Hydrochus alternatus, 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 : 63-66

Hydrochus alternatus , new species

Figs. 1 , 3

Type Material. Holotype (male): “ PERU: Madre de Dios; Rio Tambopata Res ; 30 air km SW Pto. Maldonado, 290 m, 16-20 xi 1979, J. B. Heppner, subtropical moist forest” ( NMNH) . Paratypes (6): PERU: Madre de Dios, Rio Tambopata Res ; 30 air km SW Pto. Maldonado, elev. 290 m (13°0’S, 69°33’W), 16–20.xi.1979, leg. J. B. Heppner (2 NMNH) ; same locality, 21–25.xi.1979, leg. J. B. Heppner (2 NMNH) ; same locality, 26–30.xi.1979, leg. J. B. Heppner (2 NMNH) .

Differential Diagnosis. Among Peruvian species, recognized by the combination of small size (ca. 2.08 mm), the narrow body form, the elytra with sutural interval and interstriae 3, 5, 7 and 9 costate, and the male genitalia ( Fig. 3 ; described below).

Description. Habitus as illustrated ( Fig. 3 ). Size: holotype (length/width, mm): body (length to elytral apices) 2.08/0.78; head width 0.54; pronotum l/w 0.47/0.50; PA 0.49; PB 0.43; elytra 1.42/0.78. Body size medium (ca. 2.08 mm). Dorsum black, with very slight if any iridescence, elytra without black spots. Legs dark brown. Punctation on elytra ca. 1–2x that of pronotum. Elytra interstriae ca. 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, widest slightly behind anterior margin, narrowed at base, sides weakly sinuate, denticulate; anterior margin slightly bisinuate; depressions deep, densely punctate.

Elytra with sutural interval and interstriae 3, 5, 7 and 9 costate; spaces between strial punctures narrow walls to ca. 0.5x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view with punctate submarginal groove, outer margin of apices without angulation.

Ventral characters: Mentum sparsely punctate, with median fovea. Submentum with two foveae.

Male genitalia ( Fig. 3 ) general characters: genitalia elongate, about four times as long as widest part in dorsal/ ventral views; parameres in distal ½ much narrower than aedeagus, in proximal ½ ca. as wide as aedeagus, paramere tips arcuate toward midline; pseudoparameres ca. ½ as long as parameres, wide proximally, narrowing distally and with spinose margins apically and medially; aedeagus widest subapically, becoming narrower from agw to basal area; basal piece shorter than parameres, distal ½ wider in dorsal/ventral views than lateral view, in dorsal/ventral views markedly narrowed at proximal end, in lateral view arcuate and only slightly narrower at proximal end than at distal end, orifice strongly sclerotized.

Dorsal surface: pdmm in proximal ½ slightly separated from alm, in distal ½ contiguous with, or very slightly overlapping alm; adbl and adtl lacking.

Ventral surface: pvmm contiguous with, or only very narrowly separated from alm at about midlength, proximal part narrowly separated from alm; pseudoparameres as described above.

Etymology. Named in reference to the costate odd-numbered elytral intervals.

Figures

FIGURE 1. Dorsal habitus of Hydrochus species.

FIGURE 3. Hydrochus alternatus n. sp., habitus and male genitalia of holotype.