ID Please

[ScubaSteve]

Looks like a sponge. Harmless and beneficial. I have the same kind of sponge in my tank (is it kind of purple and there might be a large opening in the middle of the bulk on the rock?). To my understanding it has not been described by science so there is no scientific name I could give you for more info.

[xnmuller]

Thanks for the information, I was a little worried it was a nuisance and would take over or something.