What on earth is this?

[albie]

What is this critter sitting in front of the sponge? Came as a hitchhiker with Tampa Bay Saltwater live rock.

 

[Rjukan]

@ISpeakForTheSeas

Might need a closer pic and a but of description of what it looks like, moving etc.

 

[ISpeakForTheSeas]

What is this critter sitting in front of the sponge? Came as a hitchhiker with Tampa Bay Saltwater live rock.

That's the hinge (the back) of an Ark Shell (taxonomic family Arcidae) bivalve (bivalves including critters like clams, oysters, scallops, mussels, etc.) - it's a harmless filter-feeder. I would guess an Arca sp., some of which are facultatively mobile as adults (so, the ones that are may move around if they feel like it).

Pics of the top would be useful for a more specific ID, but I haven't learned enough about these to feel confident I'd be able to ID to the species level yet.

 

[albie]

That's the hinge (the back) of an Ark Shell (taxonomic family Arcidae) bivalve (bivalves including critters like clams, oysters, scallops, mussels, etc.) - it's a harmless filter-feeder. I would guess an Arca sp., some of which are facultatively mobile as adults (so, the ones that are may move around if they feel like it).

Pics of the top would be useful for a more specific ID, but I haven't learned enough about these to feel confident I'd be able to ID to the species level yet.

Thank you, that sounds right. It has moved around the tank.