Is it algae?

[Dirtin]

From the title you get the point. Looks like little zoanthids but are quickly covering my tank. Any ID on them?
https://thumb.ibb.co/djt7RF/20170223_181303.jpg (https://ibb.co/djt7RF)

[Dirtin]

A little more info. Each "polyp" is about a quarter of an inch in diameter. They only grow on rock and it looks like they only spread through contact of affected rocks. That being said, they aren't ugly. I don't want them gone like HA, but if it's the start of something. I saw a post that they might be Acetabularia. But could use some confirmation.

[AlSimmons]

Acetabularia would have been my guess as well.

http://www.saltcorner.com/AquariumLibrary/browsespecies.php?CritterID=2014&filter=0

[BlueCat1949]

Yes Acetabularia! One man's problem algae is another man's dream come true. I had some hitchhike on some seagrass that I brought and really wanted them to grow but they died off in a couple of days.

This is a single celled algae and the nucleus is in the holdfast on the bottom. If you remove the stem and or top part of the algae it can grow a new one.

I would love to have this "problem".

[JZinCO]

blueCat, I've had the same situation. Mine died within days of introduction. From what I have read, a small minority of people find this species a nuisance while the vast majority can't even get a few to hang around long term.