Description: The thin, transparent shell is internal and is about half the body length, which may reach 60 mm. Pale lemon yellow to orange in colour, often with net-like markings in the middle of the smooth dorsal mantle. A gill is present on the right-hand side of the body, concealed between the mantle and the foot. The skin can secrete defensive sulphuric acid if attacked. The appearance of this sea slug appears to be providing camouflage on Oscarella, with a central transparent patch mimicking an oscule of the sponge and the reticulate pattern looking similar to lobules of the sponge.

Habitat: Feeds on the sponge Oscarella sp. Normally found beneath rocks on the lower shore, but can be found down to 30 m depths on steep rock faces or hard substrata.

Distribution: Common around Britain and Ireland.

Similar Species: Berthellina citrina has been recorded from Britain but it is more likely that these records refer to Berthellina edwardsii or possibly Berthellina aurantica.

Key Identification Features:

• Mantle extends over the head and the rhinophore bases.
• Yellow mantle and characteristic mottling.

Distribution Map from NBN: Berthella plumula at National Biodiversity Network mapping facility, data for UK.

iNaturalist: Berthella plumula at iNaturalist World Species Observations database.

GBIF data for Berthella plumula

WoRMS: Berthella plumula at World Register of Marine Species. Accepted name: Berthella plumula (Montagu, 1803). AphiaID: 140812.

Classification: Biota; Animalia; Mollusca; Gastropoda; Heterobranchia; Euthyneura; Ringipleura; Nudipleura; Pleurobranchida; Pleurobranchoidea; Pleurobranchidae; Berthella