featherduster and sponge. maybe?

[KodiakBear]

I've been searching through all the ID threads and links to no avail. Anyone have any idea what kind of filterfeeder this is?

another blurrier view:

It does not have a leathery tube like the other featherdusters in my tank. It comes right out of a hole in the LR and disappears completely back into it when disturbed.

I have a growing number of these in my tank:

I think they are some sort of sponge, but really not sure. They only grow on the bottom of arches and in caves where there is little to no light.

Thanks in advance to all you ID guru's out there.

 

[rDr4g0n]

featherduster and pineapple sponge, aka q-tip sponge.

 

[music man]

These are indeed quite common, ordinary hitch hiking feather dusters. quite often the tube is actually in the rock to make the animal feel even safer. both are quite beneficial to a natural reef.