Hydrochus artus, 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 : 17-18

Hydrochus artus , new species

Figs. 3 , 22 , 59 , 71

Type Material. Holotype (male): “ BRAZIL: Mato Grosso, Várzea Grande County, Cuiabá, Parque de Exposição , 28.v.1972, leg. R. Williams ” ( NMNH).

Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.15 mm), the pronotum with shallow impressions and rather dense punctuation, the pronotal shape, the brown to black color, the usual area of callus on 5 th interstria not raised, and the male genitalia ( Fig. 22 ; 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) 2.15/0.78; head width 0.55; pronotum l/w 0.48/0.54; PA 0.54; PB 0.45; elytra 1.32/0.78. Habitus as illustrated ( Fig. 22 ). Dorsum grey to silver or black, with weak iridescence, elytra without black spots. Legs testaceous to brown, 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. 30/26), widest at anterior margin, narrowed at base, sides straight or very slightly sinuate, smooth; anterior margin weakly bisinuate; depressions very shallow; punctation denser in depressions than on reliefs.

Elytra with spaces between strial punctures ca. 0.5x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin without angulation.

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

Male genitalia ( Fig. 22 ) general characters: genitalia small, elongate, length ca. 7x greatest width, basal piece slightly longer than parameres (ratio ca. 4/3); paramere tips extending well beyond aedeagus tip, medial margins beyond aedeagus tip diverging slightly one from the other, very slightly emarginate, plsa absent, lateral margins of tips very slightly arcuate; parameres with distinctive sclerotization; in lateral view parameres markedly tapering in distal 1/2, sharply pointed apically; aedeagus short, narrow in dorsal/ventral views, much wider, oval, in lateral view, in dorsal/ventral views agw at ca. distal 2/3; basal piece in dorsal/ventral views narrowing from distal end to just before orifice, then slightly widened, in lateral view arcuate, maximum width in dorsal/ventral views and lateral view ca. equal, orifice markedly asymmetrical, margin sclerotized.

Dorsal surface: adtl not apparent; pdmm markedly bisinuate, widely separated; adbl absent.

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

Etymology. Named in reference to the parameres, which apically narrow in both dorsal/ventral and lateral views.

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 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.