Hydrochus liquidus, 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 : 29

Hydrochus liquidus , new species

Figs. 3 , 38 , 55

Type Material. Holotype (male): “ BRAZIL: Bahia, Piatã, Córrego na trilha para a casa do Agnaldo , Serra da Tromba , (13°16’9’’S, 41°46’18’’), 5.viii.2005 // stream, leg. Hamada, N., Pepinelli, M. Landeiro, V.L.” ( INPA) . Paratype: Same data as holotype (1 female INPA) .

Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.50 mm), the black dorsum, the elytral odd numbered interstriae subcostate to costate, the smooth rounded pronotal reliefs, the deep and coarsely densely punctate pronotal depressions, and the male genitalia ( Fig. 38 ; described below). Reliable determinations of similarly sized black specimens with costate elytra will require dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.50/1.02; head width 0.66; pronotum l/w 0.57/0.67; PA 0.67; PB 0.50; elytra 1.66/1.02. Habitus as illustrated ( Fig. 38 ). Body size moderate (ca. 2.50 mm). Dorsum black, with very slight or no iridescence, elytra without black spots. Legs brown, with tibiofemoral joints darker. Punctation on elytra ca. 3–5x that of pronotum. Elytra interstriae ca. 0.5x strial puncture diameter; odd numbered interstriae subcostate to costate. Usual area of callus on 5 th not raised.

Pronotum slightly wider than long (ratio ca. 36/31), widest at anterior margin, narrowed at base, sides weakly sinuate, smooth to microdenticulate; anterior margin sinuate; depressions deep; pronotum coarsely densely punctate, more densely punctate in depressions than on reliefs. Lateral and anterior margins with row of short setae.

Elytra with spaces between strial punctures ca. 0.5x their diameter; apices conjointly rounded in dorsal view, in lateral view outer margin with slight angulation; lateral most row of punctures in groove.

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

Male genitalia ( Fig. 38 ) general characters: genitalia very narrow, elongate, length ca. 7x greatest width, basal piece shorter than parameres (ratio ca. 4/7); paramere tips extending very slightly beyond aedeagus tip, medial margins beyond aedeagus tip parallel, plsa absent; parameres in dorsal/ventral views very narrow; in lateral view parameres straight, very sharply pointed apically; aedeagus very narrow, wider apically and sub-basally than at midlength; basal piece in dorsal/ventral views widening very slightly from orifice to distal end, in lateral view very asymmetrical, constricted just before lobe-shaped orifice.

Dorsal surface: adtl near base, just distal to adbl; pdmm approximating alm; adbl moderately large, basal end transverse, width slightly less than agw.

Ventral surface: avtl not apparent; pvmm separation similar to pdmm, neither overlapping alm.

Etymology. Named in reference to the pronotal sculpture, with very smooth reliefs, which give the impression of being melted, flowing.

Figures

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

FIGURES 38–39. Habitus and male genitalia. 38. Hydrochus liquidus n. sp., holotype. 39. Hydrochus jenniferiduae Makhan.

FIGURES 55–56. Geographical distributions. 55. Endemics and near endemics. 56. H. bicarinatus and H. merkli.