A mating pair of Nudibranch - Tyrannodoris luteolineata. Although Nudibranch are hermaphrodite, they still needs to mate to reproduce and in some instances, they 'fight' to determine which among them will be the male or female. The winner is the 'male' as after mating, it can moves on whereas the losing 'female' will have to find more food to produce eggs.
Personal milestone, species #4000
"Tyrannodoris luteolineata" is a species of sea slug, a polycerid nudibranch, a marine gastropod mollusc in the family Polyceridae.