Stylodrilus heringianus is a freshwater oligochaete, now with a wide cosmopolitan distribution, which may have been introduced to North America (Mills et al. 1993; Grigorovich et al. 2003). Oligochaetes lack parapodia, and have relatively short setae. They are hermaphroditic, with a few anterior segments modified to form a reproductive section, called the clitellum. At sexual maturity, they have a few modified segments forming a reproductive section, called a clitellum. The worms copulate, and lay fertilized eggs in cocoons. Stylodrilus heringianus is 25-40 mm long, We consider populations of S. heringianus in the Great Lakes to be cryptogenic, and those in the Columbia River (Sytsma et al. 2004) to be introduced. Likely vectors include ballast water, shipments of aquatic plants, and accidental introduction with stocked fishes.