Placing the forgotten: on the positions of Euenchytraeus and Chamaedrilus in an updated enchytraeid phylogeny (Clitellata : Enchytraeidae)

Abstract

The phylogeny of Enchytraeidae was re-estimated to establish the relationships of the now resurrected Chamaedrilus and Euenchytraeus and to confirm their status as separate taxa. The former Cognettia (Enchytraeidae) was recently revised and split into its two senior synonyms, Chamaedrilus and Euenchytraeus, with the majority of the species transferred to Chamaedrilus. Euenchytraeus was re-established for three species sharing a unique anatomical trait, but has never before been represented in any phylogenetic study. We included representatives from 21 (of 33) valid enchytraeid genera and used three mitochondrial and four nuclear genes. The dataset (4164 base pairs) was analysed using multi-species coalescent (MSC) and maximum likelihood (ML) methods. Chamaedrilus (represented by eight species) and Euenchytraeus (represented by Eu. clarae) were found in a clade together with the monotypic Stercutus. Chamaedrilus was found to be monophyletic with maximum support in both analyses. The ML tree supported Euenchytraeus and Chamaedrilus as sister groups, whereas the MSC tree placed Euenchytraeus together with Stercutus, both with low support. A Bayes factor test weakly supported Euenchytraeus and Chamaedrilus as sister groups over Euenchytraeus+Stercutus. Possible morphological synapomorphies for these genera are discussed, and we conclude that Chamaedrilus and Euenchytraeus are closely related, but their status as separate genera is justified.