Hydrochus triangularis, 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 : 36-37

Hydrochus triangularis , new species

Figs. 3 , 7 , 57

Type Material. Holotype (male): Brazil: Mato Grosso, “ Rio Caraguata, M. Grosso, Brazil, IX-53, 21°48’S, 52°27’W, 400M alt., Fritz Plaumann leg.” ( NMNH). Paratypes (5): Bolivia: Beni Department, 7 km SW Trinidad, 14°52’12’’S, 64°57’32’’W, 163m, 18.vii.1998, leg. K. B. Miller ” (1 SEMC). Brazil: Mato Grosso, Corumba leg. F. Plaumann [no date] (1 NMNH). Paraguay: Central Dept. , 2 km N Luque, 23–24.vi.1969, leg. P. & P. Spangler (1 NMNH); Dep. Cordillera, San Bernadino, 23.vii.1998, leg. U. Drechsel (2 NMW).

Differential Diagnosis. Among species in the study area, recognized by the combination of moderate size (ca. 3.20 mm), the brown dorsum without black spots, the nearly parallel-sided body form, the pronotal depressions moderately deep, much more densely punctate than the low reliefs between depressions, and the male genitalia ( Fig. 7 ; described below). This species has a generalized Hydrochus habitus; reliable determinations will require dissection of males. The paramere tips are shaped similarly to those of H. distinctus ( Fig. 6 ); however, the other aspects of the male genitalia, and especially the dorsal habitus, differ in the two species.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 3.20/1.02; head width 0.75; pronotum l/w 0.69/0.70; PA 0.70; PB 0.59; elytra 2.06/1.02. Habitus as illustrated ( Fig. 7 ). Body size moderate (ca. 3.20 mm). Dorsum brown, with very slight to no iridescence, elytra without black spots. Legs testaceous, with tibiofemoral joints darker. Body form narrow (l/w ratio ca. 86/27). Punctation on elytra ca. 1–2x 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 moderately raised, moderately elongate, ca. 5 punctures on each side.

Pronotum very slightly wider than long (ratio ca. 19/18), widest at anterior margin, narrowed at base, sides slightly arcuate or very weakly sinuate, minutely denticulate; 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 separately rounded in dorsal view, in lateral view outer margin with slight angulation.

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

Male genitalia ( Fig. 7 ) general characters: genitalia large, elongate, length ca. 5x greatest width, basal piece very slightly shorter than parameres (ratio ca. 39/41); paramere tips extending slightly beyond aedeagus tip, medial margins beyond aedeagus tip parallel, plsa large, rounded, lateral margins between plsa and apex slightly arcuate; in lateral view parameres slightly arcuate, wide basally, tapering to sharply pointed apically; aedeagus wide, agw at ca. proximal 1/3, narrowing from there to apex and to base; basal piece in dorsal/ventral views parallel-sided, width in dorsal/ventral views and lateral view ca. equal, in lateral view very slightly arcuate, orifice slightly asymmetrical, margin sclerotized.

Dorsal surface: adtl at ca. distal 1/5; pdmm well separated in distal 1/5, remainder sinuate and overlapping alm; adbl very large, rounded laterally.

Ventral surface: avtl not apparent; pvmm more widely separated than pdmm, overlapping alm except for ca. distal 1/5.

Etymology. Named in reference to the triangular paramere tips.

Figures

FIGURE 3. Dorsal habitus of Hydrochus species in study area.

FIGURES 6–7. Habitus and male genitalia of holotypes. 6. Hydrochus distinctus n. sp. 7. Hydrochus triangularis n. sp.

FIGURES 57–58. Geographical distributions. 57. Endemics and near endemics. 58. H. bituberculatus.