Sponge or tunicate

[StickFish]

Im sure many of you have seen this as a hitchhiker on coral rocks.

Its encrusting and slimey, Brown to tan, has a cross-hatching/ reticulated pattern of what looks like some kind of ridge or skeleton inside its tissue, has no visuble polyps or mouths but has sparsed crevaces with riffled white tissue lining it which may indeed be its mouth.

I dont have a big enough specimin to photpgraph but i have seen this animal on many rocks. I could not find it in a large atlas of marine inverts but i am sure one of you can id this life form.

also why is there no forum dedicated to sponges/tunicates

[sunfishh]

I think showing us a picture would help alot