Worm?

[pat18]

I need some help, when i was looking in my refugium, i saw what i think was a worm, both front and back were yellow, and the center was black, and between the center and each side it is orange.
( yellow--->Orange--->Red--->Black<---Red<---Orange<---Yellow). I was going to take a picture but i do not know where it went now. If anyone could tell me what it is and what i should do about it, it would be very helpful, because don't want anything to go bad. Also it was about 1/2" long.