What are these things?

[kay-bee19]

The rock with button polyps I purchased not too long ago apparently came with some "hitchhiker" polyps of some type. They're reddish-brown, and are comprised of a stalk and tentacles or arms (which have bristles or rudimentary feathering on them). They're really tiny (less than 5mm so far). I don't think they are aiptasia, but I have no idea what they are.

Due to their size, my camera had difficulties adequately capturing them. Here are some poor-resolution pics of them growing among the button polyps:





Tonight I noticed reddish-brown 'algae' growing on the side of this same rock, but upon closer inspection it's actually a mass of these extremely tiny organisms (a tiny fraction of the size of the ones in the above pics):



Any idea what they are? (I think they're some type of polyp which is why I posted here). If these are some type of aiptasia, I'm in trouble! (this growing mass must have sprouted within the last day or so, I just discovered it tonight)

[Rockitmakr]

My guess is that the polyps are brown button polyps that have been disturbed so they are not out like the others, not aptasia. The brown stuff on the side of the rock looks like diatoms.

[kay-bee19]

They look totally different from the buttom polyps (sorry I didn't mean to suggest the closed polyp was the organism I'm inquiring about, I guess I circled both the close button polyps and the smaller unidentified things adjacent to them).

Here's two of the organisms (hopefully with clearer annotations):



The red-brown mass is comprised of exact copies of this organism except considerably smaller, which leads me to believe they will eventually grow in size. My camera had difficult capturing them, but perhaps in the 3rd pic I posted you can see their outline at the very bottom against the shadows.

[FLricordia]

Think they might be some sort of fan worm? Do they retract when touched?

[TypeR632]

tag

[SitBackAndWatch]

I have the same things in my tank.

they retract ever so slightly, i had on fall off a rock last night when moving it around. It floated away into one of my power heads and got chopped up, my coral banded shrimp seemed to have liked the pieces of it...

[zoomfish1]

Could be small marjano anemones. If so they are slow growers but spread quickly. They are considered nuisances.