What in the world is this?

[Emery]

Some kind of sponge? There's two that I found so far, both on the underside of a rock (no direct light).

 

[cloak]

It looks like a sponge to me as well.

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[Macdaddynick1]

Yup it's a sponge it's really sticky and slimy when you touch it unlike other sponges that usually feel like cardboard. And it can take over the corals too