Haploginglymus Mateus and Oliveira-Mateus, 1958, is a genus of niphargid amphipod endemic to the fresh inland subterranean waters of the Iberian Peninsula (Spain and Portugal). It is found in caves, wells and the interstitial medium associated to riverbanks, but apparently avoids the brackish waters of coastal aquifers. First discovered in wells from the lower course of river Douro in NW Portugal, the genus displays a broad distribution across the entire Peninsula, where it is one of the most common subterranean crustaceans (Notenboom, 1990). The genus was originally distinguished from Niphargus Schiödte, 1849 – by far the largest genus among freshwater amphipods (408 valid species; Lowry, 2010) – based on the display of an unsegmented (vs. 2-segmented) exopod on uropod III. Nevertheless, two additional niphargid genera described later on, both monotypic, viz. Carinurella Sket, 1971, and Niphargobates Sket, 1981, share with Haploginglymus the same condition of uropod III, although both can be readily told apart from Haploginglymus based on other features (Sket, 1971; 1981).
Despite its almost generalised distribution across Iberia, only five species of Haploginglymus have been formally described thus far (Mateus and Oliveira-Mateus, 1958; Stock, 1980; Karaman, 1986; Pretus and Sabater, 1990; Iannilli et al., 2009). Aside the morphologically aberrant H. morenoi Iannilli, Minelli and Ruffo, 2009, which displays a modified spatulate maxillipedal palp, slender gnathopods and strongly sexually-dimorphic gnathopod II, all show a rather uniform, ordinary Niphargus-like aspect. Anyway, molecular analyses under way suggest the genus mirrors the condition described elsewhere for Niphargus, where each species displays a very reduced distribution and the few presumed widespread species correspond in fact to complexes of stenochorous cryptic species (Trontelj et al., 2009; Meleg et al., 2013).
As a first step to explore the diversification of Haploginglymus in Iberia, we combine herein morphology and molecular traits to describe a new species from southern Spain. We use DNA sequences of three gene fragments (nuclear ribosomal 28S and protein-coding Histone 3, plus mitochondrial Cytochrome c Oxidase subunit I) to assess the distinctiveness of this Iberian genus in front of the rest of niphargids, and the placement of the morphologically aberrant H. morenoi within Haploginglymus. In addition, we have found the Pseudoniphargidae Karaman, 1993 to be the closest relative to niphargids, which gives a new perspective to the debate on the origin, diversification and biogeography of this extremely diversified family of continental water amphipods.