I found a small slug-like creature adhering to the glass in my new aquarium. It is rather small and oval shaped (1/4-1/2 in.). It has two very long "tentacles" (can extend to more to about 5 in.) that are sort of feathery looking. These tentacles are very thin and hair-like. It will slowly extend these tentacles and then retract them very rapidly if they touch something. The creature move very slowly across the glass (1-2 in. per day). It has a mottled light brown coloration. I'll try to get a picture tonight if My camera will cooperate, but I imagine that the tentacles will not show up because they are so fine. Has anyone seen this before? What is it? Should I get rid of it?