ID Please
 

I found this guy in my tank. It's a new tank but I bought live sand. Any ideas? I've found 3 without really searching too hard so I am assuming there are lots of them.

Flatworms
Not a good thing to have.

I can't say its for sure it's a flat worm? Doesn't really look like any I've seen, here are a few pics for you to compare: http://www.melevsreef.com/critters/flatworms

If they are stuck on the glass and slithering about, then I would agree with Coasting. Probably some species of flatworms. There are a lot of flatworms out there!

Disagree. There are many species of flatworm that are beneficial. The bad ones tend to be a different shape and color with less of a fork tale. Dark brown or red ones are the worst. If they are the bad ones they multiply by the hundreds in days. Ive had them, and they are terrible. Ones that are clearer and elongated with fork tales are generally ok. If you're worried, a six line wrasse can keep populations in check. I wouldnt worry about those ones.

I agree, not something I'd worry about. I've found similar things over the years, they always tend to simply vanish.

I thought it might have been a flatworm but then noticed it was not flat at all. This one is fat, like a slug, with a fork tail. Is fork tail a flatworm only characteristic though? And when you say "different shape" does that included, not fat?

Could even be a nudibranch. But unless its eating something like corals, or multiplying like crazy I wouldn't worry about it

Yesterday I found 3 and this morning I see 8, all in the same area of the tank so I don't know if that's multiplying too fast. This tank is going to house Seahorses and Pipefish along with some frags from my other tanks (mostly mushrooms and polyps.) I tried to kill the ones I found this morning but they don't squish like the other flatworms I've had. They're too fast and too little, I guess I will just monitor them and see what happens.

Thanks for the help!