Taxonomy of Central American water beetles in the genus Hydrochus Leach, 1817 (Coleoptera: Hydrochidae) Perkins, Philip D. Zootaxa 2021 2021-05-21 4974 3 459 503 8Y4NX Perkins, 2021 Perkins 2021 [151,440,1255,1282] Insecta Hydrochidae Hydrochus Animalia Coleoptera 3 462 Arthropoda species aeruginosus sp. nov.   Figs. 1, 26, 29   Type material.  Holotype(male): “ MEXICO: Sonora, Rio Cuchujaqui,  7 mi.SE Alamos, ( 26°57’N, 108°51’W), black lite,  25-x-1972, E. M. Fisher” ( MCZ).   Paratypes(27):Same data as holotype (21 MCZ);  Mexico: Jalisco, Agua Caliente, unnamed stream, ( 20°23’N, 105°26’W),  15.i.2005, leg. W. D. Shepard(WDS-A-1624) (5 SEMC);  Nayarit, Acaponeta,  15.viii.1960, leg. E. S. Ross, D. C. Rentz, P. H. Arnaud Jr. (1 CAS).   Differential diagnosis.Among Central American species, recognized by the combination of small size (ca. 2.50 mm), the smooth dorsum with relatively sparse pronotal punctation, the lack of a callus on the 5 thelytral interstria, the greenish-blue dorsal color, and the male genitalia ( Fig. 26; described below). This species has a generalized  Hydrochushabitus; reliable determinations will require dissection of males. The male genitalia are readily recognized by the paramere tips which arc over the aedeagus, the latter being widest near the distal end, an unusual condition; also the shape of the basal piece orifice is unusual.   Description. Habitus as illustrated ( Fig. 3). Size: holotype(length/width, mm): body (length to elytral apices) 2.50/0.92; head width 0.65; pronotum l/w 0.58/0.65; PA 0.62; PB 0.52; elytra 1.63/0.92. Habitus as illustrated ( Fig. 26). Body size moderate (ca. 2.50 mm). Dorsum greenish blue, with strong to moderately strong iridescence, elytra without black spots. Punctation on elytra ca. 3–5x that of pronotum. Elytra interstriae ca. 0.5–1.5× strial puncture diameter. Interstria 9 thmore convex than others, overhanging 10 thinterstria. Usual area of callus on 5 thvery weakly raised, if at all. Pronotum slightly wider than long, widest slightly behind anterior margin, narrowed at base, sides arcuate, smooth; anterior margin slightly bisinuate; reliefs very sparsely punctate, depressions more densely punctate; depressions deep.   FIGURE 1.Dorsal habitus of Central American  Hydrochusspecies.   FIGURE 2.Dorsal habitus of Central American  Hydrochusspecies. Elytra with spaces between strial punctures narrow walls to ca. 1x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with very slight angulation. Ventral characters: Mentum coarsely moderately densely punctate, with large median fovea. Submentum with two large foveae. Legs dark brown, tibiofemoral joints slightly darker. Male genitalia ( Fig. 26) general characters: paramere tips only moderately slender, without plsa, with pmsm, slightly narrower in lateral view than in dorsal/ventral views, in dorsal/ventral views with distal tips meeting, medial margins arcuate around distal end of aedeagus; pseudoparameres attaining ca. midlength of parameres, tapering distally; aedeagus in dorsal/ventral views widest subapically, tapering from widest point to base; in lateral view wider, especially basally; lateral margins of aedeagus sclerotized; basal piece shorter than parameres, parallel-sided or nearly so in dorsal/ventral views, orifice sclerotized and produced in semi-cup shape. Dorsal surface: pdmm wide at adtl, then very narrowly separated; adbl small; adtl at about distal 1/5. Ventral surface: pvmm much more widely separated than pdmm, approximating lateral margin of aedeagus; avtl at ca. midlength of aedeagus.   Etymology.Named in reference to the greenish-blue dorsal color. 3128194380 1972-10-25 MCZ E. M. Fisher Mexico 26.95 Rio Cuchujaqui 1239 -108.85 3 462 1 Sonora holotype 3128194388 [662,1239,1400,1427] 1972-10-25 MCZ E. M. Fisher Mexico 26.95 Rio Cuchujaqui 1239 -108.85 3 462 1 Sonora paratype 3128194559 2005-01-15 SEMC W. D. Shepard Mexico 20.383333 Agua Caliente 1268 -105.433334 3 462 1 Mexico paratype 3128194515 [151,1134,1472,1499] 1960-08-15 CAS E. S. Ross & Ross, D. C & Rentz, P. H Mexico Acaponeta 3 462 1 Nayarit paratype