Hydrochus merkli Makhan, 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 : 46-47

Hydrochus merkli Makhan , new status

Figs. 2 , 11 , 56

H. merkli Makhan, 1993: 67

H. piroei Makhan, 1992 ; Oliva 1996; invalid synonymy by Oliva (1996) (see remarks)

Originally described from northern Argentina. New records from Argentina, Bolivia and Paraguay are given below.

Material examined (152): Argentina: Buenos Aires Province, Buenos Aires Parque , (34°36’13.32’’S, 58°22’53.76’’W), 1.i.1905, leg. no collector on label (1 MCZ) ; Monte Brown, W. Chascomus , (34°36’13.32’’S, 58°22’53.76’’W), 27–28.xi.1979, leg. C. M. & O. S. Flint (1 NMNH) ; Santiago del Estero, E. of Lapida, ponds along road Frias —Villa San Martin, elev. 200 m (28°22’55’’S, 64°31’36’’W), 24.ii.2004, leg. Beutel & Komarek (2 NMW) . Bolivia: Santa Cruz, 60 mi. N . Santa Cruz, Saavedra Exp. Sta. , December 27–30, 1959, Robert Cumming ” (7 NMNH) . Santa Cruz, Okinawa , 6.vi.1958, leg. E. Pinckert (6 CAS) ; Santa Cruz, 2.7 m S of San Jose , elev. 333 m (17°52’20’’S, 60°44’28’’W), 27.vi.1999, leg. K. B. Miller (1 SEMC) ; Santa Cruz, (17°48’S, 63°11’W), 11–12.v.1969, leg. P. & P. Spangler (1 NMNH) . Paraguay: Alto Parana, [no other locality data] (25°36’27.36’’S, 54°57’40.32’’W), 16.xi.1990, leg. Pena (1 NMW) ; Dep. Boqueron, Mistolar , (23°13’S, 61°41’W), 3–12.x.1997, leg. Drechsel (95 NMW) ; Dep. Pte. Hayes, Puerto Galileo , (25°8’S, 57°50’W), 27–29.viii.2005, leg. U. Drechsel (16 NMW) ; same locality, 1–3.xi.2005, leg. U. Drechsel (17 NMW) ; Paraquari, P.N. Yvycul, Arroya Mina , 640 ft., (25°37’34.32’’S, 57°9’7.56’’W), 26.vi.2006, leg. W.D. Shepard (WDS-A-1700) (1 SEMC) ; South of Sapucai, 550 ft., Arroyo Cuazu Cua , (25°39’41.76’’S, 56°57’37.8’’W), 21.vi.2006, leg. W.D. Shepard (WDS-A-1693) (3 SEMC) .

Differential Diagnosis. Among Bolivian species, recognized by the combination of moderate size (ca. 2.90 mm), the moderately shallow pronotal depressions, the moderately low and relatively impunctate pronotal reliefs, and the male genitalia ( Fig. 11 ; described below). This species has a generalized Hydrochus habitus; reliable determinations will require dissection of males.

Description. Size (length/width, mm): body (length to elytral apices) 2.90/1.00; head width 0.68; pronotum l/w 0.66/0.63; PA 0.61; PB 0.55; elytra 1.84/0.99. Habitus as illustrated ( Fig. 11 ). Dorsum grey, with moderately strong gold iridescence, elytra with black spots. Legs testaceous, with tibiofemoral joints slightly darker. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 1–2x strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Callus on usual area of 5 th interstria weakly raised, moderately long; 5 th also slightly widened and slightly raised over ca. 2 nd 1/5 of interstria length.

Pronotum length slightly less than width, widest at about anterior 1/3, narrowed at base, sides sinuate, smooth; anterior margin arcuate or very slightly bisinuate; depressions moderately deep, reliefs moderately raised, depressions more densely punctate than reliefs.

Elytra with spaces between strial punctures narrow ridges to ca. 0.5xpd; apices rather sharply conjointly round- ed in dorsal view, in lateral view outer margin with slight angulation; striae 1–3 each terminating in slightly larger, translucent puncture.

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

Male genitalia ( Fig. 11 ) general characters: genitalia narrow (l/w ratio ca. 47/8); paramere tips elongate, slightly widened, distal ends pointed, lateral margins straight from plsa to distal tip, medial margins of tips emarginate, distal end of tips extending slightly beyond aedeagus, in lateral view tips narrow, sharply pointed; aedeagus lanceolate in dorsal/ventral views, widest at ca. midlength, tapering to sharp distal end, with narrowly sclerotized lateral margins; basal piece slightly shorter than parameres (ratio ca. 23/25), tapering from distal end to slightly asymmetrical orifice, rim of orifice sclerotized.

Dorsal surface: adtl located at ca. midlength of aedeagus; pdmm narrowly overlapping alm over proximal 3/4, then slightly separated from alm where paramere tips begin; adbl moderately small, width equal to ca. ¼ width of genitalia at that level.

Ventral surface: pvmm very slightly overlapping alm at base; avtl at ca. proximal 1/6.

Remarks. Oliva (1996: 329) placed H. merkli Makhan, 1993 as a junior synonym of H. piroei Makhan, 1992 . I have examined the holotypes of both H. piroei (NBC) and H. merkli (NBC) , including the male genitalia, and find that they undoubtedly represent different species (see figures of H. piroei in Perkins, 2019c, and H. merkli herein). Consequently, the synonymy proposed by Oliva (1996), with H. merkli Makhan as a junior synonym of H. piroei Makhan , is invalid. The specimen imaged ( Fig. 11 ) has the following locality data: Bolivia: Santa Cruz, 60 mi. N. Santa Cruz, Saavedra Exp. Sta.

Figures

FIGURE 2. Dorsal habitus of Hydrochus species in study area.

FIGURES 10–11. Habitus and male genitalia of holotypes. 10. Hydrochus usualis n. sp. 11. Hydrochus merkli Makhan.

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