Annelida*

The first annelids were formally described by Linnaeus (1758) and we here briefly review the history and composition of the group. The traditionally recognized classes were Polychaeta, Oligochaeta and Hirudinea. The latter two are now viewed as the taxon Clitellata, since recognizing Hirudinea with class rank renders Oligochaeta paraphyletic. Polychaeta appears to contain Clitellata, and so may be synonymous with Annelida. Current consensus would place previously recognized phyla such as Echiura, Pogonophora, Sipuncula and Vestimentifera as annelids, though relationships among these and the various other annelid lineages are still unresolved.