Up to 60mm long. Ample mantle covers whole body. Sandy-brown [image1], grey-cream, yellow, buff-orange, white (Flickr) or bluish white (Flickr), often with faint freckles like those on a fair skinned human, and often a few dark marks in two or three longitudinal rows. Mantle densely covered with tiny tubercles, barely visible to naked eye; under magnification, each has coronet of spicules around retractile papilla. General appearance velvety; soft and yielding to touch. In profile, anterior often stepped lower than rest of body . Mantle slightly raised into rim around rhinophore base and into a pronounced collar around gill pocket .
Short and stout, base pale, distally ten to fifteen close set lamellae, and a short nipple like apex. Smooth base often more swollen than lamellate section . Lamellae often with dark brown speckling near apex. Rhinophores stand in distinct pits.
On adults, 15, sometimes 17, large, pale tripinnate gills around contrasting dark brown anus . Basally surrounded by raised collar .
Mouth can project into short tube . Thin oral tentacles only visible from underside.
Sole white or yellowish, split into two layers at anterior; upper layer projects forwards and has cleft at middle . Protrudes at posterior when in motion .
- Up to 60mm long, similar size to many Archidoris pseudoargus.
- Sandy , buff, whitish (Flickr) or bluish white (Flickr), any other marks small and dark.
- Very small tubercles; velvety appearance, soft feel.
- Large pale gills around dark brown anus .
- Base of extended gills surrounded by raised collar .
- Up to 120mm long, half grown ones similar size to Jorunna tomentosa.
- Mantle usually yellow or buff-orange, often with large blotches of bright colours [3Ap].
- Variously sized spiculose tubercles give stiff unyielding feel to mantle.
- Gills often blotched with colour.
- Gills tilt backwards, not upwards from a raised collar.
- Underside of mantle lacks dark markings (may have slight staining at edge) [4Ap].
- Head small with vestigal oral tentacles.
On lower shore and sublittoral fringe. Well camouflaged on prey; Halichondria panicea (EML) and Haliclona spp. ( EML & EML) Simultaneous hermaphrodite. Spawn, February – August in Britain, a spiral ribbon attached by its edge in a tight coil to substrate or food (EML). Planktonic veliger larvae for about three weeks before transforming into adult form.