Aquatic Coleoptera of North Oman, with description of new species of Hydraenidae and Hydrophilidae Author Ribera, Ignacio Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), Passeig Maritim de la Barceloneta 37, E- 08003 Barcelona, Spain; Author Hernando, Carles P. O. box 118, E- 08911 Badalona, Catalonia, Spain; e-mail: leptotyphlus @ gmail. com Author Cieslak, Alexandra Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), Passeig Maritim de la Barceloneta 37, E- 08003 Barcelona, Spain; text Acta Entomologica Musei Nationalis Pragae 2019 2019-06-24 59 1 253 272 journal article 8140 10.2478/aemnp-2019-0021 726682f3-9eac-4961-ac4d-d8b8679e8211 1804-6487 4488950 ABBA2B4F-8B60-41E2-B80B-45861F974B23 Hydraena ( Hydraena ) naja sp. nov. ( Figs 14 , 18 ) Type locality. Source of wadi Bani Awf in Jebel Al-Hajar, Oman (Loc. 4; Figs 1 , 5, 6 ). Type material. HOLOTYPE : ♁ ( NHMW ), “4 Oman 6.4.2010 J.Al-Akhdar // source of wadi Bani Awf , on rock // N23 10 36.2 E57 24 34.1 1300m // Ribera, Cieslak & Hernando leg.”, aedeagus dissected and mounted in DMHF on a transparent card, with holotype label . PARATYPES ( 210 spec. ) ( CCHB , IBEB , MNCN , NHMW , NMPC ): 15 ♁♁ 13 ♀♀ , same data as holotype, with paratype labels; 181 spec. , “3 Oman 6.4.2010 J.Al-Akhdar // rd. Tanuf-Hat,residual pools in wadi // N23 05 36.2 E57 25 56.6 1307m // Ribera, Cieslak & Hernando leg.” ( 1 spec. used for DNA extraction, voucher number IBE-RA97, sequences published in TRIZZINO et al. 2013 as “ Hydraena sp. OMA ”), with paratype labels; 1 ♁, “12 Oman 9.4.2010 1 km W Qalhat // residual pools in wadi // N22 41 25.4 E59 22 03.0 88m // Ribera, Cieslak & Hernando leg.”, with paratype labels. Description. Habitus of male as in Fig. 14 ; body length: 2.30–2.75 mm , width: 0.90–1.10 mm . Elytra, legs, palpi and antennae reddish brown; pronotum darker except for anterior margin, head almost black. Apex of maxillary palpi dark brown. Anterior margin of labrum deeply excised, with coarse punctures. Clypeus entirely densely punctate, matt. Central area of frons less densely punctate, with fine sparse pubescence between punctures; lateral parts of frons (ocular groove) deeply impressed, densely micropunctate. Pronotum distinctly cordiform, anterior margin concave. Surface very densely punctate, interstices densely micropunctate. Median longitudinal impression and oblique posterior admedian grooves shallow. Sublateral groove deep. Elytra elongate, subparallel-sided, with about 15 rows of punctures, with nine to ten rows between suture and shoulder; rows usually very regular, except for an admedian area in anterior third and apical area; punctures small, very densely arranged with small recumbent whitish setae; intervals narrow, very slightly convex, glabrous. Explanate margin of elytra well developed, not reaching elytral apex, weakly serrate; elytral apices more or less separately rounded. Male meso- and metatibiae with apical expansions on ventral side, larger on metatibiae. Female with unmodified tibiae. Ventral surface covered with a very dense short pubescence, forming a plastron except for the last abdominal ventrites and two longitudinal glabrous areas on metaventrite; abdominal ventrites with a dense fringe of setae on posterior margin. Aedeagus as in Fig. 18 . Differential diagnosis. The species seems to be most closely related to H. verstraeteni Ferro, 1984 from south Iran ( Hormozgan ) ( FERRO 1984 , JÄCH 1992 , SKALE & JÄCH 2011 ), based on the external morphology and the male genitalia. Based on the studied material both species cannot be separated on its external morphology, and only differ in the shape of the median lobe and associated appendages of the male genitalia (see fig. 41 in JÄCH 1992 ). Both species differ 5.3% in their COI-5 gene, based on a specimen of H . verstraeteni from south Iran (voucher IBE-AN461, prov. Khuzestan , Behbahan, Garmabeh river, 5.v.2011 E. Irani leg.). Phylogenetically both species are included in a clade with H. persica Janssens, 1981 , H. dochula Jäch & Skale, 2009 and related species, in turn related with the species of the H. grandis , H. rufipes and H. pulchella groups ( TRIZZINO et al. 2013 and unpublished results). Etymology. Named after the elapid snake genus Naja (cobras), in reference to the shape of the enlarged setae of the aedeagus ( Fig. 18 ), resembling a cobra in its characteristic threatening position. Noun in singular nominative, standing in apposition. Notes on the habitat. The species was most commonly found in two localities, residual pools in a wadi (locality No. 3) and the source of wadi Bani Awf (locality No. 4). The residual pool ( Fig. 4 ) was the result of disruption by road works of a (by then) dry wadi, producing a pool with a diameter of ca. 3–4 m with muddy and sandy substratum and very turbid water. The species was here very abundant, together with Ochthebius bernard sp. nov. and Hydraena quadricollis Wollaston, 1864 (see below), plus other species in lower numbers. The source of wadi Bani Awf ( Figs 5, 6 ) is a spring on a rocky surface, apparently at least partially artificially excavated to form a small tunnel through which the water is diverted to an artificial open channel that goes down the valley. When the locality was visited (6 th April) all the water was diverted through the channel, but occasionally the water should overflow it and run through a natural rocky bed, that at the time of our visit was completely dry. The distance between the spring and the channel was at most ca. 10 m , with a rocky substratum with a thin layer of sand and gravel, with some green filamentous algae. Despite the reduced dimensions of the habitat the diversity was remarkably high, with six species of Hydraenidae , all of them endemic to Oman and the UAE and three of them newly described here ( Hydraena naja sp. nov. , H. gattolliati , H. putearius , Ochthebius bernard sp. nov. , O. alhajarensis sp. nov. , O. wurayah ), in addition to Copelatus gestroi , Nebrioporus mascatensis and Hydroglyphus sinuspersicus . Distribution. Found in the Al Hajar mountains, with an isolated specimen in a wadi in the coast of the Gulf of Oman ( Fig. 1 ).