Critters in tank, what are they?

I had a "breakout" of these small white puffy rice looking things that are
kinda mushy and are scraped off the glass easily...
They are also inside my protien skimmer just living happily.

A few of them developed far enough to have some kind of tentacles like a
small feather duster of some sort, any ideas what they are, are they bad,
good ... what?
Water tests show water is perfect, the tank is about 7 months old with lots
of live sand and live rock to start it out, but nothing was added to the
tank besides the sand and rock for 2 months. Few fish in there now, lots of
crabs/snails and some corals (mushroom, torch, ricordia mushroom), 2 feather
dusters..

I had a simular breakout just before these guys of small white spiral
looking worms that harden and attached themselfs to glass, but they seem to
be no harm either.

I would love to know what these are, they dont seem to be bad but I could be
wrong, they were on the back of my tank only, but I think something ate them
off of the tank, but they are still rampant in my sump as the pictures show
below:

http://www.onlocke.com/tank/tank2.html

Some older pics of tanks (without the critters):
http://www.onlocke.com/tank/tank.html

-L