A new, putatively semisubterranean, Rhithrodytes diving beetle from southwestern Sardinia (Coleoptera: Dytiscidae) Toledo, Mario Bilton, David T. Balke, Michael Schizzerotto, Antonio Villastrigo, Adrián Acta Entomologica Musei Nationalis Pragae 2023 Acta. Ent. Mus. Natl. Pragae 2023-05-06 63 1 125 133 Toledo & Bilton & Balke & Schizzerotto & Villastrigo, 2023 Toledo & Bilton & Balke & Schizzerotto & Villastrigo 2023 [274,545,1557,1581] Insecta Dytiscidae Rhithrodytes Animalia Coleoptera 2 127 Arthropoda species pantaleonii sp. nov.  ( Figs 1–5)    Typelocality. Italy, Sardinia, Carbonia-Iglesias province, Riu Siuru 4 kmNW Domusnovas, 39°21.55′N 08°37.14′E, 260 ma.s.l.  Type material.  HOLOTYPE: J, labelled: “  16.VI.2022 Italy, Sardinia, CI / Riu Siuru,  4 kmNW Domusnovas/ 39°21.55’ N 08°37.14’ E,  260 m/ Balke, Bilton,Schizzerotto & Toledoleg.” ( ZSM), with red holotypelabel and DNA voucher label: “DNA voucher MB8956” ( ZSM). PARATYPE: J same data as holotypeand with red paratypelabel ( CTB).   Description. Habitus. Body shape ( Fig. 2) elongate- -oblong, no discontinuity between posterior angles of pronotum and base of elytra, lateral sides of elytra almost parallel, maximum width just before middle of elytral length; dorsoventrally flat ( Fig. 3A); colouration pale on both dorsal and ventral sides, ventral segments and parts of elytra almost transparent. Appendages uniformly reddish-yellow; eyes small ( Fig. 4A).  Headrelatively large in proportion, anterior margin forming a rather prominent, regular curve. Eyes apparently functional, but small in proportion to head ( Fig. 4A); ommatidia irregular in size, maximum 9 inlongest series. Surface weakly shining, with visibly impressed isodiametric microreticulation and sparse fine punctures ( Fig. 4A). Colouration uniformly reddish-yellow.Antennomeres 3–10 as long as or longer than wide; terminal antennomere slightly darkened.  Pronotumsubrectangular; lateral sides almost subparallel posteriorly, rounded anteriorly; weakly but visibly sinuate in lateral view. Anterior angles rather prominent; lateral rim well developed along each side.Anterior margin with impressed, transverse irregular puncture row; with sparse and fine punctures between lateral rims and disc; disc and scutellar process without punctures; surface with well impressed isodiametric microreticulation. Colouration reddish-yellow, with indistinct infuscations along anterior and posterior margins.  Elytraelongated, almost parallel-sided in anterior half, apical third regularly acuminate; lateral margins straight in lateral view, gently curving anteriorly over approximately basal sixth of length ( Fig. 3A). Microreticulation isodiametric, more impressed than on head and pronotum, with fine and irregular discal punctures arranged longitudinally, most of them bearing yellow decumbent setae. Colouration yellow with wide, poorly defined, weakly darker area posteriorly along suture and slightly expanded apically. Venation of metathoracic wings visible through elytra.  Fig. 2. Sardinian  Rhithrodytesspecies. A–  R. pantaleonii sp. nov., paratype, dorsal habitus; B –  R. sexguttatus(Aubé, 1838), dorsal habitus; C –  R. pantaleonii sp. nov., holotype, male genitalia; D –  R. sexguttatus(Aubé, 1838), male genitalia. In C & D, images represent, from left to right: median lobe, lateral view; median lobe, ventral view; median lobe apex; paramere. Scale bars A & B = 1 mm; C & D = 100 μm.  Fig. 3. Sardinian  Rhithrodytesspecies, lateral view.A –  R. pantaleonii sp. nov., holotype; B –  R. sexguttatus(Aubé, 1838). Scale bar = 1 mm.  Fig. 4. Sardinian  Rhithrodytesspecies, details of head and compound eyes.A –  R. pantaleonii sp. nov., holotype; B –  R. sexguttatus(Aubé, 1838). Scale bar = 100 μm.  