What is this?

[bkneeland]

There are several of them in the tank, and this is the largest. It's approx. 2 inches long & 1/2 inch wide. The slit down the center opens and closes from day to day. It seems to be very slow growing whatever it is.
Does anyone have any idea what this is?

 

[jimmy 4]

I have those as well. Mine are kind of grey though. Im not sure but i think that they are a type of sponge.

 

[bkneeland]

Maybe a sponge....never thought about that, wish i could get a better picture

 

[reefkprz]

I would say sponge as well. there are about 5000 different sponges so there is a pretty good chance it is one. I like the orange rust color. I have several types in my tank, yellow, purple, and black sponge, I had white ones too but they seem to have passed on.