Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the oligochaetes, which include the earthworm, and like them have soft, muscular, segmented bodies that. Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida. They are closely related to the. Please SUBSCRIBE NOW! More - all Leeches out to get you? Warning, this film contains images of human blood. Humans have long had an unusual mutualistic relationship with leeches. Leeches are segmented worms in the Subclass Hirudinea that are usually ectoparasitic. They belong to the Class Clitellata (along with earthworms, Subclass. Leeches are worms that live in water or on land and feed by sucking blood from fish, frogs, lizards, birds or, if they get the chance, larger. Distant cousins of the earthworm, most leech species are parasites that feed on the blood of animals and humans alike. They are often found in. Leeches are parasitic worms found on every continent except Antarctica. Many live on blood (some need just one meal a year), earning them the. leech, (subclass Hirudinea), any of about species of segmented worms (phylum Annelida) characterized by a small sucker, which contains the mouth. Which I suppose it is. Thousands of years since leeches were first employed for medicinal purposes, and a century since “leech mania” saw blood-.