Hydrochus longissimus, Perkins, 2021

Perkins, Philip D., 2021, Taxonomy of water beetles in the genus Hydrochus Leach, 1817, from Bolivia, Brazil and Paraguay (Coleoptera: Hydrochidae), Zootaxa 4994 (1), pp. 1-93 : 29-30

Hydrochus longissimus , new species

Figs. 1 , 44 , 57 , 70

Type Material. Holotype (male): “ BRAZIL: Goiás: Alto Paraiso / Rio Dos Couros, nr. Alto Paraiso (-14.27741 -47.75075); 967 m /; small side stream flowing into river, rock/gravel substrate; 21.ii.2018 / Benetti and team; BR18-0221-01D” ( INPA).

Differential Diagnosis. Among Brazilian species, recognized by the combination of moderate size (ca. 2.76 mm), grey to bronze dorsum, with large black spots, the pronotal depressions moderately large, moderately deep, more densely punctate than almost impunctate reliefs, the pronotal shape, the raised 3 rd and 5 th elytral interstriae, without usual callus, and the male genitalia ( Fig. 44 ; described below). Completely reliable determinations will include dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.76/1.03; head width 0.67; pronotum l/w 0.64/0.71; PA 0.64; PB 0.61; elytra 1.83/1.03. Habitus as illustrated ( Fig. 44 ). Dorsum grey to dull silver, with little or no iridescence, elytra with black spots. Legs brown, lateral margin of tibiae with row of spines. Head with frons medially very slightly tumid, with longitudinal punctate groove on each side of tumidity. Punctation on elytra ca. 2–3x that of pronotum. 5 th interstria raised, without usual callus. 9 th interstria more convex than others, overhanging 10 th interstria.

Pronotum slightly wider than long (ratio ca. 38/35), widest at anterior margin, narrowed at base, sides weakly sinuate, non-denticulate; anterior margin bisinuate; depressions moderately large, moderately deep, more densely punctate than almost impunctate reliefs.

Elytra with intervals 3, 5, 7, and 9 slightly raised, not costate; punctures large, spaces between strial punctures ca. 1xpd; apices very slightly acuminate, separately rounded in dorsal view, in lateral view outer margin without angulation.

Ventral characters: Mentum moderately coarsely and moderately densely punctate, with shallow median fovea; submentum narrow, with transverse groove from side to side, posterior margin carinate, emarginate.

Male genitalia ( Fig. 44 ) general characters: genitalia without parameres; basal piece very elongate, straight in dorsal/ventral views, arcuate in lateral view; distal piece elongate, straight in dorsal/ventral views and lateral view, very slightly widened at apex, with central concavity, without processes; length ratios of basal piece/distal piece ca. 57/25.

Etymology. Named in reference to the very long male genitalia.

Figures

FIGURE 1. Dorsal habitus of Hydrochus species in study area.

FIGURE 70. Pictorial aid to species groups of Hydrochus from Bolivia, Brazil and Paraguay, using male genitalia. Not to same scale.

FIGURES 44–45. Habitus and male genitalia of holotypes. 44. Hydrochus longissimus n. sp. 45. Hydrochus casuarius n. sp.

FIGURES 57–58. Geographical distributions. 57. Endemics and near endemics. 58. H. bituberculatus.