Hydrochus irregularis, 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 : 28-29

Hydrochus irregularis , new species

Figs. 2 , 9 , 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) . Paratype: Same data as holotype (1 female INPA) .

Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.47 mm), the black dorsum, the elytral interstriae narrow walls in zigzag pattern, especially prominent on disc, the 5 th interstria with two calluses, the deep pronotal depressions, and the male genitalia ( Fig. 9 ; described below). Reliable determinations will also include dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.47/0.88; head width 0.58; pronotum l/w 0.53/0.59; PA 0.55; PB 0.51; elytra 1.58/0.88. Habitus as illustrated ( Fig. 9 ). Body size moderate (ca. 2.47 mm). Dorsum black, with slight to moderately strong iridescence, elytra without black spots. Legs brown, with tibiofemoral joints darker. Punctation on elytra ca. 3–6x that of pronotum. Elytra interstriae narrow walls in zigzag pattern, especially prominent on disc. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th weakly raised, moderately elongate, ca. five punctures on each side; 5 th also with low callus anterior to usual callus.

Pronotum very slightly wider than long (ratio ca. 32/29), widest slightly behind anterior margin, narrowed at base, sides slightly arcuate, smooth; anterior margin slightly bisinuate; depressions deep, much more densely punctate than low reliefs between depressions, some punctures confluent.

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 very slight angulation. Last punctures in first four striae larger than others, translucent.

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

Male genitalia ( Fig. 9 ) general characters: genitalia elongate, length ca. 5x greatest width, basal piece shorter than parameres (ratio ca. 19/21); paramere tips extending very slightly beyond aedeagus tip, medial margins beyond aedeagus tip parallel or nearly so, paramere tips tapering, plsa very small, lateral margins of tips between plsa and apex straight; in lateral view parameres straight, tapering to pointed apex, tips very slightly arcing dorsad; aedeagus moderately wide, distally tapering to sharp apex, sides weakly arcuate, agw at ca. proximal 1/3; basal piece in dorsal/ventral views tapering from distal end to base, in lateral view also tapering toward base, greatest width in dorsal/ventral views slightly greater than lateral width, orifice asymmetrical.

Dorsal surface: adtl at ca. distal 2/3; pdmm sinuate, widely separated over distal 1/3, overlapping alm over proximal 2/3; adbl large, width ca. slightly less than agw.

Ventral surface: avtl very near base; pvmm separation over proximal 2/3 much greater than pdmm; gp large. Etymology. Named in reference to the very irregular serial punctation of the elytra.

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.