Molecular phylogeny of earthworms (Annelida:Crassiclitellata) based on 28S, 18S and 16S gene sequences

Abstract

Relationships among, and content of, earthworm families have been controversial and unstable. Here we analyse molecular data from 14 Crassiclitellata families represented by 54 genera, the non-crassiclitellate ‘earthworms’ of the Moniligastridae, plus several clitellate outgroups. Complete 28S and 18S gene sequences and a fragment of the 16S gene analysed separately or in concatenated Bayesian analyses indicate that most previously proposed suprafamilial taxa within the Crassiclitellata are para- or polyphyletic. There is strong support for the Metagynophora, which consists of the Crassiclitellata and Moniligastridae. The most basal within-Clitellata branch leads to the small families Komarekionidae, Sparganophilidae, Kynotidae, and Biwadrilidae, found in widely separated areas. A clade composed of Lumbricidae, Ailoscolecidae, Hormogastridae, Criodrilidae and Lutodrilidae appears near the base of the tree, but Criodrilidae and Biwadrilidae are not closely related because the former is sister to the Hormogastridae + Lumbricidae clade. The Glossoscolecidae is here separated into two families, the Glossoscolecidae s.s. and the Pontoscolecidae (fam. nov.). The Megascolecidae is monophyletic within a clade including all acanthodrilid earthworms. There is strong support for the Benhamiinae (Acanthodrilidae s.l.) as sister to Acanthodrilidae + Megascolecidae, but taxon sampling within other acanthodrilid groups was not sufficient to reach further conclusions. The resulting trees support revised interpretations of morphological character evolution.’