Abstract
Recent inferences of phylogeny from molecular characters, as well as a reexamination of morphological and biological characters, reject the monophyly of the nematode genus Koerneria Meyl, 1960 (Diplogastridae). Here, Koerneria sensu lato is revised. The genus, which previously consisted of 40 species, is separated into three genera. Almost all of the transferred species are moved to the resurrected genus Allodiplogaster Paramonov & Sobolev in Skrjabin et al. (1954). Koerneria and Allodiplogaster are distinguished from each other by a weakly vs. clearly striated body surface, an undivided vs. divided stomatal cheilostom, and arrangement of the terminal ventral triplet of male genital papillae, namely in that v5 and v6 are paired and separated from v7 vs. v5–v7 being close to each other. Allodiplogaster is further divided into two groups of species, herein called the henrichae and striata groups, based on both morphological and life-history traits. The henrichae group is characterized by papilliform labial sensilla and male genital papillae, a conical tail in both males and females, and an association with terrestrial habitats and insects, whereas the striata group is characterized by setiform labial sensilla and male genital papillae, an elongated conical tail in both sexes, and an association with aquatic habitats. A second genus, Anchidiplogaster Paramonov, 1952, is resurrected to include a single species that is characterized by its miniscule stoma and teeth, unreflexed testis, and a distinct lack of male genital papillae or stomatal apodemes. Lastly, one further species that was previously included in Koerneria sensu lato is transferred to the genus Pristionchus Kreis, 1932. The revision of Koerneria sensu lato is necessitated by the great variability in its subordinate taxa, which occupy a variety of habitats, in addition to the increased attention to Diplogastridae as a model system for comparative mechanistic biology.
Highlights
Koerneria Meyl, 1960 heretofore consisted of 40 nominal species, following the revision by Sudhaus and Fürst von Lieven (2003) and including species described since (Suppl. material 1)
For the previous, wider definition of Koerneria the name Koerneria was itself a junior synonym of Allodiplogaster, the name Koerneria is retained for a group of six described species, all of which are unambiguously unified by morphological characters and which are represented by a clade not nested within any other valid genus
Species of Koerneria in the revised sense are apparently the sister group to most or all species of Diplogastridae, with the possible one exception of Leptojacobus dorci, and the revision of this genus will be useful for ongoing research on the family as a comparative model system
Summary
Koerneria Meyl, 1960 heretofore consisted of 40 nominal species, following the revision by Sudhaus and Fürst von Lieven (2003) and including species described since (Suppl. material 1). Biological characters are variable for the genus, which contains terrestrial species isolated from rich soil environments, associates of several different groups of insects, and aquatic species Such a diversity of ecologies raises the question of whether distinct subgroups of the genus can be identified and corroborated by independent characters. A taxonomic reorganization of Koerneria sensu lato (= Koerneria sensu Fürst von Lieven 2008) is needed Such a revision is of particular importance for ongoing studies of the natural history of the genus and its relatives (e.g., GiblinDavis et al 2006, Kanzaki et al 2009) as well as comparative research more generally in Diplogastridae (e.g., Mayer et al 2009, Ragsdale et al 2013), as Koerneria sensu lato includes taxa that are sister groups to most other known species in the family. Revision of the paraphyletic genus Koerneria Meyl, 1960 and resurrection
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