Towards an integrative revision of Haplotaxidae (Annelida: Clitellata)

The classification and phylogenetic position of Haplotaxidae, an enigmatic family of clitellate worms, have long been discussed. We estimate the phylogeny for Clitellata as a whole, using a taxon sample adhering to current definitions of Haplotaxidae and including species attributable to Haplotaxis, plus a representation of other clitellates. Sequences of five markers, 4087 bp in total, were analysed by Bayesian Inference. A well-supported tree shows that Haplotaxidae is polyphyletic, consisting of at least five separate clades scattered among other clitellate lineages. We redefine Haplotaxidae s.s. to only include Haplotaxis, and erect four new families: Pelodrilidae Martin et al.fam. nov. for Pelodrilus, Hologynus, and Delaya; Haplotaxoididae Martin et al.fam. nov. for Haplotaxoides Fend gen. nov., with Haplotaxoides decipiens Fend sp. nov. and Haplotaxoides tehama Fend sp. nov.; Limpluvidae Martin et al.fam. nov. for Limpluvia setoensis Fend & Torii gen. et sp. nov.; and Ohtakianidae Martin et al.fam. nov. for Ohtakiana kakidaensis Fend & Torii gen. et sp. nov. To adhere to standard classification systems, we assign all five families to separate orders, Pelodrilida ord. nov., Haplotaxoidida ord. nov., Othakianida ord. nov., Limpluvida ord. nov., and Haplotaxida. Haplotaxidae s.s. and Pelodrilidae seem to belong to an incompletely resolved group also including lumbriculids, leeches, and earthworms. Moreover, a close relationship between Limpluvia, Ohtakiana, and the lumbriculid-hirudinean clade (i.e. taxon Lumbriculata) is strongly supported, whereas Haplotaxoididae are placed more basally in the clitellate phylogeny than the other haplotaxids s.l., their exact position remaining unresolved. The analysed Holarctic Haplotaxis populations (representing up to 10 species) appear separated more by geography than by obvious morphological characters.