Berthella plumula from the British Isles

January 5, 2002
From: Bernard Picton

Hi Bill,
Checking through the Forum today I see that you don't have much on Berthella plumula, so here are some photos and information. It is the type species of Berthella, described in 1803 by Montagu. It is a common species around the British Isles and extending from Norway to the Mediterranean. It is normally found beneath rocks on the lower shore but I have seen it frequently at St. Kilda on the west coast of Scotland down to depths of 30m. on steep rock faces. It seems to feed on the sponge Oscarella lobularis and the appearance of Berthella seems 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. I have illustrated this is in a separate message

Photos are from St. Kilda, Scotland, July, 1984 and August 1985.

Bernard Picton

Picton, B.E., 2002 (Jan 5) Berthella plumula from the British Isles. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Thanks Bernard,
Bill Rudman

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