Sponge or?

[Raamiah]

So I recently got a CUC from Reefcleaners and today I noticed this on one of my snails. Is it a sponge or what might it be?
To me it doesn't look like corraline because it's not flat. Not sure how else to describe it but I am almost 100% sure it's not corraline algae.

 

[kevnkev]

Here's my favorite way to id it as sponge vs. something else: touch it!

Does it have some squish and give to it but still feels rough? Probably a sponge. Encrusting sponges are hard to tell because they're so thin, but you can still feel that soft-but-rough.

 

[Raamiah]

Now I gotta find the snail tomorrow when I get into work and poke it. Fun.

 

[Raamiah]

It def had some squish to it but it felt more smooth than rough. It's really small so it's hard to tell.

 

[SaltwaterNoobs]

Looks like a purple sponge I've seen in my LFS's main tank. They've actually fragged it off and sold it several times because it not only grows well, but it is a really "pretty" sponge, too It is smooth and soft to the touch, so not as rough as most sponges, and it is a dark purple/grey color. I'll try to get a pic of it next time I'm in, but it will be a while. I'm 99% sure it is what you have there on your snail, though. Is the type of snail it's on nocturnal?

 

[Raamiah]

I actually discovered today that the shell has been taken over by a crab. Or maybe it was a crab the whole time and they thought it was a snail when they shipped it to me.

Anyway it's on a crab not a snail.