Introducing Bit-o-critter!

Here's the first in a new series of posts.  I have taken an abstract crop from a photo of a marine animal, and I want you to tell me in as much detail as possible what. it. is.  First correct answer in the comments wins; you get extra points for species level ID, and extra extra points for telling us something we didn't know about said critter.  The prize?  My undying respect and affection, and a tremendous sense of smug self-satisfaction on the bus on the way home.  Maybe at some point I'll actually pony up something decent for you, but lets see if you can get any right first...

Here we go.  Easy one to start: