Up to 15mm long (20mm in Mediterranean). When moving, sides almost parallel [image2], giving more rectangular appearance than most dorids. Ample mantle covers whole body, broad margin often extends well beyond foot . Mantle covered with densely packed caryophyllidia ; largest, and most easily seen, are whitish near base of rhinophores , others are translucent coloured as mantle. Mantle bright scarlet , orange , orange-yellow or pink with sparse scattered black  or reddish brown spots  which are often obscured by caryophyllidia. Conspicuous white stripe from rhinophore to rhinophore , sometimes incomplete . Perimeter of mantle beaded with white caryophyllidia . Underside of mantle uniformly coloured as dorsal surface with no markings  & . Genital opening on right, about a third of body length from front.
Slender stem with truncate apex. About 9 large lamellae incline up towards anterior, deeply and widely parted down the posterior and, particularly, the anterior . Translucent white or yellowish white, mottled with opaque white and a few reddish brown spots. Dense large whitish caryophyllidia surround base  .
8 - 11 (11 on 10mm long slug) unipinnate gills rise to form narrow cylinder  from three prone brown arms originating from base of brown erect tubular anus . Translucent whitish with very fine brownish stipple making appearance faintly brownish white.
Often protrudes only slightly beyond foot, digital oral tentacles, visible from underside .
Slightly paler than mantle  & . Translucent yellowish white where it protrudes beyond body at rear when in motion . Anterior edge bilaminate, upper layer slit at centre .
- Rostanga rubra
- Up to 15mm long (20mm in Mediterranean).
- Mantle bright scarlet, orange, orange-yellow or pink with sparse scattered black  or reddish-brown spots .
- Conspicuous white stripe from rhinophore to rhinophore , sometimes incomplete .
- Perimeter of mantle beaded with white spots .
- Mantle covered with densely packed caryophyllidia  & .
- Gills usually held erect to form cylinder around brown tubular anus .
Lower shore, and sublittorally to 60m. Well camouflaged on prey  red encrusting sponges such as Microciona atrasanguinea (SBI), Ophlitaspongia papilla (synonym O.seriata) (SBI) and another Ophlitaspongia sp.. Tubular brown anus ejects line of faeces  which writhes and floats away. If it lodges against the gills, individual plumes act like fingers to push it away. Simultaneous hermaphrodite. Spawn observed June-July.