ID this jelly-like crown on the rocks?

[joder2000]

Hola everyone! I hope all is well.

I have a 55-gallon fish only marine tank. The tank is established and has been doing great for the past 3.5 years.

A few weeks ago, I noticed some jelly-like tentacles that have started to grow on one of my rocks. I don't think it's an anemone. I don't think it's a hydra. All I know is that the rock now looks like it's growing a crown.

I've searched the web and can't seem to find anything that will help me identify these mysterious tentacles. I have no idea if they're good or evil...If I should remove them from my tank or not...What the best way of removing them is...What they like to do on Sunday afternoons, etc.

Anyway, attached please find two pictures of these alien-like tentacles. I took these a few weeks ago. More have grown in since they were taken.

Would anyone be able to tell me what type of creature this is, what i could have done to have it suddenly appear in my tank if I haven't introduced any rocks or animals in over a year, if I should get rid of it, and - if so - could you recommend how?

Thanks!!
JR

 

[Fluff]

I'm gonna say sponges but if you have a picture of more advance growth, that would help.

 

[joder2000]

Thanks for your quick reply!

Unfortunately, the tentacles haven't developed into anything, but that jelly-like substance. The rock has more tentacles now, and they're getting longer. But as far as developing more detail or a certain color, it hasn't happened. Well, at least not yet.

The one thing that I can add is that the body of this "thing" has a spiderweb-like look to it.

If they are sponges, should I continue to let them grow?

Thanks.

 

[Fluff]

With the description your giving, I'd still say sponge/poriferan's.

They are harmless. If they grow to nuicense proportions, then you have nutrient issues in the tank. They are filterfeeders so water changes, skimming, watching your feeding etc. will help limit thier growth.

 

[Devilishturtles]

I agree with Fluff. Looks like sponges. I've been seeing some crop up on my liverock recently.

 

[joder2000]

Phew! That's good to hear!

Then I guess I won't remove it since it appears harmless ... and I'll definitely keep an eye on it to make sure it doesn't get carried away.

Thanks for your quick responses.
JR