Live Rock - What are these and what happened to them?

[flyingscampi]

When I bought live rock for my new nano it was bare except for some coralline.

Then loads of 'things' sprouted out of it (two examples arrowed in picture) and they looked really nice. Then they all disappeared and I ended up with bare rock again. I did notice an asterina starfish munching on one of them so I presume that they all got eaten.

So can anyone tell me what they are, what is likely to have happened to them, and whether there is any way of re-introducing them?

Population wise, I only have a small hermit, a trochus snail, 2 x sexy shrimp, some asterina starfish, and lots of pods. I know the asterina are classed as a pest but they feast on algae and my enemy's enemy is my friend..

 

[Tamberav]

Mermaid's Cup macro algae (Acetabularia crenulata)

From reef cleaners:

Each sprout of Acetabularia crenulata is actually one cell, (one of the largest cells in nature), the part that matters is the part attach to the rock itself, and while that part is microscopic, if only it survives, the entire plant will do just fine. (The caps don't even matter really). Just give it some time and TLC and it will bounce back.

 

[X-37B]

Asterinas only eat coralline algae in both my systems.
I dont have any other algae for them to eat.
I would remove it unless you want hundreds of them down the road.
Your pics could be a feather duster or some type of clove polyp.

 

[DrZoidburg]

Would agree its one of the acetabularia species. There is a few different kinds.

 

[flyingscampi]

Acetabularia - that's the ticket! Thanks for letting me know.

I guess I could try turning the rock over and see if anything pops out.

The asterinas definitely eat algae as I watched one clear a section of rock. My tank is only 15 gallons so I can hopefully remove them easily enough if they get out of hand.