Need help identifying growth on LR

[LarryZ]

A few months ago we discovered this white growth on the underneath of some LR. It is about an inch and a quarter long and half an inch wide. It feels sort of like paper, similar to a wasp nest.

Could it be a feather duster? I bought one that left it's tube after losing it's feathers. I assumed it died. Anyway, I have not a clue.

Oh, and if you do know what it is, should I keep it or is it like a giant sac of aptasia? Thanks everyone!

 

[Ryan Peters]

Might be a sponge, if so they are good filter feeders

 

[captaincaiti]

definitely looks like a sponge. i wouldn't worry about it.

 

[jmf305]

Sure does look like a sponge.

 

[Braves95]

Looks like a sponge. I have some just like it on one of my rocks

 

[LarryZ]

Well it's gone through some changes since I posted this. Any ideas? Doesn't look like a sponge any more but I could be wrong. We're just wondering if some little alien is going pop out of this thing. I apologize for the poor picture quality.

Thanks!

 

[Agostinone]

It does sort of look like an alien cocoon.

Seriously though, how big is it now (can't tell from the pics)? How much bigger is it now than when you first noticed it and how long has it taken it to grow that much (10% in a week, doubled in a couple days...)?

 

[LarryZ]

It grew about a half an inch in the past 10 days. It is about 2 inches long right now. I don't know if grew is the right word as it seems that the "seed" part just stretched the rest of it as it hung from the rock.

I've never seen anything like this but then again I am very new at this. I've had my tank for about 11 months now.