Can any one help me ID please

[dellboy1986]

Can any one ID please
Dose any one know what it is growing on the side of my hammer coral over had this coral for about 6 months and I only noticed it about 2 months ago I was thought the coral was growing as this was my first go at keeping hard corals but tonight I was looking at it and it reacts to light and movement is this a good thing or bad

 

[cvysochin]

Its a type of clam. To which type I'm not sure of. But it's most likely harmless. Also no need to do anything special as far as care. These hitch-hiker clams are hardy little buggers. :)

 

[TrialandError]

It's just a filter feeder. I forget what they are called but I had 2 of them down to 1 now :(