strange clam type hitchhiker

[lotekfish]

I recently noticed this white thing growing on a rock full of zoanthids I bought from Divers Den a few months ago:

https://c1.staticflickr.com/5/4638/25693758028_25bcdb4ed2_b.jpg

It's that white disc with dots that's about the size of a paly head. I first I thought it was some sort of sponge but when I got near it with a wood stick it contracted like a clam. You can kind of see from this photo a black edge around the outside:

https://c1.staticflickr.com/5/4682/25693761148_eeba54da28_b.jpg

When the top contracts that black edge disappears. I did end up touching it with the wood stick and that white surface is hard. Any ideas?

 

[lotekfish]

Sorry images don't show up, I can never seem to find the URL in Flicker- I used photobucket for too long... now I'm old and can't learn new tricks

 

[Gareth elliott]

I cant really see it to get a great look, maybe an Abalone?

 

[lotekfish]

Wish I had a macro lens, that's as close up as I can get, but I think you're right- looks a lot like an Abalone!

 

[Tahoe61]

Are you sure it's not a tunicate?
Is it always in the same location?

 

[lotekfish]

It has not moved since I first noticed it a few days ago, which probably rules out the abalone. Would a tunicate show movement? It is an odd thing- it has a dark colored fleshy part a few millimeters in thickness that is attached directly to the rock where is sits in a slight depression, and it has a shell on top. So in form it is a bit like a abalone except it doesn't seem to move around. If you pass something slowly over it a few inches away, it will close the shell down tight to the rock- so has some sort of photo receptors. The shape of the shell has grown to the contour of the rock so it fits the depression exactly when closed. I don't know if it was always there but I only noticed it a few days ago. It's possible the shell part was a darker color that matched the rock so i didn't see it- and maybe some new growth or a snail cleaning made it white.

I'll keep an eye on it and maybe try to get better photos if it grows.

 

[Livinlocal]

Hmm this is hard to tell from the pictures but the description sounds like a very small clam or a tunicate. Maybe google them if you’ve never seen small ones and report back if they look similar

 

[Livinlocal]

Or some sort of mussel