Hydrochus maximus, Perkins, 2020

Perkins, Philip D., 2020, Taxonomy of Ecuadorian water beetles in the genus Hydrochus Leach, 1817 (Coleoptera: Hydrochidae), Zootaxa 4790 (2), pp. 358-374 : 366-368

Hydrochus maximus , new species

Figs. 1 , 6

Type Material. Holotype (male): “ Ecuador: Past Tewaeno 20 May 1976 Cohen ” ( NMNH).

Differential Diagnosis. Among Ecuadorian species, recognized by the combination of large body size (6.00 mm long), the elongate elytra, the dull grey dorsum with numerous microsetae, the small and rather sparse pronotal punctuation, and the large male genitalia ( Fig. 6 ; described below). This is the largest known species of Ecuadorian Hydrochus ; the elytra are elongate, whereas the relative sizes of the head and pronotum are similar to that of other species (pronotum length/head width = 0.96).

Description. Habitus as illustrated ( Fig. 6 ). Size: holotype (length/width, mm): body (length to elytral apices) 6.00/2.05; head width 1.30; pronotum l/w 1.25 /1.25; PA 1.15; PB 1.10; elytra 3.90/2.05. Body size large (6.00 mm). Dorsum dull grey, with very weak if any iridescence, with numerous microsetae, elytra without black spots. Legs testaceous, with tibiofemoral joints darker. Punctation on clypeus denser than on frons, latter very sparse in midline, which has small timidity. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 2–3x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th moderately raised, moderately elongate.

Pronotum length and width equal, widest slightly behind anterior margin, narrowed at base, sides arcuate or very weakly sinuate, smooth; anterior margin weakly arcuate; depressions very shallow, reliefs between depressions very low, very sparsely punctate.

Elytra with spaces between strial punctures ca. 1–2x their diameter; apices conjointly rounded in dorsal view, in lateral view outer margin with moderate angulation.

Ventral characters: Mentum coarsely punctate, with median fovea. Submentum with two foveae. Legs testaceous, femora darker than tibiae.

Male genitalia ( Fig. 6 ) general characters: Genitalia very large, parameres and aedeagus much longer than basal piece, ca. 3x longer; in dorsal/ventral views aedeagus much wider than parameres, aedeagus rounded apically, with large internal sclerotization in proximal 1/2; parameres as long as aedeagus, rather flattened, much wider in lateral than dorsal/ventral views, distally tapering to narrow, rounded tip.

Dorsal surface: pdmm slightly overlapping lateral margin of aedeagus; adbl large; adtl indistinct, located at about distal 1/3, area distal to adtl with reticulate pattern (visible in microslide mount).

Ventral surface: pvmm approximating lateral margin of aedeagus; distal ½ of aedeagus with narrow alsm.

Etymology. Named in reference to the large size of the body and genitalia.

Remarks. The male genitalia in this species is very different in general structure and details from other large species of Neotropical Hydrochus , including H. tarsalis Chevrolet and H. ducalis Knisch (see Perkins 2019a), indicating that H. maximus is not closely related to those species.

Figures

FIGURE 1. Dorsal habitus of Hydrochus species.

FIGURE 6. Hydrochus maximus n. sp., habitus and male genitalia of holotype.