White cocoon white antennas what is it?

[amigo003]

I got a tank from a fellow hobbyist. He was leaving and couldn’t keep his tank. After a couple months I started seeing these white cocoons sticking up off the rocks. I have no idea what they are. Does anyone know?

It’s fascinating what grows in salt water…. Almost scary what’s in there.

Are these a type of sponge?

 

[ISpeakForTheSeas]

They are a type of sponge, yes - pineapple sponges (genus Sycon) to be precise. Harmless filter feeders and very common in newer tanks. They usually have a population boom then bust, eventually going away on their own after a while.

 

[MoshJosh]

Pineapple sponge. Harmless filter feeder.