I have this thing in my reef and I can't id it. At first I thought it was a weird bristle worm or something because it has a similar pattern, but its kinda black grey and bright green highlights kinda looks fuzzy like a caterpillar. I went in to scare it once and it turns out that its attached to the rock. when i touch it it sorta pulls in in a vagina shape. I scraped it off the rock once but its come back, and it seems like it might be pissing off my clove polyps. but its hard to say. Sorry I don't have a pic but I'm hoping that someone might get it from the description.
It's very difficult to tell with out a photo, but I would guess a nudibranch. Here is a link (offsite) to a photo gallery of them -http://www.sergeyphoto.com/underwater/nudibranchs.html
It could also be a small sea cucumber, but this is less likely.
what is it
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