Hydrochus accinctus, 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 : 15

Hydrochus accinctus , new species

Figs. 1 , 24 , 53 , 70

Type Material. Holotype (male): “ BRAZIL: Amazonas ; Tapauá, -5.50298, -62.12392; 54 m, c. 240 km N Humaita on BR-319, 11.vii.2018; leg. Short, forest detrital pool, BR18-0712-01A” ( INPA).

Differential Diagnosis. A member of the H. spanglerorum species group, differentiated from the other members ( H. spanglerorum and H. colossus ) by the combination of slightly smaller size (ca. 4.23 mm), the very densely punctate dorsum, the very narrow elytral interstriae, and the male genitalia (described below, Fig. 24 ).

Members of the H. spanglerorum species group are recognized by the combination of the following characteristics: 1) large size, ca. 4.20–5.10; 2) head with very convex frons disc, with deep groove on each side of tumidity; 3) legs with densely, deeply punctate femora and tibiae; 4) 3 rd and 5 th elytral interstriae raised, costate to subcostate, throughout length, not additionally raised at usual area of callus; 5) male genitalia robust, lacking parameres and having articulated basal orifice. Three species are currently known, all in South America: H. accinctus n. sp., H. spanglerorum Perkins , and H. colossus n. sp. (habitus Fig. 1 ; map Fig. 53 ).

Description. Size: holotype (length/width, mm): body (length to elytral apices) 4.23/1.60; head width 0.94; pronotum l/w 1.00/1.04; PA 0.96; PB 0.83; elytra 2.75/1.60. Habitus as illustrated ( Fig. 24 ). Large (ca. 4.23 mm), elongate. Dorsum grey to very faint dull gold, with little or no iridescence. Legs dark brown except ventral surface of femora sometimes silver metallic with violet tint; all surfaces of femora densely coarsely punctate; tibiae with outer apical margin produced and bearing few short stout spines. Pronotum very densely, coarsely punctate. Elytral striae with deep round to slightly rectangular punctures; interstriae generally narrower than striae.

Head densely, coarsely punctate; frons markedly raised in middle, with deep groove on each side of timidity; frontoclypeal suture absent.

Pronotum wider than long (L/W as ca. 1.00/1.04), widest at about distal 2/3; anterior margin arcuate; narrowed at base; sides denticulate, sinuate; punctures on pronotum moderately sized, deep, very dense; depressions deep in anterior, central depression margined laterally with rather sharp ridge, very shallow in posterior.

Elytra with strial punctures very deep and ca. 2–3x those on pronotum; interstriae ca. 1x width of striae; 3 rd and 5 th interstriae raised, subcostate, throughout length, not additionally raised at usual area of callus; 9 th interstria raised and overhanging 10 th; apices truncate, with submarginal row of large, elongate punctures.

Ventral characters: Mentum very coarsely punctate, with large central depression; submentum with two deep, transverse foveae.

Male genitalia ( Fig. 24 ) general characters: genitalia large, strongly sclerotized, very asymmetrical; basal piece elongate, with articulated orifice.

Etymology. Named in reference to the very densely and deeply punctate 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 24–25. Habitus and male genitalia of holotypes. 24. Hydrochus accinctus n. sp. 25. Hydrochus amazonicus n. sp.

FIGURES 53–54. Geographical distributions. 53. H spanglerorum species group. 54. H collaris species group.