Hydrochus membraneus, Perkins, 2021

Perkins, Philip D., 2021, Taxonomy of water beetles in the genus Hydrochus Leach, 1817, from Bolivia, Brazil and Paraguay (Coleoptera: Hydrochidae), Zootaxa 4994 (1), pp. 1-93 : 30

Hydrochus membraneus , new species

Figs. 2 , 8 , 59

Type Material. Holotype (male): “ BRAZIL: Rio Grande do Sul, São Francisco de Paula , FLONA, lago portão de entrada, (29°23’31.48’’S, 50°22’54.43’’) // 2015 09 01, pond, leg. Benetti,C.J.; Pes, A.M.; Hamada, N. & Dantas, G.” ( INPA).

Differential Diagnosis. Among Brazilian species, recognized by the combination of moderate size (ca. 3.04 mm), the black dorsum, the comparatively small pronotum, the pronotal depressions moderately deep, much more densely punctate than the low reliefs between depressions, and the male genitalia ( Fig. 8 ; described below). This species has a generalized Hydrochus habitus; reliable determinations will require dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 3.04/1.04; head width 0.72; pronotum l/w 0.67/0.67; PA 0.63; PB 0.59; elytra 1.93/1.04. Habitus as illustrated ( Fig. 8 ). Body size moderate (ca. 3.04 mm). Dorsum black, with no iridescence, elytra without black spots. Legs brown, with tibiofemoral joints dark- er. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 1–1.5x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th very weakly raised, moderately elongate, ca. five punctures on each side.

Pronotum length and width ca. equal, widest at anterior margin, narrowed at base, sides very weakly sinuate, microdenticulate; anterior margin slightly bisinuate; depressions moderately deep, much more densely punctate than low reliefs between depressions.

Elytra with spaces between strial punctures narrow walls to ca. 0.5x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with slight angulation. Last punctures in first four striae larger than others, translucent.

Ventral characters: Mentum punctate, with central depression; submentum with two ill-defined foveae.

Male genitalia ( Fig. 8 ) general characters: genitalia elongate, length ca. 5x greatest width, basal piece shorter than parameres (ratio ca. 11/14); paramere tips extending beyond aedeagus tip, medial margins beyond aedeagus tip parallel, plsa small, lateral margins between plsa and apex straight, length unusually long; in lateral view paramere tips slightly arcuate toward dorsad, very sharply pointed apically; aedeagus wide, agw at ca. midlength, where aedeagus ca. 4x as wide as paramere, alm slightly emarginate between agw and distal end; basal piece in dorsal/ventral views nearly parallel-sided, in lateral view very slightly arcuate, orifice almost symmetrical, margin sclerotized.

Dorsal surface: adtl slightly proximal to midlength of aedeagus, membranous distal part very large; pdmm widely separated and approximating alm in distal ½, slightly overlapping alm in proximan 1/2; adbl moderately large, rounded laterally.

Ventral surface: avtl at ca. proximal 1/5; pvmm separation similar to pdmm, overlapping alm.

Etymology. Named in reference to the very large membranous area of the aedeagus.

Figures

FIGURE 2. Dorsal habitus of Hydrochus species in study area.

FIGURES 8–9. Habitus and male genitalia of holotypes. 8. Hydrochus membraneus n. sp. 9. Hydrochus irregularis n. sp.

FIGURES 59–60. Geographical distributions. 59. Endemics and near endemics. 60. H. formosus.