Hydrochus trituberculatus, 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 : 37

Hydrochus trituberculatus , new species

Figs. 2 , 31 , 55

Type Material. Holotype (male): Brazil: Goias, “24 kil. E. Formoso, Go., Brazil May 23, 1956 F. S. Truxal ” ( NHMLAC).

Differential Diagnosis. Among Brazilian species, recognized by the combination of moderate size (ca. 3.48 mm), the dark grey to black color, the moderately deep pronotal depressions, the moderately low and relatively impunctate pronotal reliefs, the presence of three calluses on each elytron, and the male genitalia ( Fig. 31 ; described below). However, reliable determinations will require dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 3.48/1.02; head width 0.85; pronotum l/w 0.82/0.89; PA 0.84; PB 0.62; elytra 2.18/1.02. Habitus as illustrated ( Fig. 31 ). Body size moderate (ca. 3.48 mm). Dorsum grey to black, with slight to moderately strong iridescence, elytra with black spots. Legs testaceous, 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 more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th markedly raised, short, only ca. 3 punctures on each side; each elytron also with another callus on 5 th, anterior to usual callus, and another callus on 7 th interseries, ca. opposite middle of distance between two calluses on 5 th interseries.

Pronotum very slightly wider than long (ratio ca. 25/23), widest slightly behind anterior margin, narrowed at base, sides sinuate, smooth; anterior margin slightly bisinuate; depressions moderately deep, much more densely punctate than low reliefs between depressions, latter almost entirely impunctate.

Elytra with spaces between strial punctures ca. 1x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with angulation.

Ventral characters: Mentum densely punctate, with basomedian fovea; submentum very finely sparsely punctate, without foveae; metaventrite markedly tumid.

Male genitalia ( Fig. 31 ) general characters: genitalia very narrow, very elongate, length ca. 8x greatest width, wider in dorsal/ventral views than lateral (ratio ca. 2/1), basal piece as long as parameres; paramere tips not extending beyond aedeagus tip, tips arcuate toward midline, moderately sharply pointed, plsa absent; in lateral view parameres arcuate toward ventrad in distal 1/2, width ca. equal dorsal/ventral width, moderately sharply pointed apically; pseudoparameres very short, narrow, spike-like; aedeagus very narrow, almost parallel-sided for entire length, slightly widened apically and at base, the latter strongly sclerotized but not separate lobe; basal piece in dorsal/ventral views very narrow, sides very weakly arcuate if at all, length nearly four times width, in lateral view even narrower, very slightly arcuate, sides nearly parallel, orifice small, slightly asymmetrical.

Dorsal surface: adtl absent; pdmm widely separated, only contiguous with aedeagus at very base; adbl absent.

Ventral surface: avtl subapical, delimiting gonopore; pvmm separation similar to pdmm in distal ½, parameres wider in proximal ½, overlapping alm at base.

Etymology. Named in reference to the three prominent calluses on each elytron.

Figures

FIGURE 2. Dorsal habitus of Hydrochus species in study area.

FIGURES 30–31. Habitus and male genitalia of holotypes. 30. Hydrochus canalis n. sp. 31. Hydrochus trituberculatus n. sp.

FIGURES 55–56. Geographical distributions. 55. Endemics and near endemics. 56. H. bicarinatus and H. merkli.