Tiny clams

[hunterdaddy]

I have been finding little tiny clam shells on my sand. They are about double the size of a pencil erase but smaller than a dime. I see a few live ones also but they probably wont stay alive long as something is eating them.
Any idea what they are??
55 gal
whisper filters
4 inch dsb
30 lbs lr
1 powerhead
5 blue leg hermits
1 green crab
1 green chromis
1 gold bannded maroon clown
1 fire shrimp that wont leave his corner EVER
1 skunk cleaner
1 astrea snail

 

[nss11110]

there is a sand sifting clam ( ive seen them advetised) but dont know the name of them. seems like it could be them. there is probably someone eating them in your tank at night or it could be just after they die they are eaten