Annelid, a member of a large phylum of worms, most of whose members have segmented, tubular bodies. The name comes from the Latin word for "little ring," and refers to the ring-like segments, or somites, of the body. Most species have tiny, stiff, hairlike appendages, called setae, on each somite. Annelids include earthworms, leeches, and sandworms. They are found worldwide in the sea, in freshwater lakes and ponds, in brackish water, and in the soil. Annelids vary in length from about 1/32 of an inch (0.8 mm) to 10 feet (3 m). There are more than 9,000 species.

Annelids make up the phylum Annelida. The three classes of the phylum are:

  • Polychaeta. Clamworms, sandworms, tube worms. Many somites and setae. Pair of appendages called parapodia used in locomotion. Most species are marine. Many live in burrows or tubes in the sea bottom along coastlines.
  • Oligochaeta. Earthworms. Few setae; many somites. Most live in soil or fresh water. See Earthworm.
  • Hirudinea. Leeches. Flattened body with suckers at both ends; usually lack setae. Found in fresh water, salt water, or in soil. See Leech.