Revised July 2012
Body Up to 14mm long. Ample mantle covers whole body [image 9]. Usually white or yellowish white, but can be yellow, especially in northern Scotland. Surface between tubercles can appear frosted if fine embedded spicula  catch light. Usually no surface pigment, only rarely has brown freckles. Club-shape tubercles with flat  or broad rounded  tops on mantle. Only the very smallest tubercles on the mantle edge sometimes have pointed tops.
Apex truncated. Up to 12 front-parted oblique lamellae on 14mm long animal. About 10 lamellae  on 8mm specimens. Translucent white, often slightly tinted yellow, or, on yellow specimens, darker yellow than mantle. Usually no surface pigment.
Up to 11 rather short transparent gills, coloured as mantle, in a circle, broken at rear, around the anus. The posterior gills barely showing above tubercles .
Large oral veil .
Sole with sparse spicules, coloured as mantle, translucent, showing tapered brown digestive gland and adjacent white  or yellow  ovotestis. Anterior of foot gently rounded, not indented by mouth . Usually completely concealed dorsally by mantle, but posterior tip may sometimes protrude.
Key identification features
- Club-shape tubercles on mantle, flat  or broadly rounded  tops, only smallest at mantle edge are pointed.
- Maximum size in wild usually 14 mm.
- Usual maximum of lamellae on rhinophore is 12.
- Usually white or yellowish white in S. Britain, yellow in far north, but can vary.
- Club-shape and torpedo-shape tubercles on mantle have narrow rounded point [7 & 8].
- Maximum length usually 17mm.
- Usual maximum of lamellae on rhinophore is 19.
- Usually yellow in southern Britain, whitish in far north, but can vary.
Ecology and behaviour
On lower shore and sublittorally to about 200m. Feeds on wide variety of polyzoans, including Electra pilosa (EML) (often on Fucus serratus), Membranipora membranacea (EML) (often on Laminaria) and Securiflustra securifrons (EML) (sublittoral). Simultaneous hermaphrodite. White spiral ribbon of spawn laid January to May in N. Wales. Adults die after spawning so inconspuous until next generation grows. Further north, breeding is later. Planktonic veliger larvae before transforming into adult form.
Distribution and status
Iceland and Spitzbergen to Atlantic coast of France and eastern USA. Also records from Pacific coast of America. (GBIF map). Common and widespread round Britain and Ireland on hard substrate, most records in North.
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 map and prey organisms:
Picton, B.E. & Morrow, C.C., 2010. Encyclopedia of Marine Life of Britain and Ireland (EML)