Found a new interesting critter in my sump, what is it?

[Lowlandreef]

I haven't added anything to my tank in months, but I just found this critter attached to a rock in my sump. Very exciting but I'm also very curious what is is. It seems to be calcified (like a vermetid) with a sponge like structure and also looks somewhat like a BTA tip. Does anyone have an idea what this could be?

 

[E.R.A.]

I am gonna say its a type of sponge. I am doing more research. Is it rigid or squishy?

 

[Troylee]

Tunicate sponge

 

[Tired]

Tunicate sponge

Tunicates and sponges are two completely different organisms. They look similar, but aren't closely related at all. In fact, tunicates are chordates, meaning they're closer to us vertebrates than they are to sponges.

There's a simple way to be reasonably sure whether it's a tunicate or a sponge. Gently prod it with something, and see if it retracts. Tunicates will usually shrink up if prodded, sponges don't.

Whatever it is, it's cool. Nice find.