an order of a subclass of Hirudinea (leeches). The body length of most species does not exceed 2–3 cm. The anterior part of the digestive tract has been converted into a proboscis, an organ to pierce the cutaneous covering of other animals and suck out the blood, juices, and liquefied parts of their bodies.

Rhynchobdellea are widely distributed. There are two families: Glossiphoniidae and Ichthyobdellidae (or Piscicolidae). In the former the body is severely flattened, almost leaflike; it narrows toward the ends, especially the anterior end. Glossiphoniidae live in freshwaters. They suck the blood of invertebrates and vertebrates. The ova, which are enclosed in thin-walled amorphous cocoons, or the embryos are carried on the abdomen. Some species are parasites of swimming birds. Ichthyobdellidae have a cylindrical or, less commonly, flattened body. The anterior sucker is sharply divided from the rest of the body. Ichthyobdellidae inhabit seas, freshwaters, and brackish waters. They suck the blood of fishes; some species suck the blood of crustaceans and sea spiders. The eggs, enclosed in cocoons, are laid on various underwater substrates. The leeches often are injurious to their hosts.