Hydrochus rectus, 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 : 33-34

Hydrochus rectus , new species

Figs. 2 , 23 , 59 , 71

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 (121): Brazil: Same data as holotype (77 NMNH) . Paraguay: Alto Parana, Estancia Dimas , (25°33’S, 55°13’W), 24–25.xi.2004, leg. U. Drechsel (21 NMW) ; same locality, 17–22.ii.2005, leg. U. Drechsel (17 NMW) ; Dep. Pte. Hayes, Puerto Galileo , (25°8’S, 57°50’W), 27– 29.viii.2005, leg. U. Drechsel (4 NMW) ; same locality, 1–3.xi.2005, leg. U. Drechsel (2 NMW) .

Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.17 mm), the pronotum with shallow impressions and rather dense punctuation, the pronotal shape, the brown to black color, and the male genitalia ( Fig. 23 ; described below). Differentiation from other similarly small sized species with similarly shaped pronotum will require dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.17/0.77; head width 0.55; pronotum l/w 0.50/0.54; PA 0.54; PB 0.46; elytra 1.36/0.77. Habitus as illustrated ( Fig. 23 ). Dorsum dark brown to black, with moderately strong purple iridescence on head, elytra without black spots. Legs testaceous, with tibiofemoral joints darker. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 0.5–1x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th not raised.

Pronotum slightly wider than long (ratio ca. 31/28), widest at anterior margin, narrowed at base, sides straight, with minute denticulations; anterior margin bisinuate; depressions very shallow; punctation dense, rather uniform over pronotum, but slightly denser in depressions.

Elytra with spaces between strial punctures narrow ridges to ca. 0.5x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with slight angulation; series 1–5 each terminating in larger, translucent punctures.

Ventral characters: Mentum with central depression; submentum with two foveae.

Male genitalia ( Fig. 23 ) general characters: genitalia very small, stout, length ca. 4x greatest width; parameres extending well beyond distal end of aedeagus, tips in dorsal/ventral views wide in proximal part, narrowing only slightly apically, apices blunt, medial margins straight, slightly diverging one from the other, in lateral view tips arcuate slightly toward ventrad, and markedly narrowing apically; basal piece long, longer than parameres (ratio ca. 7/5), sides slightly arcuate, tapering from distal end to base, constricted just before orifice, in lateral view arcuate, orifice markedly asymmetrical, with rim weakly sclerotized and characteristically shaped; aedeagus in dorsal/ventral views narrow, narrowing slightly from base to pointed apex, in lateral view much wider, sides arcuate, orifice markedly asymmetrical, hook-shaped.

Dorsal surface: adtl lacking; pdmm distinctively shaped, diverging one from the other at aedeagal apex, then widening to become contiguous, or slightly overlap one another, aedeagal apex visible in “window” created by pdmm shapes.

Ventral surface: pvmm more widely separated than pdmm, contiguous with or nearly so alm.

Etymology. Named in reference to the straight parameres, in dorsal/ventral views.

Figures

FIGURE 2. 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 22–23. Habitus and male genitalia of holotypes. 22. Hydrochus artus n. sp. 23. Hydrochus rectus n. sp.

FIGURES 59–60. Geographical distributions. 59. Endemics and near endemics. 60. H. formosus.