Earthworms and Other Oligochaetes

Earthworms and their relatives, the Oligochaeta, are segmented worms of the phylum Annelida, which is found worldwide from the deepest marine sediments to the soils of city parks and yards. Through most of the twentieth century Annelida was split into polychaetes, oligochaetes and leeches, but the Oligochaeta and Hirudinea, comprising several thousand species, are now recognized as a single clade, called Oligochaeta or Clitellata depending on the author. This clade may even belong inside Polychaeta, which would make Polychaeta synonymous with Annelida. Earthworms and leeches are the familiar annelids for most people, but polychaetes make up the bulk of the diversity of the phylum.