in my live rock, there are these red caterpillar/centipede looking things, what are they?

Question

this is in a saltwater aquarium

Answer 1

It sounds like it might be some kind of a bristleworm - here's a link to what the ones in my tanks look like: http://www.kwajaleinscubaclub.com/photos/johnson-critters/Bristleworm.jpg

There are some types that eat corals, but these are hardly ever seen. The orange-salmon colored ones like the one in the photo bore through the live rock, increasing the calcium in the tank & burrow into the substrate to eat any food missed by the other animals. Just be careful when you're moving your live rock around - the bristles on these guys sting!

Here's an article about the destructive type and how to get rid of them: http://saltaquarium.about.com/cs/msubpestbworm/a/aa102198.htm

And see the last question & answer in this link: http://www.marineaquariumadvice.com/librarysaltwaterfactsjanuary2000.html

Answer 2

Could it be bristle worms maybe?