Tiny White Clams

[thecoralbeauty]

I received three of these tiny white "clams" as a gift from someone, claiming that they are clams. I sort of think they might not be clams, but, i really can't tell. Can anyone tell me if this is actually a clam or something? They don't seem to be bi-valves, anyway.

 

My urchin is wearing two of them here:

 

[ndrobey]

Definitely limpets. They are in the gastropod family and eat algae.

[amphipod]

Can you get a clearer shot please, maybe less light will help.