Doris pseudoargus Rapp, 1827. Only red or orange juveniles less than 16 mm long are likely to be mistaken for R. rubra.
1) Much larger than R. rubra, up to 120 mm long, this one 60 mm.
2) Often with large blotches of varied bright colours.
3) No white stripe between rhinophores.
4) Perimeter of mantle not beaded with white caryophyllidia.
5) Variously sized blunt rounded tubercles on mantle; not caryophyllidia.
6) Large tripinnate gills tilt backwards and flare outwards.