A review of molecular markers used for Annelid phylogenetics.

Annelida, one of the most successful animal phyla, exhibits an amazing variety of morphological forms. Disparity between some of the forms is so great that until molecular tools were used, some annelid lineages (for example, echiurids and pogonophorans) were not commonly recognized as belonging to the group. Although it is easy to assign annelids to a given family, understanding the deeper relationships within the group has been difficult. The main working hypothesis for annelid phylogeny is based on morphological cladistic analysis. However, the recent work using molecular tools has caused a revision of our view of annelid evolutionary history. For example, Scolecida and Palpata appear not to be natural groups, and the phylogenetic positions of some aberrant taxa (for example, Siboglinidae, Poeobius, Pisione) have been determined. Herein, we discuss some of the main molecular markers that have been used to elucidate annelid phylogeny and the contribution that such work is making to our understanding. A table highlighting the molecular literature and the genes used is included.