Weird goo on rocks

[Miami Reef]

I don’t know what these are, but there’s at least 4-5 of them around the tank, attached to the rocks.

 

[Rjukan]

Looks like a type of sponge to me. Harmless and a indicator of a healthy system.

 

[vetteguy53081]

Sponge yes and harmless and can be ornamental.