Body
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 [5]. Mantle covered with densely packed caryophyllidia [10]; largest, and most easily seen, are whitish near base of rhinophores [3], others are translucent coloured as mantle. Mantle bright scarlet [7], orange [2], orange-yellow or pink with sparse scattered black [7] or reddish brown spots [4] which are often obscured by caryophyllidia. Conspicuous white stripe from rhinophore to rhinophore [8], sometimes incomplete [2]. Perimeter of mantle beaded with white caryophyllidia [9]. Underside of mantle uniformly coloured as dorsal surface with no markings [9] & [5]. Genital opening on right, about a third of body length from front.
Rhinophores
Slender stem with truncate apex. About 9 large lamellae incline up towards anterior, deeply and widely parted down the posterior and, particularly, the anterior [3]. Translucent white or yellowish white, mottled with opaque white and a few reddish brown spots. Dense large whitish caryophyllidia surround base [8] .
Gills
8 - 11 (11 on 10mm long slug) unipinnate gills rise to form narrow cylinder [1] from three prone brown arms originating from base of brown erect tubular anus [4]. Translucent whitish with very fine brownish stipple making appearance faintly brownish white.
Head
Often protrudes only slightly beyond foot, digital oral tentacles, visible from underside [5].
Foot
Slightly paler than mantle [9] & [5]. Translucent yellowish white where it protrudes beyond body at rear when in motion [2]. Anterior edge bilaminate, upper layer slit at centre [5].
- Rostanga rubra
- Up to 15mm long (20mm in Mediterranean).
- Mantle bright scarlet, orange, orange-yellow or pink with sparse scattered black [7] or reddish-brown spots [4].
- Conspicuous white stripe from rhinophore to rhinophore [8], sometimes incomplete [2].
- Perimeter of mantle beaded with white spots [1].
- Mantle covered with densely packed caryophyllidia [10] & [3].
- Gills usually held erect to form cylinder around brown tubular anus [4].
- Archidoris pseudoargus
- Much larger, up to 120mm long, than R. rubra.
- Often with large blotches of bright colours [Ad6].
- Variously sized blunt rounded tubercles [Ad3].
- Anus similar colour to mantle [Ad2].
- Gills tilt backwards and flare outwards [Ad7].
- Head small with vestigial oral tentacles.
Lower shore, and sublittorally to 60m. Well camouflaged on prey [6] 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 [4] 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.
Alder, J. & Hancock, A. 1845-1855. A monograph of the British nudibranchiate mollusca. London, Ray Society.
Anderson, J., Scottish Nudibranchs (ScotNud)
Schmekel, L. & Portmann, A. 1982. Opisthobranchia des Mittelmeeres Nudibranchia und Sacoglossa. Berlin.
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:
Picton, B.E. & Morrow, C.C., 2010. Encyclopedia of Marine Life of Britain and Ireland (EML).
Prey organisms:
Picton, B.E., Morrow, C.C. & van Soest, R.W.B., 2011. Sponges of Britain and Ireland (SBI)