Filter Creature!

Question
Hi, I am an amateur marine tank/reef keeper. Recently while checking my filter I found an odd white creature swimming about. Its body is white with what look like many legs on the belly and feather like appendages along the length of its back(like a stegosaurus) with darker tips. The head was larger and it moves along the filter sides like a slug or it swims freely by moving both its legs and body sides like flaps. Darned if I know!!!!! I couldn't take a picture but if I saw one I could identify it as the same. Just want to protect my system or be happy its there!  Can you help please?

Answer
Hi Warren. It sounds like you have some sort of a sea slug or nudibranch in your filter. Although these do not have legs and use the same method of locomotion as snails do. You have me stumped! If I could see a picture of it I could 100% identify it for you and you have to understand that a written description is sometimes very difficult to go off of. I can give you a web site that has lots of pictures and information on the different creatures that hitch hike on live rock. They may not have an exact picture of your creature but if you can find an animal that very closely resembles it in body structure and size that would be a good place to start. Do not go by color. Some times color can vary greatly even in the identical species due to the diet and what area of the ocean they were collected from. if you could get a picture I could identify it no problem. Check out this site and if you don't see your creature but something very closely resembling it let me know and I will be able to assist you further!

http://www.chucksaddiction.com/hitchhikers.html