Doris pseudoargus Rapp, 1827.
Only red or orange juveniles less than 16 mm long are likely to be mistaken for R. rubra.
1) Grows much larger than R. rubra, but this juvenile is a similar size; 15 mm long.
2) This one has similar colours to R. rubra.
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.