On the genus Haploginglymus
Our phylogenetic analysis corroborates the monophyly of the family Niphargidae but shows Niphargus to be paraphyletic as it currently stands (Figs 2; 3). The paraphyly of Niphargus was already suggested by Sket (1981) and implicitly recognized by Cene Fišer and co-workers, who in different molecular phylogenetic papers (Fišer et al., 2008; Hekmatara et al., 2013; Švara et al., 2015; Esmaeili-Rineh et al., 2015; Brad et al., 2015) showed Carinurella, Pontoniphargus, Niphargobates and Niphargellus nested within that genus. In our analysis, Haploginglymus appears also nested within Niphargus conforming a robustly supported monophyletic group. This clade is sister to another one conformed by the English Niphargellus glenniei (Spooner, 1952) and the Irish Niphargus irlandicus Schellenberg, 1932. These two taxa were already recovered as the most basal niphargids in the analyses performed by McInerney et al. (2014) and Brad et al. (2015). The retention of Haploginglymus as a valid genus in this context is thus implausible, especially taking into consideration that its presumed more remarkable diagnostic trait (the unsegmented U3 exopod) is shared also by the monotypic genera Niphargobates and Carinurella. Nevertheless, the former two genera differ remarkably from Haploginglymus in many relevant features, in accord with their peculiar life-styles.
In any event, our analysis recovers all Haploginglymus species conforming a clade geographically restricted to the Iberian Peninsula, where it replaces the rest of niphargids except for two small disjunct areas on both edges of the Pyrenees (Notenboom, 1990). As in Niphargus s.l., this monophylum includes some morphologically aberrant members such as H. morenoi that, if it were not because it displays an unsegmented U3, it would deserve that a new genus was erected to accommodate it. The potential for morphological disparity in Haploginglymus is thus as high as in Niphargus s. l., and would suggest a long, separate evolutionary history between both lineages, enabling Haploginglymus to colonise and adapt to even the most demanding subterranean niches in Iberia. Considering all these pieces of evidence and that Niphargus already accounts with more than 400 valid species, we opt here for the retention of Haploginglymus as a valid genus. As regard Haploginglymus morenoi and its aberrant morphology, our results fully agree with Iannilli et al. (2009) in considering it as a highly modified member of the genus with a peculiar, interstitial lifestyle.