Looks like a sponge but moves

I have had this on a rock with some star polyps thought it was a sponges but it started moving. Any ideas?

 

maybe a chiton?
a snail?
um.. this is pretty much a guessing game without pics

 

Need a pic to ID

 

Pictures

Sorry did not post with original message

 

Don't have the foggiest idea but it is cool. I think it is safe.

 

It really does look like a sponge. But I haven't a clue to what it is either. Sorry

 

sponge bob squarepants?

 

but he isnt squared.. Must be grandma sponge..
if what im looking at its the little round thing with the little tail looking thing.. ( resembles a horse shoe crab)
not sure really.. never seem anything like that..

can you grab it and look at it.. and then give us some details of the general body shape underneath and all.

 

Is that a little cyno on the rock the string or tail is attached to?

If so this might sound far out but it could just be a blos of cyno???

 

thats what i thought too actually..
sometimes cyano somehow traps a bouble.. ( im guessing its Co2? right?) not sure really.. but that could be it too..
try touching it and see if it bursts.