Annelid, Critical appraisal

Most authors accept the annelids as having three major classes: Polychaeta, Oligochaeta, and Hirudinea. Older systems would place the polychaetes and oligochaetes under the class Chaetopoda because both groups possess setae. Other systems would join the oligochaetes and leeches in a single class, called the Clitellata, because both groups possess a clitellum