Labronema, Thorne, 1939

4.1. Diversity of the genus Labronema View in CoL

As previously mentioned, the genus Labronema is a highly heterogeneous dorylaimid taxon, with many species not fully conforming to the typical morphological characteristics that define it. This study provides a comprehensive morphological and molecular characterization of Labronema stechlinensis . One remarkable feature of L. stechlinensis is its continuous lip region, which does not fit the general morphological pattern of the genus Labronema , traditionally characterized by species with an offset lip region (e.g., the type species, L. ferox ). However, some species of the genus, referred to as "atypical" by Alvarez-Ortega´et al. (2010), such as L. hyalinum ( Thorne & Swanger, 1936) Thorne, 1939 , and L. thornei Ferris, 1968 , also display a continuous lip region.

The molecular results from this study reveal a closer relationship between L. ferox and L. stechlinensis than between these two species and other Labronema species with an offset lip region, such as L. bidoupense , L. montanum , L. porosum , and L. octodurensis , which were also included in the phylogenetic analysis. These findings support the earlier hypothesis by Alvarez-Ortega´et al. (2010) that the morphology of the odontostyle – strong, longer than lip region diameter and with comparatively wide aperture (about two-fifths its length) – is the most distinctive feature of the genus. This odontostyle pattern is shared by species like L. ferox , L. stechlinensis , L. hyalinum and L. thornei .

Additionally, L. ferox , L. stechlinensis and L. hyalinum share the presence of a female genital system with a long and complex uterus (Alvarez-Ortega´et al., 2010; Pena-Santiago ˜, 2019), which includes an intermediate pars musculosa, a feature currently unknown in L. thornei . This suggests that the morphology of the odontostyle and the genital system, particularly the uterus morphology, holds greater importance as taxonomic characters than lip region morphology. While the lip region may help distinguish species within Labronema , it is not a reliable diagnostic feature for defining the genus.