Bristle worms are a large group of worms with many different ways of feeding, moving, and reproducing. They are found in all oceans from shallow intertidal reefs to deep depths. They live on or burrow into sand, mud, shell debris, rocks and coral rubble. Some eat their way through muddy sediments, some eat algae and others are accomplished predators. They are a great favourite food of fish, crabs and are hunted by predatory snails.

• To be an annelid worm with paddle-shaped feet and many fine bristles or hairs extending from each segment of your body.
• A free-living worm that moves about in snake-like motions, using the circular and longitudinal muscles in each segment of your body.
• A mouth that you can extend some way outside of your body. Your mouth may be soft and sac-like or have hard teeth.
• Some sensory structures on or near your head

Squirt worms, rag worms, fire worms, blood worms, bait worms, scaleworms, sea mice, bamboo worms, sand worms

Bristle worms come in a great variety of sizes and colours, but most are several times longer than wide. Their bodies have bilateral symmetry, and most of their body segments look identical. You can usually tell the back from the front end by the presence of a pair (or several pairs) of eyes. Some species also have long, sensory tentacles near the head which help them find food. A closer look at some of the larger species will reveal a pair of fleshy paddles on each segment (parapodia) which can be very small in some species. These serve much the same function as feet, helping the worm move about in s- shaped movements.

Bristle worms are found in all oceans, from intertidal reefs to the deep ocean. They are not often seen out in the open where they might easily be eaten by a fish or crab, but can be found under rocks and in cracks and crevices. Burrowing species are usually found in the upper 5 cm of sediment.

Bristle worms eat in a variety of ways. Burrowing species plough through the sediment, extending their sac-like mouths rhythmically. Sediment particles stick to the mucus around the mouth and are sucked into the body. As the sediment passes down the worm's tubular gut, the food attached to the sediment is digested, and cleaner sediment is expelled at the back of the worm. Species with scissor-like teeth can cut off and eat bits of algae or dead animals they find. Other species with strong jaws chase living prey, including smaller worms, crustaceans and snails

Fish are the main predators on worms, and worms have been shown to be an important part of the diet of fish in some habitats. In the tropics worms are also hunted by cone snails (Family Conidae) which have evolved a special harpoon-shaped tooth which they use to spear worms. Crabs probably also eat worms when they can find them.

Worms grow by widening each segment and by growing new segments which are added near the back end of the worm. They can grow quickly in the right conditions, from a few millimetres long to three or four centimetres long in a year, depending on the species. Worms are also very good at repairing parts of their bodies. Should they lose only their head to a hungry fish, they can regenerate it, but it will take a while to grow as large as the one they lost. Bristle worms have separate sexes, but you generally can't see the differences unless they are ready to reproduce. Eggs and sperm are produced in the worm's back section. When ripe they can be released in different ways, depending on the species. In most species, the body wall simply opens up and the eggs or sperm come flooding out, to be fertilised in the water. In some families of worms that live in the tropics, the segments containing the eggs and sperm break off from the rest of the worm and float up in the water, where they are released. Sometimes this is proceeded by the adult worm swimming up into the water. This spawning takes place during particular combinations of tide, phase of the moon and water temperature, which reef-dwelling people can predict. They scoop up the segments containing eggs and sperm and eat them! Fertilised eggs change quickly into swimming, top-shaped larvae which become part of the planktonic community. After they have grown to look more like a worm and have about nine segments they settle out of the water and look for a suitable place to live.

Bristle worms generally live by themselves, and some of the larger, predatory species may defend the territory they live in. They generally don't have parasites, but a few species live in association with starfish and other invertebrates.

Fishers are the main group of people who collect worms for bait. On the east coast of Australia there is an industry for live bait worms which is based on only a few species which are collected from Queensland and northern New South Wales. Collectors say that big worms are getting harder to find, but no research has been done to determine if this is true, or if the targeted species are becoming endangered. In estuaries in New South Wales fishers collect squirt worms for bait, but this species (Australonereis ehlersi) is fragile and is not collected commercially. One type of crawling bristle worm can irritate your skin if you pick it up. The bright red colour of fire worms should be enough warning that their fine, hair-like bristle contain a skin irritant. The larger species of crawling worms with jaws can deliver a mean bit to a human hand if they are pestered.