What is this ? please ID, good or bad?

[duromega]

Hello fellow reefers
I saw this yesterday and didn't pay too much attention and today I have 3
I'm kinda worry because I have no clue what this is

when the hermit crab approaches it closes like a feather duster

here is closed:

is this aiptasia ?

 

[m'akoyPINOY]

you're right,it's a feather duster.

 

[rookie07]

you're right,it's a feather duster.

+1

 

[duromega]

how did this end up here ???
my rock was dried for 3 days after that rinsed with freshwater, brushed, cured for a few weeks, how is this possible ?

 

[lfsmarineguy]

Life finds a way.

 

[thirty6]

I have a couple too on my rocks. Exactly the same

 

[House of Laughter]

Life finds a way.

+1 - in very weird ways

House

 

[arnaldolex]

i have prob hundreds its ok

 

[cmantis]

Yup freaked me out at first when I realized I had them but all good now that I know what it is.

 

[duromega]

wow this hobby is fascinating!

 

[reefer4eva]

wow this hobby is fascinating!

The many different creatures at night under moon lights always fascinated me

 

[SteveZ15]

I have tons of them too,snails all sorts of stuff pop up..its cool when they spawn it looks like smoke coming from the rocks.