Maybe Sponges?

[sushi_and_sashimi]

I recently moved across town and kept an inch of water and wet towels on my rocks for about an hour before I refilled the tank at the new house.

It took me a month to get the sump going again.So the water hasn't been circulating.

I did that last night and noticed these clearish looking critters.

They almost look like tentacles but not centralized to any sort of body.

I have an added livestock in over a year.

Maybe sponges?

 

[sushi_and_sashimi]

More pictures

 

[mmorrison55]

Tunicate I believe

 

[jackintheboxfish]

Yep tunicate. I have those as well. Harmless filter feeders

 

[Subsea]

I concur with tunicates. Excellent bioindicator of a mature ecosystem.