This is Hopkin's rose (Okenia rosacea) a dorid nudibranch. Even though it possesses tall papillae like the aeolid nudibranchs, you can see that it does have an external gill plume, which places it firmly with the dorids.
These nudibranchs lack oral tentacles, but do possess rhinophores, which you can just see sticking up out of it's head. They also have an interesting smooth hook on their radular teeth which lead them to have their own genus for a while. However, recent phylogenetic work using several morphological characteristics, shows them to be a monophyletic group within the Okenia genus (Gosliner, 2004).
They feed upon a bright pink bryozoan, Integripelta bilabiata, which is where O. rosacea gets its rosy color from.