Anyone knows what will "eat" the foot of a clam?

[Aqua Pro Builder]

I recently noticed my friends' clams are slowly missing their feet. The mantle still extend until when the feet are completely rot away, then it will start to decline in health slowly and may eventually die.

What's could have been the problem?

 

[fritz]

http://www.clamsdirect.com/
check the forums

sounds like pyram snails
http://www.reefkeeping.com/issues/2006-09/jf/index.php

 

[Deanos]

All scavengers found in a marine aquarium will eat the foot of a dying clam. An extending mantle, doesn't always mean a healthy clam.

 

[scarf_ace1981]

great question wing. i had this occur twice. no snails that i could see, i think the sand dwelling creatures eat the foot first off a dying clam.