Hydrochus argutulus, 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 : 17

Hydrochus argutulus , new species

Figs. 2 , 40 , 67 , 70

Type Material. Holotype (male): “ BOLIVIA: Beni Prov., VII, 10–19, 1960. B. Malkin leg. // Chacobo Indian Village on Rio Benicito , (12°20’S, 66°’W) // swept from air just before rain by lamp—p. m.” ( NMNH).

Differential Diagnosis. Among Bolivian species, recognized by the combination of very small size (ca. 1.95 mm), the light brown to reddish brown dorsum without black spots, the elytral interstriae narrow ridges, on disc often with zig-zag pattern due to large, alternately spaced punctures, the shallow pronotal depressions, the pronotal shape, and the male genitalia ( Fig. 40 ; described below). Differentiation from other similarly small sized species with similarly shaped pronotum and color should include dissection of males. This species is a member of the H. argutus species group (map, Fig. 67 ).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 1.95/0.78; head width 0.53; pronotum l/w 0.50/0.49; PA 0.47; PB 0.43; elytra 1.27 /0.78. Habitus as illustrated ( Fig. 40 ). Body size small (ca. 1.95 mm). Dorsum light brown to reddish brown, with very slight iridescence (holotype is teneral), elytra without black spots. Legs testaceous, with tibiofemoral joints darker. Punctation on elytra deep and large, ca. 1–2x that of pronotum. Elytra interstriae narrow ridges to ca. 1x strial puncture diameter, on disc often with zig-zag pattern due to large, alternately spaced punctures. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th not raised.

Pronotum length and width ca. equal, widest at anterior margin, narrowed at base, sides weakly arcuate, denticulate, each denticle with short arcuate seta; anterior margin arcuate; depressions shallow on disc, deeper laterally, densely coarsely punctate; reliefs very narrow between median and lateral foveae.

Elytra transversely quite convex, spaces between strial punctures narrow ridges; suture raised, especially at summit of posterior declivity; apices slightly widened, with submarginal groove having large translucent punctures.

Ventral characters: Mentum coarsely punctate, with median fovea. Submentum with deep transverse concavity.

Male genitalia ( Fig. 40 ) general characters: paramere tips appearing sagittate, but only in lateral view; in dorsal/ ventral views tips have contiguous medial margins, which extend beyond distal end of aedeagus; parameres slightly longer than basal piece (ratio ca. 15/12); basal proximal 1/2 strongly arcuate ventrad, enlarged at orifice.

Dorsal surface: adtl and adbl lacking; pdmm slightly overlapping alm.

Ventral surface: pvmm closer to one another than are pdmm.

Etymology. Named in reference to the small size, and the relationship with H. argutus .

Figures

FIGURE 2. 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 40–41. Habitus and male genitalia. 40. Hydrochus argutulus n. sp., holotype. 41. Hydrochus richteri Bruch.

FIGURES 67–68. Geographical distributions. 67. H. argutus species group. 68. H. cracentis.