (foot rounded). Oral tentacles: 2 in number, medium, white. Rhinophores: White, smooth. Cerata: Brownish coloured, without white tips (Cnidosacs
absent). Body: White, with hints of orange brown on dorsum and
blotches between the rhinophores. Foot: White without appendages.
Size range: 4-16mm. Common in its niche.
Specific characteristics: This species is easily identified
in the field. It is always found on floating debris with
Lepas sp., the colour of the ceras is a drab brown to dark
brown without cnidosacs and the sail-like projections on
the cerata, which are unique to this species.