Hydrochus purpureus Knisch

Perkins, Philip D., 2019, Taxonomy of Venezuelan water beetles in the genus Hydrochus Leach, 1817, and an analysis of male genitalia morphology (Coleoptera: Hydrochidae), Zootaxa 4708 (1), pp. 1-59 : 53-55

Hydrochus purpureus Knisch

Figs. 1 , 30

Hydrochous purpureus Knisch 1920: 57

Material examined: Venezuela: “ Bolivar: El Dorado (65 km S), 1 Nov. 1982, John L. Hellman ” (46 NMNH) .

Differential Diagnosis. Among Venezuelan species, differentiated from all, except other members of the collaris group ( H. collaris and H. conjunctus ), by the deep cervical groove behind the eyes. H. purpureus is slightly larger than the other two species (ca. 3.50 vs. 3.33 and 3.44 mm), and the pronotum has shallower depressions, lower reliefs, and generally more uniformly spaced punctation. Reliable determinations of members of these three species will require dissection of males. Male genitalia of H. purpureus ( Fig. 30 ) are described below; among differences from the other two species compared, the male genitalia have the aedeagus markedly tapering distally, and the greatest width of the aedeagus is proximal to midlength; the aedeagus always has an internal sclerotization that is slightly arcuate, in dorsal view going from the left side to the right side of the aedeagus. The internal sclerotizations of H. collaris and H. conjunctus are midlongitudinal, not arcuate.

Description. Habitus as illustrated ( Fig. 30 ). Size: holotype (length/width, mm): body (length to elytral apices) 3.50/1.30; head width 0.85; pronotum l/w 0.83/0.75; PA 0.75; PB 0.63; elytra 2.13/1.30. Body size moderate (ca. 2.69–3.77 mm). Dorsum grey, with slight iridescence, elytra with black spots. Legs testaceous to brown, with tibiofemoral joints darker. Punctation on elytra ca. 2x that of pronotum. Elytra interstriae ca. 2x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th well raised, rather elongate.

Head with deep curving cervical groove from side to side behind eyes, groove punctate, cervical area behind groove impunctate, shining, with low, closely set longitudinal raised lines.

Pronotum longer than wide (as ca. 83/75), widest at anterior margin, narrowed at base, sides slightly sinuate, smooth; anterior margin markedly arcuate, fitting into cervical groove; depressions shallow, if present, only slightly more densely punctate than very 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 distinct angulation, impunctate area of apices rather large.

Ventral characters: Mentum densely, moderately coarsely punctate, with shallow median fovea. Submentum with two deep foveae, posterior margin markedly arcuate.

Male genitalia ( Fig. 30 ) general characters: genitalia moderately slender; parameres expanded laterally apically in dorsal/ventral views, tips wider in dorsal/ventral views than lateral view, extending very slightly beyond distal end of aedeagus; basal piece shorter than parameres, lateral margins very slightly rounded, almost parallel, orifice strongly sclerotized, in lateral view hooking toward dorsad; aedeagus lanceolate, in lateral view much wider than parameres, lateral margins narrowly sclerotized, greatest width slightly before midlength, tapering apically, with slightly arcuate internal sclerotization, especially visible in dorsal/ventral views.

Dorsal surface: adtl lacking; pdmm approximating alm; adbl large.

Ventral surface: pvmm basally very slightly overlapping alm.

Figures

FIGURE 1. Dorsal habitus of Hydrochus species.

FIGURE 30. Hydrochus purpureus Knisch, habitus and male genitalia of non-type.