Hydrochus robustus, 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 : 35

Hydrochus robustus , new species

Figs. 2 , 26 , 59 , 71

Type Material. Holotype (male): “ BRAZIL: Bahia, 15 Km. E. Itabuna, VII-3-1969, P. & P. Spangler ” ( NMNH) . Paratypes: São Paulo, 10km SW Maricá , 11–12.x.1985, leg. Scott E. Miller (3 NMNH) .

Differential Diagnosis. Among Brazilian species, recognized by the combination of moderate size (ca. 3.33 mm), the dark grey to black dorsal color, without black spots, the moderately deep and densely punctate pronotal depressions, and the male genitalia ( Fig. 26 ; 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) 3.33/1.14; head width 0.79; pronotum l/w 0.76/0.78; PA 0.76; PB 0.67; elytra 2.08/1.14. Habitus as illustrated ( Fig. 26 ). Body size moderate (ca. 3.33 mm). Dorsum dark grey to black, with slight to moderately strong iridescence, elytra without 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 very weakly raised.

Pronotum very slightly wider than long (ratio ca. 43/39), widest slightly behind anterior margin, narrowed at base, sides sinuate, smooth; anterior margin very slightly bisinuate; depressions moderately deep, much more densely punctate than reliefs between depressions.

Elytra with spaces between strial punctures ca. 0.5–1x 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.

Male genitalia ( Fig. 26 ) general characters: genitalia stout, length ca. 4x greatest width, basal piece much shorter than parameres (ratio ca. 5/7); paramere tips and aedeagus tip at same level, paramere tips tapering and arcing slightly toward midline, plsa absent, lateral margins of tips arcuate; paramere widest part, in dorsal view, much narrower than aedeagus (ratio ca. 1/7); in lateral view parameres wide, sinuate, apex rounded; pseudoparameres ca. ½ length of parameres, with short spines; aedeagus very wide in both dorsal/ventral and lateral views, laterally very heavily sclerotized, medial margins of sclerotized part together forming deep V-shape, lateral margins of aedeagus arcuate, 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 greater than lateral width, orifice markedly asymmetrical, ventral margin slightly hook-shaped.

Dorsal surface: adtl near base; pdmm approximating alm; adbl absent.

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

Etymology. Named in reference to the very robust aedeagus.

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.