Friend or Foe?

[oldbob50]

This little guy showed up last night on my Zoa rock. A few stationary clam like critters came with the Zoa rock, are imbedded among the Zoas and open at night to feed. However, this thing just showed up and moves under it's own power. I know it is a bivalve mollusk but what type and is it a problem for a reef tank? It has a more elongated shape than the imbedded mollusks and is about 3/4 of an inch in length.

 

[aKlevans]

Looks like some sort of bivalve. I haven't heard of any bivalves that have been pests whatsoever, so I say its a good guy.

 

[ThunderGoose]

Got any pictures from the side?

Uncommon hitchhikers can be hard. There are thousands of possibilities. Was this zoa rock from the ocean? If so, where?