Taxonomy of water beetles in the genus Hydrochus Leach, 1817, from Bolivia, Brazil and Paraguay (Coleoptera: Hydrochidae) Author Perkins, Philip D. text Zootaxa 2021 2021-06-28 4994 1 1 93 journal article 10.11646/zootaxa.4994.1.1 1175-5326 5043261 107FCA64-345F-40A4-99D3-5C1441EEAD93 Hydrochus canalis , new species Figs. 3 , 30 , 54 , 70 Type Material. Holotype (male): Brazil : Mato Grosso , “ Rio Caraguata , M. Grosso , Brazil, IX-53, 21°48’S , 52°27’W , 400M alt., Fritz Plaumann leg.” ( NMNH ) . Paratypes (4): Paraguay : Alto Parana , Estancia Dimas , ( 25°33’S , 55°13’W ), 24–25.xi.2004 , leg. U. Drechsel (2 NMW ) ; same locality, 17–22.ii.2005 , leg. U. Drechsel (2 NMW ) . Differential Diagnosis. A member of the H. collaris group, recognized by the combination of the moderate size (ca. 3.14 mm ), the deep cervical groove, and the male genitalia ( Fig. 30 ; described below). Differentiation from other members of the H. collaris group will require dissection of males. Refer also to the H. collaris species group section. Description . Size: holotype (length/width, mm): body (length to elytral apices) 3.14/1.10; head width 0.75; pronotum l/w 0.70/0.70; PA 0.70; PB 0.62; elytra 1.97/1.10. Habitus as illustrated ( Fig. 30 ). Dorsum grey to silver, with moderately strong iridescence, cervical groove black, elytra with black spots. Legs testaceous to brown, with tibiofemoral joints darker. Punctation on elytra ca. 2x that of pronotum. Elytra interstriae ca. 1–2x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th moderately raised, moderately elongate, ca. 6–7 punctures in row on each side. Head with deep curving cervical groove from side to side behind eyes, groove punctate, cervical area behind groove impunctate, shining, with very fine, low, closely set longitudinal raised lines. Pronotum length and width ca. equal, widest at anterior margin, narrowed at base, sides straight or extremely slightly arcuate, smooth; anterior margin arcuate, fitting into cervical groove; depressions moderately deep, anteromedian deepest, very slightly more densely punctate than reliefs between depressions. Elytra with spaces between strial punctures ca. 0.5–1x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with small angulation, impunctate area of apices rather large. Ventral characters: Mentum coarsely densely punctate, with large, deep basomedian fovea; submentum finely sparsely punctate, with two deep foveae, posterior margin markedly arcuate. Male genitalia ( Fig. 30 ) general characters: genitalia elongate, about six times as long as widest part, basal piece slightly longer than parameres (ratio ca. 22/21); parameres in distal ½ much narrower than aedeagus, in proximal ½ distinctly wider than aedeagus, paramere tips extending very slightly beyond aedeagus tip, arcing toward midline, widely separated from aedeagus; aedeagus widest apically, becoming narrower from apical area to basal area, membranous area large; basal piece wider in dorsal/ventral views than lateral view, parallel-sided in dorsal/ventral views, in lateral view very slightly arcuate, lacking any process of sclerotized rim. Dorsal surface: adtl at ca. distal 1/3; pdmm widely separated from alm, except at base; adbl small. Ventral surface: avtl at ca. distal 1/3; pvmm very similar to pdmm, except basal part overlapping alm slightly. Etymology . Named in reference to the deep cervical groove.