Can I get an ID on this please

[kyle.brown91]

.

My friends in the cycling process of his tank and noticed these little guys on his live rock. Anyone have any idea what they are?

Thanks

 

[cloak]

What exactly are you referring to?

http://www.lionfishlair.com/hitchhiker.shtml

 

[pagojoe]

It's a clam in the Ark family, Acar plicata.