found !! but not wanted

[Trippy]

Hey there...was wondering if someone could help me classify what i have in my tank...they are mostly in dark places...kind of round in shape...and have a tuft in the center of them...light in color almost white...and i touched one of them and the tuft came off like a hat and left the mass there with a hole in the top of it...it came off rather easy.
they are kind of invading ...anything i can do...? and what the heck are they?

Thanks
Trippy 8O

 

[Chucker]

Sounds like a small sponge, common in young systems. Pics are in the HHFAQ.

 

[nilestr]

Do they branch out looking kind of like a oak tree without its leaves?

If so then it is a sponge. They seem to get about a inch off the rocks and inch in diameter.