Hydrochus tarsalis Chevrolat

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 : 13-14

Hydrochus tarsalis Chevrolat

Figs. 1 , 9

Hydrochus tarsalis Chevrolat 1863: 207

Material examined (28). Venezuela: Anzoategui: VZ10-0204-01A (1 SEMC) . Cojedes: VZ12-0122-01A (1 SEMC) . Guarico: VZ09-0108- 03X (1 SEMC) ; Calabozo (44 km S), Hato Masaguaral , 6 Mar 1986, PJSpangler, colln#30 (1 NMNH) ; San Fernando , II-12-1969, P. & P. Spangler (5 NMNH) ; Hato Masaguaral , 6 Mar 1986, PJSpangler & SBeaujon, colln#31 (1 NMNH) ; Calabozo (44 km S), Hato Masaguaral , 7 Mar 1986, PJSpangler & SBeaujon, colln#32 (2 NMNH) ; Calabozo (44 km S), Hato Masaguaral , 4 Mar 1986, large lake, PJSpangler, colln#22 (2 NMNH) . Zulia: VZ12-0127-01A (10 SEMC, MIZA, MALUZ) ; VZ12-0127 - 02 A (4 SEMC) .

Differential Diagnosis. Among Venezuelan species, recognized by the combination of large size (ca. 4.75–5.85 mm), the moderately coarse dorsal punctation, and the distinctive male genitalia ( Fig. 9 , and described below). Compared with other large Venezuelan species, it is not coarsely densely punctate as is H. pseudosecretus , and is generally smaller than H. ducalis , and slightly narrower (ca. 4.77 vs. 5.65 mm; TL/EW ca. 3.01 vs. 2.97). However, reliably separating specimens of H. tarsalis and H. ducalis will require dissection of males.

Description. Habitus as illustrated ( Fig. 9 ). Size of figured male (length/width, mm): body (length to elytral apices) 4.77 /1.55; head width 1.05; pronotum l/w 1.05 /1.09; PA 1.00; PB 0.91; elytra 3.05 /1.55. Large (Venezuelan specimens ca. 4.75–5.85 mm), moderately narrow, elongate. Dorsum dark dull grey with slight iridescence. Legs dark brown to black, with slight iridescence.

Head with punctures sparse, fine on clypeus, rather coarse on frons.

Pronotum slightly narrowed posteriorly, weakly convex, sparsely punctate, widest just behind anterior margin, narrowed at base (PA/PB ca. 1.00/0.91); pronotal disc not raised, punctures about the size of those on frons.

Elytra strongly broadened at 2/3 of length, behind this rather abruptly narrowed. Elytral striae shallow or not impressed, with round punctures distinctly larger than pronotal punctures, spaced by about their diameter. Inner interstriae wider than striae, flat on disk, weakly convex, if at all, on elytral declivity; outer interstriae convex. Callus on fifth interstria small; interstria 9 th convex, not or very slightly overhanging 10 th. Elytral apices broadened and rounded, lateral margin with slight angulation.

Ventral characters: Mentum coarsely punctate, with two small shallow foveae. Submentum with two foveae.

Male genitalia ( Fig. 9 ) general characters: paramere tips long, extending well beyond tip of aedeagus, slightly widened, with medial margins converging toward one another; basal piece much shorter than parameres, arcuate in lateral view, basal orifice rim strongly sclerotized and with lobate process.

Dorsal surface: adtl distinctive, and membranous part of aedeagus large; adbl characteristically shaped; medial margins of parameres overlaping lateral areas of aedeagus

Ventral surface: pvmm more widely separated from one another than are pdmm; membranous area as defined by avtl large, but smaller than dorsal counterpart.

Remarks. The specimen imaged ( Fig. 9 ) is from locality VZ12-0127-02A.

Figures

FIGURE 1. Dorsal habitus of Hydrochus species.

FIGURE 9. Hydrochus tarsalis Chevrolat, habitus and male genitalia.