Legs. Metatibiae and metatarsi slender and quite long, with very sparse natatorial setae on inner face. Pro- and mesotarsi not strongly expanded; protarsal claws unmodified.  Venter( Fig. 2A) uniformly reddish-yellow; entirely isodiametrically microreticulated, with additional impressed pits. Prosternal process elongate, rounded apically, barely touching anteromedial metaventral process. Metacoxal lines clearly visible, reaching metaventrite. Epipleuron quite abruptly narrowed before mid-length; oblique carina visible near shoulder. Abdominal ventrites II and III fused with suture barely visible.  Male genitalia. Median lobe ( Fig. 2C), straight in lateral view, with apical hook strongly developed; parallel-sided in ventral view, with acuminate tip visible at apex; acuminate tip strongly developed and clearly visible in ventro-apical view. Parameres ( Fig. 2C) elongate, with narrow, rounded, setose apex.  Measurements. Holotype: BL = 2.7 mm; BL-H = 2.35; EW = 1.2 mm. Paratype: BL = 2.7 mm; BL-H = 2.35; EW = 1.2 mm.   Differential diagnosis.An oblong, flat, almost parallel sided  Rhithrodytes( Fig. 2), with small eyes in proportion to the head. Colouration uniformly pale yellowish-reddish (note that the holotypein Figs 3& 4has darkened somewhat following DNA extraction; for more accurate representation of colour, see Fig. 2A). Natatory setae reduced. On the basis of these characters,  Rhithrodytes pantaleonii sp. nov.has a very distinctive external morphology and cannot be confused with any other species of the genus. The male genitalia ( Fig. 2C) are rather similar to those of  R. sexguttatus( Fig. 2D), differing by the straighter profile of the median lobe in lateral view, with a narrower apical hook, by the narrower, more strongly acuminate apex of the median lobe in ventral view, and by the narrower apex of the parameres.   Etymology.The new species is dedicated to Prof. Roberto Pantaleoni (University of Sassari), who kindly supported our trip in Sardinia. It is a noun in the genitive case, standing in apposition.   Ecology.The Riu Siuru is a small, rocky lowland stream, flowing in a North-South direction over a calcareous substrate. Due the relative drought conditions in Spring- Summer 2022, we found the stream partially dried out and therefore focused on a ca. 15 mreach which had numerous residual pools and some flow ( Fig. 5). Areas immediately above and below this stretch were found to be entirely dry. The new species was collected by digging between gravel and sand, very close to the water’s edge and was very rare or at least difficult to find with hand nets. Other associated aquatic Coleopterawere Gyrinidae:  Gyrinus urinatorIlliger, 1808,  Gyrinus caspiusMénétriés, 1832; Dytiscidae:  Agabus binotatusAubé, 1837,  A. rufulusFairmaire, 1859,  Colymbetes schildknechtiDettner, 1983,  Meladema lepidopteraBilton & Ribera, 2017,  Bidessus minutissimus(Germar, 1824),  B. saucius(Desbrochers, 1871),  Hydroglyphus geminus(Fabricius, 1792),  Hydroporus analisAubé, 1838,  Graptodytes exsanguis(Bedel, 1925),  G. flavipes(Olivier, 1795),  Stictonectes optatus(Seidlitz, 1887),  Deronectes moestus moestus(Fairmaire, 1858),  Scarodytes fuscitarsis(Aubé, 1838); Hydrophilidae:  Laccobius neapolitanusRottenberg, 1874,  Anacaena globulus(Paykull, 1798),  Limnohydrobius convexus(Brullé, 1835); Hydraenidae:  Hydraena sardoaBinaghi, 1961,  H. subsequensRey, 1886,  Limnebius perparvulusRey, 1884,  L. mucronatusBaudi, 1872,  Ochthebius dilatatusStephens, 1829; Limnichidae:  Pelochares versicolor(Waltl, 1838). Of these,  Graptodytes exsanguisand  Hydraena sardoawere the most abundant. 2022-06-16 ZSM Toledo Italy 260 39.359165 Riu Siuru 11 8.619 2 127 MB8956 2 Sardegna holotype