The ones that live under the sand are called sand worms. They can also live under rocks, among piles of broken shells in mud and build their own burrow. Each segment of a bristle worm has a pair of extensions with a bunch of bristles. Many of the worms are free living and eat other marine creatures. Others eat seaweed or eat microscopic food from the sand or mud.
Some of the larger species are called fire worms. The bristles from these species are sharp and can puncture the skin. The bristles then break off and the pain lasts a long time.
This helps these slow moving bristle worms to defend themselves from other hungry sea creatures.
To crawl or swim they wriggle their long bodies like a snake. They have simple eyes on their head. Many birds, fish and other marine animals feed on bristle worms. Fishers use them as fish bait. The larger bristle worms can bite.