It's a type of nudibranch. With about 2,000 to choose from I just don't have the time yet to match it up. I have a book here with about 500 pages of photos and scientific descriptions to look through as I adore these creatures.
I must state that nudis are not for everyone. They are highly poisonous and without a good skimmer can wipe out a tank. They are also not very reef friendly.
That one is in a holding tank with softie frags to munch on.
If you like them check out, lettuce slugs or this other one.
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