ID these please? Some sort of filter feeder or worm?

[RZGreef]

Please help me identify these things? They're starting to show up in shaded areas only that do not receive any direct light. They seem to be out day and night, and are roughly 1/2 cm in length. The rock is just Caribsea dry rock so nothing came on it. The tank has been up about 7 months or so now so whatever they are came with livestock I've added over time. All fish appear healthy, as do corals that I've always dipped in CoralRx before introducing to the tank. I'd love to know what these are, and if they pose any concern. Thanks!

 

[steveschuerger]

I think they might be sponges.

 

[FreshSaltH2o]

Pineapple sponges

 

[Mark Goode]

Pineapple sponges

+1
Harmless filter feeders. My sump's full of them, but they get eaten if they appear in my DT.

 

[RZGreef]

Thank you, everyone! Love this community.