Hydrochus austrinus, 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 : 18

Hydrochus austrinus , new species

Figs. 3 , 16 , 59

Type Material. Holotype (male): Brazil: Rio Grande do Sul, “ Pelotas , 9 Jan. 1956, R. G. do Sul—Brasil, C. Biezanko leg.” ( NMNH) . Paratypes: Same data as holotype (5 NMNH) .

Differential Diagnosis. Among Brazilian species, recognized by the combination of moderate size (ca. 3.14 mm), the deep pronotal depressions, and the male genitalia ( Fig. 10 ; 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) 3.14/1.03; head width 0.71; pronotum l/w 0.66/0.69; PA 0.64; PB 0.61; elytra 2.04/1.03. Habitus as illustrated ( Fig. 16 ). Body size moderate (ca. 3.14 mm). Dorsum dark brown, with very slight or no iridescence, elytra with black spots. Body form narrow (l/w ratio ca. 41/24). Legs brown, 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 slightly more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th not raised.

Pronotum very slightly wider than long (ratio ca. 36/35), widest slightly behind anterior margin, narrowed at base, sides very weakly sinuate, smooth; anterior margin slightly bisinuate; depressions moderately deep, much more densely punctate than low 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. 16 ) general characters: genitalia elongate, length ca. 6x greatest width, basal piece and parameres ca. equal in length; paramere tips extending very slightly beyond aedeagus tip, medial margins beyond aedeagus tip parallel, plsa very small, lateral margins between plsa and apex straight; parameres in dorsal/ventral views very narrow over distal 2/3, straight; in lateral view parameres arcuate toward dorsad in distal 1/2, sharply pointed apically; aedeagus moderately wide, sides arcuate, agw at ca. midlength; basal piece in dorsal/ventral views nearly parallel-sided, in lateral view dorsal surface slightly more arcuate than ventral, orifice asymmetrical, margin sclerotized.

Dorsal surface: adtl at ca. midlength of aedeagus; pdmm widely separated; adbl moderately large, width slightly less than agw.

Ventral surface: avtl very near base, almost at alw; pvmm separation similar to pdmm, neither overlapping alm.

Etymology. Named in reference to the geographical distribution, at the southeastern extreme of Brazil.

Figures

FIGURE 3. Dorsal habitus of Hydrochus species in study area.

FIGURES 16–17. Habitus and male genitalia of holotypes. 16. Hydrochus austrinus n. sp. 17. Hydrochus diversus n. sp.

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

FIGURES 10–11. Habitus and male genitalia of holotypes. 10. Hydrochus usualis n. sp. 11. Hydrochus merkli Makhan.