hitchhiker1

Looks like a whelk, not sure though. I'd get it out if it is ASAP. They will eat clams and they are not very good to have in a reef.

I think it is probably a Nassarius. Seems to move quite quickly. I am not planning on keeping any clams anytime soon I will wait for him to get a bit bigger to get a positive identification.

http://www.melevsreef.com/id/whats_a_whelk.html

I have a bunch of these in my tank. Bought them from IPSF. They're sold as strombus snails but Ron Shimek says they're probably something else: columbellid snails (Euplica or Pyrene species). They eat algae in my tank and do lay a lot of eggs - got little baby snails all over! They don't get very big though, maybe about 1/2" max. They're cool. Enjoy.