Hydrochus dualis, Perkins, 2020

Perkins, Philip D., 2020, Taxonomy of Peruvian water beetles in the genus Hydrochus Leach, 1817 (Coleoptera: Hydrochidae), Zootaxa 4868 (1), pp. 61-89 : 72-73

Hydrochus dualis , new species

Figs. 1 , 8

Type Material. Holotype (male): “ Peru, S. A. Dec. 11–30, 1937, F. Woytkowski No. 3811 // Department Huanuco, Vic. Leonpampa, jungle, 800 m. a. s. l.” ( SEMC).

Differential Diagnosis. Among Peruvian species, recognized by the combination of large size (ca. 3.92 mm), the moderately deep pronotal depressions, the roundly raised, almost impunctate pronotal reliefs, the 5 th elytral interstria with two callosities, the usual posterior and another, smaller, slightly anterior, and the male genitalia ( Fig. 8 ; described below). Completely reliable determinations will include dissection of males.

Description. Habitus as illustrated ( Fig. 8 ). Size: holotype (length/width, mm): body (length to elytral apices) 3.92/1.54; head width 0.90; pronotum l/w 0.87/0.92; PA 0.82; PB 0.77; elytra 2.54/1.54. Body size large (ca. 3.92 mm). Dorsum grey with some black on head, with slight to moderate iridescence, elytra with black spots. Legs brown, with tibiofemoral joints darker. Punctation on elytra ca. 0.5–1x that of pronotum. Elytra interstriae ca. 1–3x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th markedly raised, moderately elongate, ca. 5 punctures in row on each side.

Pronotum very slightly wider than long, widest slightly behind anterior margin, narrowed at base, sides arcuate or very weakly sinuate, smooth; anterior margin slightly bisinuate; depressions moderately deep, more densely punctate than low reliefs between depressions, latter almost entirely impunctate; anteromedian depression less punctate than others.

Elytra with spaces between strial punctures ca. 1–2x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with moderate angulation; 3 rd and 4 th interstriae slightly raised immediately anterior to usual 5 th callosity; 5 th interstria with two callosities, the usual posterior and another, smaller, slightly anterior.

Ventral characters: Mentum densely punctate, with large, deep median fovea. Submentum with two foveae.

Male genitalia ( Fig. 8 ) general characters: genitalia very stout, wide in lateral view; paramere tips extending slightly beyond distal end of aedeagus, lateral margin between plsa and distal end emarginate, medial margin arcuate, in lateral view extreme end of tips upturned slightly; aedeagus lanceolate, greatest width distal to midlength, with alsm; pseudoparameres large, extending to level of distal end of aedeagus, pseudoparameres wider in lateral than dorsal/ventral views; basal piece shorter than parameres, orifice damaged during dissection.

Dorsal surface: adtl located proximal to midlength of aedeagus; pdmm sinuate, overlapping lateral margins of aedeagus only over proximal 1/4; adbl moderately large.

Ventral surface: avtl U-shaped, near basal 1/5 of aedeagus; pvmm not overlapping lateral margins of aedeagus; pseudoparameres enveloping most of basal ¼ of parameres.

Etymology. Named in reference to the two callosities on the 5 th interstria.

Remarks. The male genitalia of H. dualis are similar in some characters to that of H. ramcharani Makhan (figure of aedeagus given in Perkins, 2019c). Differences in the two species include: 1) in H. dualis the paramere tips, from plsa to distal end, are shorter and the lateral margin is entirely emarginate, whereas in H. ramcharani the tips are nearly twice as long and the lateral margin is straight except emarginate subapically; 2) in H. dualis the pseudoparameres are much wider in lateral view for the entire length, whereas in H. ramcharani the pseudoparameres are cylindrical beyond ca. the basal 1/3; and 3) in H. dualis the adtl is located more proximally than in H. ramcharani , hence the membranous dorsal part of the aedeagus is much larger in H. dualis .

Figures

FIGURE 1. Dorsal habitus of Hydrochus species.

FIGURE 8. Hydrochus dualis n. sp., habitus and male genitalia of holotype.