Up to 27mm long.
Mantle reduced, unable to conceal whole body, with a narrow elevated undulating medial dorsal ridge [image4],some small conical tubercles and a flounced rim. Body translucent white revealing colour of pink  or yellow  viscera . Fine stipple and larger spots of white or yellow-white surface pigment, most concentrated on mantle. At breeding time there may be a bluish area on the right side. Yellowish medial dorsal ridge on rear of body. Robustly built, but has an overall “lacy” appearance.
Apex bluntly rounded. Incomplete lamellae leave anterior face smooth . Translucent white with a few white pigment flecks, densest distally. Mantle area around base slightly recessed, transparent and clear of pigment.
Up to 13 transparent colourless gills in a circle around the anus .
Wide, blunt, flattened oral tentacles , freckled white or yellow-white distally.
Translucent white sole with central area showing pink viscera. Anterior rounded with no propodial extension . Projects behind mantle.
Key identification features
- White “lacy” appearance with some yellowish pigment.
- Reduced mantle with flounced edge does not cover sides of body .
- Ring of transparent colourless gills.
- Some, or much, reddish brown colouring [3Gc].
- Strong medial ridge on oral tentacles.
- Anterior edge of oral tentacle S-shaped [6Gc].
Ecology and behaviour
Rocky shores and sublittoral. Juveniles feed on polyzoans, including Alcyonidium polyoum, Callopora dumerili and Flustrellidra hispida. Adults eat ascidians, including Diplosoma listerianum (EML), Botryllus schlosseri (EML) and Dendrodoa grossularia. Simultaneous hermaphrodite. Spawn laid in spring in curved thick narrow white or rosy belt. Shelled veliger larvae drift as plankton before settling on the sea floor and transforming into adults. Adults die in May after spawning, so inconspicuous until juveniles growing in August .
Distribution and status
South Norway and Faroes to north west Spain. (GBIF map). Common all round Britain and Ireland on hard substrate. (UK interactive distribution map.NBN.)
References and links
Alder, J. & Hancock, A. 1845-1855. A monograph of the British nudibranchiate mollusca. London, Ray Society.
Thompson, T.E. & Brown, G.H. 1984. Biology of opisthobranch molluscs 2. London, Ray Society.
Current taxonomy: World Register of Marine Species (WoRMS)
Irish distribution maps and prey organisms:
Picton, B.E. & Morrow, C.C., 2010. Encyclopedia of Marine Life of Britain and Ireland (EML)