Hitchhiker id - pearl clam like

[Acros]

This hitchhiker looks like a pearl clam when closed. However crawls on the glass like a snail.

It must have come from gulfliverock.

It has 2 symmetrical leafs that closes to give the pearl clam appearance.

 

[vetteguy53081]

I often confused as a clam, it’s a bi valve which is related to the scallop family and generally stationery on rock but capable of moving as you’ve seen
They’re filter feeders and harmless

 

[Acros]

All my other bi valves are fixed on to the rock and this is the only one that moves around. Very cool to see it move around.