Is this a muscle?

[lukefish]

Just brought home a nice zoas and noticed a small, black shell on the side of the rock. I’m pretty sure it opened and closed but maybe it was the refraction of the glass and water playing tricks with my eyes.
Is this a common hitchhiker if it is indeed a muscle? If not, what is it?
I’ve had a look at the list of common hitchhikers and I don’t see it on there.
As you can see it looks flat at the top and has an opening running down the centre... like a clam.

Very muscle shaped I’d say!

 

[MnFish1]

Looks like without a better view, its hard to tell... But - it kind of looks like one.

 

[lukefish]

Ok it’s 100% opened!!!

not sure you can see it in the pic

 

[fishguy242]

hi,yep ,bonus filtration..

 

[lukefish]

Just when I thought this hobby couldn’t get any cooler!!! I now have a pet muscle!!!!

 

[Paul B]

Is this a muscle?​

No, But it probably is a mussel.

Mussels have muscles to close their mussel shell but that is a mussel.

 

[MnFish1]

Ok it’s 100% opened!!!

not sure you can see it in the pic

I don't see it - but I think I know what you mean. How open is 'open' (ie. the distance between the top and bottom 'shell'. The reason I ask - is that at least the way I see that picture - if its 'open' its more wide open that I would expect (i.e. possibly not healthy) - but again - its hard to seem.

 

[lukefish]

Is this a muscle?​

No, But it probably is a mussel.

Mussels have muscles to close their muscle shell but that is a mussel.

Hahaha. Well I feel like a right plonker!!! Very well played

 

[jft]

Is this a muscle?​

No, But it probably is a mussel.

Mussels have muscles to close their mussel shell but that is a mussel.

HAHA MY thinking EXACTLY!!!

 

[lukefish]

In addition to the muscle/mussel I’ve just spotted this.... no clue what it is. It wasn’t there yesterday. Looks like a shell

I can’t get a better pictures than these

Any ideas as to what it can be?

 

[lukefish]

In addition to the muscle/mussel I’ve just spotted this.... no clue what it is. It wasn’t there yesterday. Looks like a shell

I can’t get a better pictures than these

Any ideas as to what it can be?

It looks like a green and red stripe with a slightly spiky surface... if that helps by way of description