This Nudibranch is one of the most commonly mistaken or mis-identified Nudi’s. Novice photographers who do not bother to really look up the names of their Nudi’s have led to this one commonly being called ‘Goniobranchus Annulatus’, this is a real pain.
So just for reference. The next photo is a Goniobranchus Annulatus, notice the distinctive purple rings around the gills and rhinophores.
Also notice how the title image Nudi does not have these purple lines, that makes them two very dependable and different species of Nudibranch!