Hydrochus diversus, 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 : 25-26

Hydrochus diversus , new species

Figs. 3 , 17 , 57 , 71

Type Material. Holotype (male): “ BRAZIL: Mato Grosso, Cuiaba Agri. Exp. Sta., IV.11.1972, W. H. Whitcomb ” ( NMNH).

Differential Diagnosis. Among Brazilian species, recognized by the combination of very small size (ca. 1.89 mm), the black dorsum, the elytral interstria 5 th not raised, and lacking callus, the shallow pronotal depressions, and the male genitalia ( Fig. 17 ; described below). Differentiation from other similarly small sized species with similarly shaped pronotum and elytral sculpture will require dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.89/0.76; head width 0.51; pronotum l/w 0.43/0.49; PA 0.47; PB 0.41; elytra 1.15/0.76. Habitus as illustrated ( Fig. 17 ). Body size small (ca. 1.89 mm). Dorsum dark brown to black, with very weak or no iridescence, elytra without black spots. Legs testaceous, with tibiofemoral joints darker. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 0.5x strial puncture diameter. Interstria 5 th not raised, and lacking callus. Interstria 9 th more convex than others, overhanging 10 th interstria.

Pronotum slightly wider than long (ratio ca. 27/23), widest at anterior margin, narrowed at base, sides very slightly sinuate, smooth; anterior margin arcuate; depressions shallow; punctation moderately dense, denser in depressions than on reliefs.

Elytra with spaces between strial punctures ca. 0.5x their diameter, or less; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin without angulation.

Ventral characters: Mentum punctate, with central depression; submentum with two foveae, small and widely separated.

Male genitalia ( Fig. 17 ) general characters: genitalia small, moderately stout, length ca. 5x greatest width, basal piece slightly longer than parameres (ratio ca. 6/5); paramere tips extending well beyond aedeagus tip, medial margins beyond aedeagus tip diverging slightly one from the other, slightly emarginate, plsa very small, lateral margins of tips sinuate; parameres with distinctive sclerotization; in lateral view parameres markedly tapering in distal 1/2, sharply pointed apically; aedeagus short, narrow, almost parallel-sided, slightly widened in proximal 1/2; basal piece in dorsal/ventral views narrowing from distal end to orifice, in lateral slightly arcuate, maximum width in dorsal/ventral views greater than lateral width, orifice markedly asymmetrical, margin sclerotized.

Dorsal surface: adtl not apparent; pdmm markedly bisinuate, widely separated; adbl absent.

Ventral surface: avtl not apparent; pvmm similar to pdmm.

Etymology. Named in reference to the marked difference in size of the parameres and the aedeagus.

Figures

FIGURE 3. Dorsal habitus of Hydrochus species in study area.

FIGURE 71. Pictorial aid to species groups of Hydrochus from Bolivia, Brazil and Paraguay, using male genitalia. Not to same scale.

FIGURES 16–17. Habitus and male genitalia of holotypes. 16. Hydrochus austrinus n. sp. 17. Hydrochus diversus n. sp.

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