Hydrochus diffusus, 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 : 23-24

Hydrochus diffusus , new species

Figs. 2 , 27 , 59 , 71

Type Material. Holotype (male): “ BRAZIL: Goias, 7km NE Paraiso , 1100m, 3–4 Oct. 1985, Scott E. Miller ” ( NMNH).

Differential Diagnosis. Among Brazilian species, recognized by the combination of moderately large size (ca. 4.26 mm), the moderately deep pronotal depressions, the rather uniform pronotal punctation, the elytra with small round widely separated black spots, and the male genitalia ( Fig. 27 ; described below). This species has a generalized Hydrochus habitus; reliable determinations will require dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 4.26/1.44; head width 0.94; pronotum l/w 0.90/0.98; PA 0.94; PB 0.82; elytra 2.80/1.44. Habitus as illustrated ( Fig. 27 ). Body size large (ca. 4.26 mm). Dorsum grey to reddish grey, without iridescence, elytra with small round widely separated black spots. Legs testaceous, with tibiofemoral joints darker. Punctation on elytra ca. 2x that of pronotum. Elytra interstriae ca. 2x strial puncture diameter. Interstria 9 th slightly more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th absent.

Pronotum slightly wider than long (ratio ca. 27/23), widest at anterior margin, narrowed at base, sides very weakly sinuate, smooth; anterior margin slightly bisinuate; lateral and anterior margins with row of short setae; depressions shallow to moderately deep; punctation rather uniform over pronotum.

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

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

Male genitalia ( Fig. 27 ) general characters: genitalia moderately stout, length ca. 3.8x greatest width, basal piece longer than parameres (ratio ca. 5/4); paramere tips and aedeagus tip at same level, paramere tips arcing toward midline, tips almost meeting, plsa absent, lateral margins of tips strongly arcuate; in lateral view parameres wide basally, tapering to rounded apex; aedeagus very wide in both dorsal/ventral and lateral views, oval, laterally heavily sclerotized, medial margins of sclerotized part together forming deep V-shape, agw at ca. midlength; basal piece in dorsal/ventral views tapering from distal end to base, in lateral view also tapering toward base, and arcuate, greatest width in dorsal/ventral views slightly greater than lateral width, orifice large, asymmetrical.

Dorsal surface: adtl subapical; pdmm approximating alm; adbl small, triangular.

Ventral surface: avtl not apparent; pvmm similar to pdmm in distal ½, in proximal ½ widely overlapping aedeagus, near base pvmm narrowly separated.

Etymology. Named in reference to the widely spaced black dots on the elytra.

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 26–27. Habitus and male genitalia of holotypes. 26. Hydrochus robustus n. sp. 27. Hydrochus diffusus n. sp.

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