Hydrochus sculptissimus, 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 : 35-36

Hydrochus sculptissimus , new species

Figs. 1 , 48 , 55 , 70

Type Material. Holotype (male): “ BRAZIL: Para ; Rio Xingu Camp, (3°39’S, 52°22’W), Altamira (ca. 60km S.), 15 Oct. 1986, P. Spangler & O. Flint // Colln. #24 pond at 2nd palm grove on trail 1” ( NMNH).

Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.45 mm), black color, the highly sculptured dorsum, with deep foveae, costate elytral interseries, and abruptly raised, nipplelike, callus of 5 th elytral interstria, and the male genitalia ( Fig. 48 ; described below). Reliable differentiation from other similarly small sized black species with costate elytra should include dissection of males.

Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.45/1.02; head width 0.62; pronotum l/w 0.65/0.65; PA 0.65; PB 0.46; elytra 1.51/1.02. Habitus as illustrated ( Fig. 48 ). Dorsum black, except testaceous callus of 5 th interstria; very slight iridescence in depressions. Legs brown, lateral margin of tibiae with row of spines. Head with frons medially tumid, with longitudinal punctate groove on each side of tumidity. Punctation on elytra ca. 3–5x that of pronotum. Callus on 5 th small, round, high, very abruptly raised, with short setae.

Pronotum slightly wider than long (ratio ca. 9/8), widest slightly behind anterior margin, strongly narrowed at base, sides weakly sinuate, non-denticulate; anterior margin bisinuate; lateral and anterior margins with row of moderately long setae; depressions large, deep, much more densely punctate than almost impunctate rather sharp reliefs.

Elytra with sutural and intervals 3, 5, 7, and 9 costate; costa of 7 th interval interrupted in midlength, other costae complete; punctures very large, spaces between strial punctures narrow walls to ca. 0.5x their diameter, many punctures in off-set pattern; apices acuminate, rather sharply separately rounded in dorsal view, in lateral view outer margin without angulation.

Ventral characters: Mentum punctate, with central depression; submentum setose, without foveae.

Male genitalia ( Fig. 48 ) general characters: genitalia without parameres, basal piece elongate, trisinuate in lateral view, in dorsal/ventral views straight, slightly widened at ca. midlength and at distal 3/4; distal end with concavity on dorsal surface, minute bifurcate process in concavity.

Etymology. Named in reference to the very highly sculptured dorsum.

Figures

FIGURE 1. Dorsal habitus of Hydrochus species in study area.

FIGURE 70. Pictorial aid to species groups of Hydrochus from Bolivia, Brazil and Paraguay, using male genitalia. Not to same scale.

FIGURES 48–49. Habitus and male genitalia of holotypes. 48. Hydrochus sculptissimus n. sp. 49. Hydrochus ampliarmus n. sp.

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