Taxonomy of Central American water beetles in the genus Hydrochus Leach, 1817 (Coleoptera: Hydrochidae) Author Perkins, Philip D. text Zootaxa 2021 2021-05-21 4974 3 459 503 journal article 6214 10.11646/zootaxa.4974.3.2 5b4eaeb3-5722-4021-84ad-125ccd80855f 1175-5326 4777839 1BD6220B-7540-4A12-B3D2-5EDC1A3B7DD8 Hydrochus argutoides , new species Figs. 2 , 4 , 38 Type material. Holotype (male): “ COSTA RICA : Guanacaste Prv., Rio Animas @ Rt. 4; 210 m elv, detrital pools & backwater, 13.i.2004 , AS-04-040, A.E.Z. Short & D. J. Lebbin ” ( SEMC ). Differential diagnosis. Among Central American species, recognized by the combination of small size (ca. 2.65 mm ), the pronotum with shallow, densely punctate depressions, the pronotal shape, with strongly denticulate lateral margins, the elytral disc with very large and deep punctures, the large punctures of the elytral apices, and the male genitalia ( Fig. 4 ; described below). Differentiation from other similarly small sized species with similarly shaped pronotum should include dissection of males. This species is a member of the H. argutus species group. Other members of the group include H. argutus Knisch ( Bolivia , southern Brazil , Paraguay ), H. argutissimus Perkins ( Venezuela ) , and an undescribed species from Bolivia (Perkins, in prep.). All members have the characteristic general shape of the male genitalia, which has a markedly arcuate basal piece, in lateral view. Description . Habitus as illustrated ( Fig. 4 ). Size: holotype (length/width, mm): body (length to elytral apices) 2.67 /1.01; head width 0.67; pronotum l/w 0.63/0.70; PA 0.66; PB 0.50; elytra 1.68 /1.01. Body size small (ca. 2.67 mm ). Dorsum dark brown to reddish brown, with slight iridescence, elytra without black spots. Punctation on elytra deep, ca. 2–4x that of pronotum. Elytra interstriae ca. 0.5–1× strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th not raised. Pronotum wider than long (ratio ca. 70/63), widest slightly behind anterior margin, markedly narrowed at base, sides straight, strongly denticulate; anterior margin bisinuate; depressions very shallow, densely punctate; reliefs very low, generally punctate. Elytra with punctures large and deep, spaces between strial punctures narrow ridges to ca. 0.5 puncture diameter; apices slightly widened, with submarginal groove having large translucent punctures and, apically, each elytron one large elongate puncture. Ventral characters: Mentum densely punctate, with median fovea. Submentum with two foveae. Male genitalia ( Fig. 4 ) general characters: paramere tips appearing sagittate, but only in lateral view ; in dorsal/ ventral views tips have medial margins separated, except meeting at distal end, tips extend well beyond distal end of aedeagus; basal piece long, in lateral view proximal 1/2 strongly arcuate ventrad, with terminal sclerotization. Dorsal surface: adtl and adbl lacking; pdmm slightly overlapping alm. Ventral surface: pvmm closer to one another than are pdmm. Etymology. Named in reference to the relationship with H. argutus .