What is this

[meco65]

Could it be a sponge?

[Nykademus]

Looks like a pineapple sponge. A good filter feeder and an indication of good water quality.

[Sk8r]

Yep. They'll grow happily at a certain stage of your tank. Then go away.

[meco65]

I thought this was a pineapple sponge.

[aquatics junkie]

looks like what the people above described. I remember getting some of this in on live rock and such.

[meco65]

Thanks all

[blakemiller1981]

def a sponge of some type ill go with pineapple like everyone else lol

[gwainrig]

Good ID. Do you have any others?

[Chiefsurfer]

doesn't look like a sponge to me. It looks like a "shelled" critter, like a snail or something. I believe I have 2 of these same things, and they do not seem to move, but seriously looks like a snail, or shelled critter of some kind.