Phylogeny and evolution of annelida based on molecular data

Abstract

Annelids inhabit diverse habitats from the deep sea to terrestrial soils. Being one of the three animal taxa exhibiting true segmentation, deciphering the evolution of Annelida is crucial to our understanding of the evolution of segmentation. Traditionally, Annelida comprised polychaetes (e.g., lugworms, fanworms, fireworms) and clitellates (e.g., earthworms, leeches). In this chapter, we summarize results regarding the phylogeny and evolution of Annelida that have been obtained in the last years using different sources of molecular data. Results to date support hypotheses in which non-segmented Sipuncula (peanut worms) and Echiura (spoon worms) are part of the annelid radiation, and Clitellata are placed among taxa like the lugworms within polychaetes. The majority of annelid taxa is found within one large clade that split into Errantia and Sedentaria and thus was named Pleistoannelida. On the other hand, the most recent analyses included support for placements of Chaetopteridae (parchment worms), Oweniidae or small, interstitial polychaete families as part of the basal annelid radiation. Based on these results and the fossil record, biodiversity of Annelida most likely originated from an early annelid resembling a crawling form with grooved palps and parapodia with simple chaetae. © 2014 Walter de Gruyter GmbH, Berlin/Boston.