Peculiar Live Rock Hitchhiker - Sponge? Something Else?

[jmcdona6]

Tough picture I know but here is what I have. Rock is from TBS so likely some sort of Gulf hitchhiker. Its pure white - sort of like a jumbled mess of styrofoam or dense cotton, looks almost like a sponge...but it moves. One day it might be on one side of the rock...next the other. You can't see it moving but it does. It reacts (contracts/contorts) to snails and crabs if they touch it...it picks up things like its sticky and has encrusted itself with substrate before almost like a feather duster does.

It has no normal biological features really at all, except for little tentacles at night...but I think that might be a spaghetti worm that is in or around it. Maybe its a free floating sponge and that what is causing it to move/react?

Doesn't seem to be harming anything. Stays on this rock. Just peculiar...never seen anything like it.

 

[BryanM]

Pic is pretty blurry, not sure what that could be.

 

[jmcdona6]

Pic is pretty blurry, not sure what that could be.

Yeah it is, middle of a large tank, hard to get a good pick on a phone. Maybe I can get my wife's real camera out at some point. Or move the rock closer to the glass next time I am cleaning.

Not sure it would help though. Its literally just a piece of white fluff stuck to the rock. Doesn't really have any texture or features. Almost have to think its some sort of sponge considering that fact. I just haven't seen a sponge that moves...not without the help of something else. Kind of leaning toward a sponge being hosted by some sort of other critter...like the spaghetti worm I spoke of. But its odd behavior for them and I wouldn't think them strong enough to transport another object around.

 

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Tough picture I know but here is what I have. Rock is from TBS so likely some sort of Gulf hitchhiker. Its pure white - sort of like a jumbled mess of styrofoam or dense cotton, looks almost like a sponge...but it moves. One day it might be on one side of the rock...next the other. You can't see it moving but it does. It reacts (contracts/contorts) to snails and crabs if they touch it...it picks up things like its sticky and has encrusted itself with substrate before almost like a feather duster does.

It has no normal biological features really at all, except for little tentacles at night...but I think that might be a spaghetti worm that is in or around it. Maybe its a free floating sponge and that what is causing it to move/react?

Doesn't seem to be harming anything. Stays on this rock. Just peculiar...never seen anything like it.

Could it be a decorator crab?

 

[jmcdona6]

Could it be a decorator crab?

I had one of those too...now in the sump after it favored a kenyan tree.

But no...no crab that I can see. Just a wad of white fluff.

 

[jmcdona6]

Could it be a decorator crab?

I have a hypothesis.

Hard to photo but if I look closely there is a small tube built up on the side of the rock made out of shells and other substrate. I noticed it after I briefly saw an odd looking worm hanging out of it during feeding time. Only time I have ever seen it and hasn't come out since. Doing some googling, it looked most similar to something of the species Diopatra Cuprea (Plumed or Decorator Worm).

I had noticed some odd shell formations on the rock before but it all got bulldozed by one of my conchs, didn't think much of it. Shortly after the aforementioned white disorganized wad appeared. I wonder if it isn't some excess or orphaned Mucous polysaccharide that the worm uses to build its tube. None of my research indicates a color, but it would explain why it readily sticks to the rock. The perceived movement being it getting pushed and pulled around the rock by the flow, snails, etc.

Only thing that makes me doubt that hypothesis is its remarkable ability to stay clean. If its sticky enough to stay on the rock, attaching, detaching, and reattaching, it should also be stick enough to attract bits of debris that may come into contact with it as well.