Hydrochus compactus Perkins 2021, new species
Creators: name: Perkins, Philip D.
Publisher: name: Zenodo
Year: 2021
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Coleoptera
Hydrochidae
Hydrochus
Hydrochus compactus

description: Hydrochus compactus, new species   
Figs. 3, 34, 57  
 Type Material. Holotype (male): “ BRAZIL: Para; Rio Xingu Camp, (3°39’S, 52°22’W), Altamira (ca. 60km S.),, 11 Oct. 1986, P. Spangler & R. Crombie ” (NMNH).   
 Differential Diagnosis. Among Brazilian species, recognized by the combination of small size (ca. 2.10 mm), the compact body form, the black dorsum, the lack of a callus on the 5 th elytral interstria, and the male genitalia (Fig. 34; described below). Differentiation from other similarly small sized species with similarly shaped pronotum will require dissection of males.   
 Description. Size: holotype (length/width, mm): body (length to elytral apices) 2.10/0.82; head width 0.56; pronotum l/w 0.53/0.56; PA 0.54; PB 0.43; elytra 1.31/0.82. Habitus as illustrated (Fig. 34). Body size small (ca. 2.10 mm). Dorsum dark brown to black, with very weak iridescence, elytra without black spots. Legs testaceous, with tibiofemoral joints darker. Punctation on elytra ca. 2–3x that of pronotum. Elytra interstriae ca. 0.5x strial puncture diameter. Interstria 5 th raised, but lacking callus. Interstria 9 th more convex than others, overhanging 10 th interstria.   
Pronotum slightly wider than long (ratio ca. 32/28), widest at anterior margin, markedly narrowed at base, sides sinuate, with microdenticulations; anterior margin bisinuate; depressions shallow; punctation dense, coarse, denser in depressions than on reliefs.  
Elytra with spaces between strial punctures ca. 0.5x their diameter, or less; apices rather sharply conjointly rounded in dorsal view, in lateral view outer margin without angulation; submarginal row of punctures in common groove.  
Ventral characters: Mentum and submentum densely, moderately coarsely punctate; submentum without foveae.  
Male genitalia (Fig. 34) general characters: genitalia very narrow, elongate, length ca. 6.6x greatest width, basal piece shorter than parameres (ratio ca. 13/20); paramere tips extending well beyond aedeagus tip, medial margins beyond aedeagus tip diverging slightly one from the other, plsa absent, lateral margins of tips slightly emarginate; in lateral view parameres very narrow, slightly sinuate, sharply pointed apically; aedeagus narrow, sides arcuate, agw at ca. distal 2/3, adbl ca. same width; basal piece in dorsal/ventral views with slightly arcuate lateral margins, in lateral view arcuate, dorsal surface more arcuate than ventral, maximum width in dorsal/ventral views slightly greater than lateral width, orifice asymmetrical, margin sclerotized.  
Dorsal surface: adtl at ca. proximal 1/4; pdmm approximating alm, except underneath lateral margin of adbl; adbl large, width ca. equal to agw.  
Ventral surface: avtl at ca. distal 1/3; pvmm similar to pdmm.  
 Etymology. Named in reference to the compact body form.
description: Published as part of Perkins, Philip D., 2021, Taxonomy of water beetles in the genus Hydrochus Leach, 1817, from Bolivia, Brazil and Paraguay (Coleoptera: Hydrochidae), pp. 1-93 in Zootaxa 4994 (1) on pages 21-22, DOI: 10.11646/zootaxa.4994.1.1, http://zenodo.org/record/5043261