There is a dark colored slug-looking invert crawling on my glass. It looks black and greyish with small white tenticles, almost like spines that it appears to move with. It is worm-shaped and VERY slow moving.
Yeah probably a bristleworm. There's alot of species and probably many dozens in your tank. Good things. Help stir up the sand bed. There's a good article right now over in www.reefcentral.com/ that you can check out if you want to learn more.
I've looked in every book I know and I've nor found a picture of what Im looking at.
Its NOT a bristleworm. Not only does it not behave like one, but it does not have the same characteristics.
THe worm is very fat, probably 1/4 of an inch in diamete. The white tenticles are not small and planced in even rows. They are randomly asorted on his body and they are long, probably nother 1/4 inch in length. THey are white and fade to black down on the body.
It's some kind of Nudibranch. I have one in my tank that is kinda greenish-brown, spiky and crawls on the glass. Probably some long lost twin brother =)
If they are nudibranchs, you may be able to find a pic on this site...or at least something close enough to tell you for sure: http://www.divegallery.com/