Hydrochus curvus, 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 : 22-23

Hydrochus curvus , new species

Figs. 3 , 28 , 59 , 71

Type Material. Holotype (male): “ BRAZIL: Rio Grande do Sul, Bossoroca, Arroio Piratinim , (28°31’50.84’’S, 54°57’40.75’’W), 6.ix.2015 // river, on shores, leg. Benetti, C.J.; Pes, A.M.; Hamada, N. & Dantas, G.” ( INPA).

Differential Diagnosis. Among Brazilian species, recognized by the combination of very small size (ca. 2.13 mm), the brown dorsal color, the pronotal shape, the pronotum with very shallow impressions and rather uniform punctuation, the deep pronotal depressions, with punctation much denser than on reliefs, the rather steep elytral posterior declivity, and the male genitalia ( Fig. 29 ; 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) 2.13/0.79; head width 0.57; pronotum l/w 0.48/0.57; PA 0.55; PB 0.44; elytra 1.42/0.79. Habitus as illustrated ( Fig. 28 ). Body size small (ca. 2.13 mm). Dorsum brown, with little or no iridescence, elytra without black spots. Legs testaceous, with tibiofemoral joints darker. Punctation on elytra ca. 2x 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 very slightly raised.

Pronotum slightly wider than long (ratio ca. 31/27), widest at anterior margin, markedly narrowed at base, sides straight, denticulate; anterior margin bisinuate; depressions deep; punctation much denser in depressions than on reliefs.

Elytra with spaces between strial punctures ca. 2x their diameter; posterior declivity rather steep; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin without angulation.

Ventral characters: Mentum punctate, with central depression; submentum with small, median, circular pit.

Male genitalia ( Fig. 28 ) general characters: genitalia stout, length ca. 3.8x greatest width; basal piece orifice damaged, length vs. paramere length uncertain; paramere tips and aedeagus tip at same level, paramere tips arcing toward midline, tips meeting at midline, plsa absent, lateral margins of tips markedly arcuate; parameres wide in proximal 1/3, then abruptly narrowed for following ca. 1/3 of length, then widened in distal 1/3; in lateral view parameres wide, apex sharply rounded; pseudoparameres large, attaining distal 4/5 of parameres, at ca. midlength with cluster of large processes, medial margin distal to clusters with smaller processes; aedeagus in dorsal/ventral views ca. oval, much narrower in proximal 1/3, agw at ca. midlength; basal piece damaged, in dorsal/ventral views parallel-sided for most of length, orifice apparently large.

Dorsal surface: adtl indistinct, at ca. midlength; pdmm approximating alm; adbl small.

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

Etymology. Named in reference to the curvature of the lateral margins of the parameres.

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 28–29. Habitus and male genitalia. 28. Hydrochus curvus n. sp., holotype 29. Hydrochus radhakishunae Makhan.

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