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 nayaritensis , new species Figs. 2 , 10 , 28 Type material. Holotype (male): Mexico : Nayarit , “ 25 km . S. Tepic , Nayarit MEX. IX-24-1953 , B. Malkin ” ( NMNH ). Differential diagnosis. Among Central American species, recognized by the combination of moderate size (ca. 3.68 mm ), the narrow body form, the rather uniformly densely punctate pronotum, and the male genitalia ( Fig. 10 ; described below). This species has a generalized Hydrochus habitus; reliable determinations will require dissection of males. The very narrow aedeagus, in dorsal/ventral views, could only be compared to that of H. brianbrowni . However, the shapes of the parameres, shape of the aedeagus in lateral view, shape of the adbl, and shape of the basal piece distinctly differ in the two species. The habitus of the two species also distinctly differ ( Figs. 9, 10 ). Description . Habitus as illustrated ( Fig. 10 ). Size: holotype (length/width, mm): body (length to elytral apices) 3.68/1.23; head width 0.83; pronotum l/w 0.75/0.85; PA 0.78; PB 0.73; elytra 2.33/1.23. Size moderately large (ca. 3.70 mm ), form narrow. Dorsum dark brown, with very little iridescence, elytra without black spots. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 1–1.5× strial puncture diameter. Interstria 9 th more convex than others, overhanging 10 th interstria. Usual area of callus on 5 th weakly raised, moderately elongate, ca. 6 punctures in row on each side. Pronotum slightly wider than long, widest slightly behind anterior margin, narrowed at base, sides weakly sinuate, smooth; anterior margin slightly bisinuate; rather uniformly densely punctate, except less dense on reliefs; depressions moderately deep Elytra with spaces between strial punctures ca. 1x their diameter; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin with moderate angulation. Ventral characters: Mentum coarsely moderately densely punctate, with median fovea. Submentum with two foveae. Legs testaceous, femora and tibiofemoral joints slightly darker than tibiae. Male genitalia ( Fig. 10 ) general characters: paramere tips very slender and pointed, wider in lateral view than in dorsal/ventral views, except for sharply pointed tips in lateral view; in dorsal/ventral views with medial margins at apex parallel or nearly so, then arcuate away from midline, without plsa; aedeagus in dorsal/ventral views very slender, slightly wider in distal ½, widest at adbl, apex pointed, lateral margins of aedeagus sclerotized; in lateral view sinuate, much wider in proximal ½, only slightly wider in distal 1/2; basal piece length equal to or only very slightly shorter than parameres, wider in proximal ½ then distal ½, in both dorsal/ventral and lateral views, orifice strongly sclerotized. Dorsal surface: pdmm widely separated, sinuate; adbl large; adtl as about distal 1/5; paramere tips without sclerotized ridge. Ventral surface: pvmm approximating lateral margin of aedeagus, except overlapping basally; avtl not apparent. Etymology. Named in reference to the geographical distribution.