I’m not sure how common this tiny tiny nudibranch is, but I do know it fits extremely well into its surroundings.  This little one was found at low tide while I was kayaking on some flattened eelgrass beds.  It was no more than 10mm and barely visible to the naked eye — they blend in so well with the bryzoans on which they feed.  My camera caught it before I did.    Here’s an interesting tidbit:  Palio zosterae copulates by hypodermic injection — for more information on how this species is able to use its penis as a hook to pierce the skin of its mate, check out the Sea Slug Forum’s description.