Shell Fish?

[lewiss]

I think I have some mini shell fish in my tank?! I found a clump of about 6. About 1inch long, and green / blue. I think they might be mussells?? They're that Kim of shape. I haven't bought them or seen them before.
Any ideas? Can mussells Hitchike?

 

[sorgan]

Yes bi-valves are a common hitchiker.