[wildreef]

what color is this "baby anenome" brown you say ?
( i have a feeling its aptaisa ,a nuesence in a reef set up and those things will multiply )
and they can move on their own' ie, detaching their foot and let the water motion move them or by actualy slowly crawling.
So "it most likely" desired to move it's self , not beacuse it fell off the rock by accicdent.

some times feather dusters just dont make it some times and yours may have came out of it protective sheath they make if their disturbed/hassled
( they deisire lite / indirect water flow around them, theyll extend their head of feathers out and filter the water )

feather dusters are "worms" inside that mucus looking tube, and the "feathers" is nothing more than a head in which they grow to catch particulates in the water column ( thats how they feed )

If your water quality is real good you may find the "worm" is lerking some where , and it might attempt to secreet mucus and make another tube for its self to live in.
and yes it will regrow its "feathers" .
look real close in that tank, you may see something ugly and brownish looking worm .
( not to be mistaken for a bristle worm ) in a decent sized feather duster almost resemble a large earth worm ,
thats him naked !lol

but you have a 40 gal. ok so there may not be enough food's for all those feather dusters to take from the water
and some will starve.
( depends on how much you feed your fish )

I dont suggest so many in such a small tank , it would require you to feed to often and make for bad water quality
in the end.
which of course makes it hard on the other inhabitants.