Body (excluding appendages)
Up to 20mm long. Translucent white with orange-red [image 4] to maroon-red  surface pigment on the head, along the flanks below the cerata, on long slender metapodium, and a few streaks dorsally. Colours fade if starved . Slight  or pronounced  white pigment dorsally on pericardium. Dorsal anus to anterior of pericardium. Conspicuous dorso-lateral reddish digestive gland  on each side, branching into each ceras. Distinctive smell, variously described as like Geranium plant or Hydrogen sulphide (bad eggs).
Cerata arranged in indistinct groups of 1-3, the larger ones in each group positioned more dorsally than the small ones . Surface slightly roughened by some small irregularly disposed tubercles. Cerata can be held erect , over the body  or splayed out exposing the body . Transparent, revealing many-branched reddish internal digestive gland extending to the apex which lacks cnidosac. Colour of digestive gland varies with feeding, fades  to buff-yellow if starved. Scattered white pigment spots, concentrate into anterior longitudinal band  on upper half of some cerata.
Enrolled tube, slit down one side . Brownish yellow inside tube. Exterior smooth, orange-brown  to mahogany red , with a few spots of white pigment, except distal end translucent white with numerous white pigment spots. One part of distal end projects finger-like.
Dorsal surface mostly pigmented reddish as body, except large translucent eye patches with “eye-brow”  of white pigment spots. Ventrally, translucent white. Lower rim of mouth is two swollen curved lobes separated by central cleft .
Sole  translucent white showing white spheroids of ovotestis, and internal pinkish red patch near anterior (buccal mass?) visible ventrally  and laterally . No propodial tentacles, but anterior indented at mid point and expanded slightly laterally, so appearing bilobed . Can extend far to posterior of cerata; then total length of animal about 20 times width of foot. Dorsal rim of foot white .
- Body translucent whitish with dendritic green markings.
- Rhinophore enrolled, widely slit open down anterior, with dendritic green markings.
- Length about 8X foot width when fully extended.
Shallow sublittoral where enough light for foodplants: red algae such as Griffithsia (Algaebase) , Delessaria (Algaebase) and Heterosiphonia (EML). Rarely at ELWS, but can be found within arm’s reach on constantly submerged fine red algae on floating pontoons. Very well camouflaged on red weed. Simultaneous hermaphrodite. Small spawn mass contains 550 or fewer ova, with diameter 0.005mm, smallest recorded ova for a British opisthobranch. Spawn reported in July, September and October. Shelled veligers drift as plankton before transforming into adults.
Shetland to Portugal and Mediterranean coast of France (GBIF map). Scattered records in Ireland and west and south coasts of Britain, but probably under recorded; suggested search method to take samples of fine red weed from pontoons etc for examination in water under magnification (UK interactive distribution map).