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 austrinus , new species Figs. 3 , 16 , 59 Type Material. Holotype (male): Brazil : Rio Grande do Sul , “ Pelotas , 9 Jan. 1956 , R. G. do Sul—Brasil, C. Biezanko leg.” ( NMNH ) . Paratypes : Same data as holotype (5 NMNH ) . Differential Diagnosis. Among Brazilian species, recognized by the combination of moderate size (ca. 3.14 mm ), the deep pronotal depressions, and the male genitalia ( Fig. 10 ; described below). This species has a generalized Hydrochus habitus; reliable determinations will require dissection of males. Description . Size: holotype (length/width, mm): body (length to elytral apices) 3.14/1.03; head width 0.71; pronotum l/w 0.66/0.69; PA 0.64; PB 0.61; elytra 2.04/1.03. Habitus as illustrated ( Fig. 16 ). Body size moderate (ca. 3.14 mm ). Dorsum dark brown, with very slight or no iridescence, elytra with black spots. Body form narrow (l/w ratio ca. 41/24). Legs brown, with tibiofemoral joints darker. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 1–1.5x strial puncture diameter. Interstria 9 th slightly more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th not raised. Pronotum very slightly wider than long (ratio ca. 36/35), widest slightly behind anterior margin, narrowed at base, sides very weakly sinuate, smooth; anterior margin slightly bisinuate; depressions moderately deep, much more densely punctate than low 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 slight angulation. Ventral characters: Mentum punctate, with central depression; submentum with two foveae. Male genitalia ( Fig. 16 ) general characters: genitalia elongate, length ca. 6x greatest width, basal piece and parameres ca. equal in length; paramere tips extending very slightly beyond aedeagus tip, medial margins beyond aedeagus tip parallel, plsa very small, lateral margins between plsa and apex straight; parameres in dorsal/ventral views very narrow over distal 2/3, straight; in lateral view parameres arcuate toward dorsad in distal 1/2, sharply pointed apically; aedeagus moderately wide, sides arcuate, agw at ca. midlength; basal piece in dorsal/ventral views nearly parallel-sided, in lateral view dorsal surface slightly more arcuate than ventral, orifice asymmetrical, margin sclerotized. Dorsal surface: adtl at ca. midlength of aedeagus; pdmm widely separated; adbl moderately large, width slightly less than agw. Ventral surface: avtl very near base, almost at alw; pvmm separation similar to pdmm, neither overlapping alm. Etymology . Named in reference to the geographical distribution, at the southeastern extreme of Brazil .