[3][4] Despite the common name "freshwater leeches", species are found in both sea and fresh water.

[9] Instead of jaws and teeth, Rhynchobdellidae have protrusible proboscises, which they use to penetrate the host's skin.

[citation needed] Sanguivorous species usually feed on a variety of other animals, using their proboscis to host's skin.

[2] Predatory Rhynchobdellidae have digestive enzymes that help break down their prey, which usually consists of small invertebrates such as insect larvae or amphipods.

[4] The Piscicolidae occur in both freshwater and seawater, have cylindrical bodies, and a usually well-marked, bell-shaped, anterior sucker.