This is a false sea lemon. Not a true sea lemon like in the previous picture.
Divers will tell you that the true sea lemon (nobilis) has the black spots on its back that are between its bumps (tubercles), it has both rhinophores up front and 6 branchial plumes about ¼ inch from the postieror end and both are whiter than the rest of the animal. The guy in the picture is a False Sea Lemon(montereyensis). Note the black dots are on AND in between the tubercles.
Phylum Mollusca, Class Gastropoda, Subclass Opisthobranchia, Order Nudibranchia, Doridacea (this is a sub order that is no longer used but its why many divers also refer to them as Dorids), Family Archidorididae, then the true sea lemon species is nobilis. In the same family they are very similar to archidoris, montereyensis (often called the Monterey Sea Lemon, False Sea Lemon or Monterey Dorid) and odhneri as well as 2 other little yellow guys that are not even that closely related.
