Any ideas what these things are?

One way to tell if they are sponges or not is to take them out of the tank for a minute, then put them back. If they live, they are not sponges. Sponges cannot be exposed to air.

 

If they are a type of featherduster worm or a type of anemone, wouldn't that be true too?

 

David Renke and his quick eye noticed that my Unknown Tiny Creatures are the same as the ones discussed in a thread from RHorton from last week (17 Sept).
The answer given in that thread was that they are a type of sponge.

 

that reminds me of the old way one would tell a witch from a non witch.
Personally i don't think one should recommend such a cruel method for determining if an animal is one kind or another.

Google is your ally, and it won't cost lives.

 

LMAO

 

I think they are little sponges.

 

pineapple sponges also called urn sponges.harmless and will help filter your water.they can grow anywhere including inside your filter boxes.

 

quick question...how things like these come out of nowhere?

 

That's a good question. I think they were always there, but the tank wasn't healthy enough for them to grow and multiply.
In my case, I've had algae problems off and on for 2 years. The green hair algae and red slime algae finally went away and coraline is now all over the place. A sign of a healthy tank, and the sponges have responded to the improved conditions.
I found a really large bristleworm in my tank last month. He's probably been in the tank for months (if not years) but I never saw him.

 

not all sponges die when exposed to air.