Hydrochus ducalis 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: 11-13

publication ID


publication LSID


persistent identifier


treatment provided by


scientific name

Hydrochus ducalis Knisch


Hydrochus ducalis Knisch  

Figs. 1 View FIGURE 1 , 6A View FIGURES 6 , 8 View FIGURE 8

Hydrochus ducalis Knisch 1921: 1   .

Material examined (28). Venezuela: Apure: AS-06-009 (8 SEMC, MIZA, MALUZ)   ; VZ09-0117 - 01X (1 SEMC)   . Bolivar: VZ09-0112-01B (1 SEMC)   ; 5 km E. Caicara , 11.VI.1996, at light, H. & A. Howden (2 CMN)   . Delta Amacuro: VZ10-0203-02A (2 SEMC)   . Guarico: Corozo Pando , (8 km N.), 17–18 June 1984, blacklight, F. W. Eiland & V. Linares (2 NMNH)   ; Corozo Pando , (8 km N.), 20–21 June 1984, blacklight, F. W. Eiland & V. Linares (3 NMNH)   ; 15 km S. Calabozo II-9-13-1969, collected in Lago de Los Patos , P. & P. Spangler (1 NMNH)   . Miranda: Guatopo NP, El Lucero , 28 km N Altagracia, 620m, 1–14.VI.1987, S&J Peck, UV light trap 87-17 (1 CMN)   . Monagas: VZ10-0202-01B (1 SEMC)   ; VZ10-0202 View Materials - 03 View Materials A (3 SEMC)   . Tachira: VZ09-0716-07A (1 SEMC)   ; VZ12-0126 View Materials - 02 View Materials A (2 SEMC)   .

Differential Diagnosis. Among Venezuelan species, recognized by the combination of large size (ca. 5.23–6.31 mm), the only moderately coarse dorsal punctation, and the distinctive male genitalia ( Figs. 6A View FIGURES 6 , 8 View FIGURE 8 ; describe below).

It is the largest Venezuelan Hydrochus   , and compared with other large species is not very coarsely densely punctate as is H. pseudosecretus   , and is generally larger than H. tarsalis   , and slightly broader (ca. 5.65 vs. 4.77 mm; TL/EW ca. 2.97 vs. 3.01). However, reliably separating specimens of H. tarsalis   and H. ducalis   will require dissection of males.

Description. Habitus as illustrated ( Fig. 8 View FIGURE 8 ). Size of imaged male (length/width, mm): body (length to elytral apices) body (length to elytral apices) 5.65 /1.90; head width 1.20; pronotum l/w 1.15 /1.25; PA 1.15; PB 1.10; elytra 3.60 /1.90. Large (ca. 5.23–6.31 mm, Venezuelan specimens), moderately narrow. Dorsum grey with slight iridescence, elytra with black spots. Legs dark brown to black. Dorsal punctation small to moderately large, moderately dense, distinctly larger on elytra than pronotum. Elytra interstriae slightly wider than strial punctures. Interstria 9 th more convex than others, overhanging 10 th interstria. Callus on 5 th interstria small and low, indistinct.

Pronotum slightly narrowed at base, sides arcuate or very weakly sinuate, smooth; depressions moderately small.

Elytral strial punctures ca. twice the size pronotal punctures, the spaces between them about half their diameter; apices rounded in dorsal view, in lateral view outer margin with slight angulation.

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

Male genitalia ( Figs. 6A View FIGURES 6 , 8 View FIGURE 8 ) general characters: paramere tips slender and pointed, with medial margins parallel or nearly so; basal piece slightly longer than parameres; aedeagus sinuate in dorsal and ventral views, slender in distal 2/3, widened basally ( Fig. 6A View FIGURES 6 ); in lateral view much wider, and produced in a prominent lobe (adm), what appears to be another lobe near the base is actually the dorsal margin of the paramere; lateral margins of aedeagus strongly sclerotized.

Dorsal surface: pdmm slightly sinuate; adbl very large, oval; adtl very near distal end.

Ventral surface: pvmm more strongly sinuate than pdmm, widened part accommodating widened part of aedeagus.

Remarks. The specimen imaged ( Fig. 8 View FIGURE 8 ) is from locality VZ10-0202-03A.


University of Kansas - Biodiversity Institute


Museo del Instituto de Zoologia Agricola Francisco Fernandez Yepez


Canadian Museum of Nature


Smithsonian Institution, National Museum of Natural History














Hydrochus ducalis Knisch

Perkins, Philip D. 2019

Hydrochus ducalis

Knisch, A. 1921: 1