THE XERCES SOCIETY FOR INVERTEBRATE CONSERVATION

Aquatic Invertebrates in Pacific Northwest Freshwater Wetlands
An Identification Guide and Educational Resource

Branchiobdellida is a class in the phylum Annelida, which also includes the Hirudinea (leeches) and Oligochaeta (aquatic earthworms). Branchiobdellida are called crayfish worms because they live on the exoskeleton of crayfish. They resemble leeches, but have only 17 segments instead of the 34 (often subdivided) segments in leeches.

Crayfish worms feed on the microorganisms that live on the surface of crayfish exoskeletons. Given the opportunity, they will also feed opportunistically on scraps of food not ingested by their crayfish host. Almost any species of crayfish can serve as a host for branchiobdellids but some crayfish will try to remove any branchiobdellids that attach.

Size: small to medium
Identifying feature(s): sucker present on at least one end; far fewer segments than leeches
Habitat: live on crayfish exoskeleton
Tolerance to pollutants: tolerant