Translucent white thing

At first I was concerned this could be aiptasia, but the aiptasia I had before were more organized in their growth pattern in a ring shape, and the tentacles were tapered to a fine point. This has more of a blunt end to many of the larger tentacles(?). It is whiter than it looks in the photo. It's growing in two spots, the photo is of the larger growth right by my heater. The other growth is actually in the cavity of the lid on the little treasure chest that Finster the clownfish calls his home. Thoughts?

 

Looks like a very cool sponge to me.

 

Following. I have these growng in my fuge. They're not as large as this (just a few "branches"), but I've never figured out what they were. The almost remind me of plant roots and are always on the glass.

 

Agreed!!!

Is there such a thing as a "bad sponge"?

 

It's a sponge.

A bad sponge is one that grows quickly and encrusts over corals...

 

Like a "liver sponge".

 

Thanks for the ID. Now I'm off to read about sponges.

 

Simple filter feeders really. Maintain their steady supply of food, and they'll keep growing. They'll die off if the food supply suffers. Many types won't grow in direct light either (algae typically out-competes them). Also, exposure to air guarantees the death of most any sponge.

 

IME, unfortunately, this is only true for beneficial or decorative sponges. The ones that explode in population and grow over everything don't seem to be phased by air. I have a thread somewhere on here where I was infested some time back. Air, freshwater dip, nothing beat it. Finally had to nuke the impacted rocks :-/

 

That is a very cool sponge, it almost looks like an anemone....