yeah they are one o many types of flatworms that come in on live rock and parasitize soft corals, such as mushrooms and leathers and such. iceman, you might want to check over your devisl hand and toadstols as well to see if there are any of these guys crawling over them. the really dont harm anythign, but can grow to plague proportions and can smother some sessile inverts such as shrooms, blocking them from the light and thus causing them to die. i have had luck in the past using 6 line wrasses, arrow crabs, and even mandarinfish to control them biologically. if you can ice, i would start a siphon and just suck the little punks into a bucket through some plastic tubing, then you cna keep your eye out an dany other that show up, suck em up as well!
good luck
jon