1. (n. pl.) An extensive artificial division of the animal kingdom, including the parasitic worms, or helminths, together with the nemerteans, annelids, and allied groups. By some writers the branchiopods, the bryzoans, and the tunicates are also included. The name was used in a still wider sense by Linnaeus and his followers.

2. (n. pl.) A more restricted group, comprising only the helminths and closely allied orders.