Mystery starfish. And others.

[mikebusc]

So I know this is some sort of starfish, but I have no idea where it came from! Just noticed it on my tank glass now. Could something have been brought in from a recent addition to my tank? Or an addition a long time ago rather?
And also, while I’m, at it a couple of other things growing under my Feather duster. I’ll show some pics from a distance and then closer up. Hopefully it comes out OK.

 

[Cincyreefer513]

Asterina starfish and aiptasia. Both are unwelcome guests.

 

[formallydehyde]

Before you freak out, *most* asterina starfish are harmless and potentially beneficial. They're small, quite hardy and usually avoid bright light so it's common for them to hitchhike in and go unnoticed for a while, especially if you don't view your tank at night a lot. They probably hitched a ride hiding on a pore in the live rock (assuming it's live) but they're also not unheard of on coral frags and such.

The red circled things as cincyreefer pointed out are aiptasia anemones. They can multiply easily and sting corals if they attach close to them, so they're generally viewed as a pest. If possible I would just remove the one in the sand by scooping the whole anemone and the sand its attached to out. The one on the rock is trickier because it's so close to the feather duster, but you might be able to just get rid of it by scaring the duster into retracting and using coral glue with a narrow applicator (or syringe) and entombing it in a little dome of glue. Make sure to keep other animals away from the glue until it solidifies.

Or you could just keep an eye on the one on the rock and not do anything about it unless it becomes an issue. Aiptasia can respond to injuries by multiplying so sometimes getting overly aggressive with them can do more harm than good.

 

[mikebusc]

I appreciate the replies.
I thought maybe the feather duster was multiplying because they had the same white markings on them

 

[mikebusc]

So I scooped out the aiptasia that was on the sand and encased the small one in BRS "super glue" which was in the crevice of a rock so it was very easy to do. I'll keep looking for more as time goes by.