Can anyone help me ID this thing?

[ladydave]

I found this moving across my live rock this morning.... Fished it out and it retreated into its shell. I don't know where to post this, no idea if it's a snail or bivalve. All I want to know is should I get rid of it?

 

[Tahoe61]

It's a bi-valve of some sort, harmless. What you saw was the foot.

 

[ladydave]

Thanks so much for the reply! Are you sure??? It seemed to be moving very fast across the rock for a bi-valve!

 

[Tahoe61]

Yes I am pretty sure. Two shells joined by a hinge at the bottom? It shuts entirely when disturbed or moved?

 

[ladydave]

Thanks! You're right! I didn't see it open much at all and just saw it scooting across the rocks.... Really quite quickly which is why I thought it was a snail. I only noticed the 'hinge' when I took that picture and zoomed in, I was convinced it was some evil Zoa eating snail till then!

It's back in the tank now.... Moved about 8inches in 15minutes which is faster than some of my snails!! Can't see it today so assuming it's found a nice place to call home!

Thanks for the response.