what are these?

[hndakd]

I have a bunch of these clam looking things in my tank. I have noticed that they are only on rocks that all came from the same source if that means anything. good? bad? here are some pics

thanks for any help

 

[Mykel Obvious]

can't really tell anything from those pictures... I'd look here for more info on bivalves:

http://www.wetwebmedia.com/bividfaqs.htm

HTH,

 

[hndakd]

Yeah i looked though all that stuff already. I think it could be some kind of spiney oyster. The shells are all in the rock and the mantle is rough. i have yet to physically touch it do to other mishaps with hands. Thanks for the reply