It’s one of those sea slug that catches one’s attention due to its striking appearance. The background color is a rich pinkish purple with a white border to the mantle. At the edge of the mantle the border is solid white but inside this is a region of varying width in which the white forms a reticulate pattern gradually merging in to the pinkish purple. The rhinophore stalks and the base of the gills is an intense purple, the rhinophore clubs and the gills are orange yellow.
It was mating season I guess, but that was the first time I witnessed this marine critter in such rare intimate moment! Hypselodoris apolegma is its binomial name, a specie of a dorid nudibranch.