Hydrochus ampliarmus, 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 : 16-17

Hydrochus ampliarmus , new species

Figs. 3 , 49 , 57 , 70

Type Material. Holotype (male): “ BRAZIL: Rondonia, Machadinho d’Oeste, Balneário São José (-9.44573 - 61.98332), 103 m.; 9.vii.2018, leg. Short, margins of various places on river, BR18-0709-01A” ( INPA) . Paratype: Same data as holotype (1 SEMC) .

Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.28 mm), black color, the sculptured dorsum, with deep foveae, raised elytral intervals, small callus of 5 th elytral interstria, and the male genitalia ( Fig. 49 ; described below). Reliable differentiation from other similarly small sized black species with raised or costate elytra should include dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.28/0.91; head width 0.59; pronotum l/w 0.54/0.58; PA 0.58; PB 0.46; elytra 1.45/0.91. Habitus as illustrated ( Fig. 49 ). Dorsum black. Legs brown, lateral margin of tibiae with row of spines. Head with frons medially slightly tumid, with longitudinal punctate groove on each side of tumidity. Punctation on elytra ca. 3–5x that of pronotum. 5 th interstria raised, with usual callus, very small, low.

Pronotum slightly wider than long (ratio ca. 16/15), widest at anterior margin, strongly narrowed at base, sides weakly sinuate, non-denticulate; anterior margin bisinuate; lateral and anterior margins with row of moderately long setae; depressions large, deep, much more densely punctate than almost impunctate reliefs.

Elytra with intervals 3, 5, 7, and 9 very slightly raised, not costate; punctures large, spaces between strial punctures narrow walls to 1xpd, many punctures in off-set zig-zag pattern; apices acuminate, truncate apically in dorsal view, in lateral view outer margin without angulation.

Ventral characters: Mentum moderately coarsely and moderately densely punctate, with shallow median fovea. Submentum narrow, without foveae.

Male genitalia ( Fig. 49 ) general characters: genitalia without parameres, basal piece elongate, trisinuate in lateral view, in dorsal/ventral views straight, slightly widened at ca. midlength and distal 3/4; distal end produced in microreticulate lobe on dorsal surface, ventral apex produced in short beak-like shape.

Etymology. Named in reference to the width of the elytra at the humeral angles.

Remarks. The holotype has dorsal encrustations, which defied removal. This adversely affected the habitus images.

Figures

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

FIGURE 70. Pictorial aid to species groups of Hydrochus from Bolivia, Brazil and Paraguay, using male genitalia. Not to same scale.

FIGURES 48–49. Habitus and male genitalia of holotypes. 48. Hydrochus sculptissimus n. sp. 49. Hydrochus ampliarmus n. sp.

FIGURES 57–58. Geographical distributions. 57. Endemics and near endemics. 58. H. bituberculatus.