Onychelmis minor sp. nov. urn:lsid:zoobank.org:act: 2705174E-0DB2-4D45-90A4-41665435AD62 Figs 3F, 6E, 10 C–D, 11E, 12A–B Differential diagnosis Onychelmis minor sp. nov. can be distinguished from all species of the genus by the combination of the following characters: 1) small size (CL: 1.01–1.07 mm); 2) pro- and mesofemora with tomentum reaching below apex (Fig. 6E); 3) humeri not well-developed; 4) prominent carina on sixth interval present; 5) elytral punctures absent; 6) apeX of aedeagus rounded with medial projection (Fig. 10 C–D). Etymology This species is named for being the smallest sized of all known Onychelmis species. Material examined Holotype ECUADOR • ♂; “Ecuador, Pastaza prov., Río Jantunpaccha, 01°26′30.6″ S, 77°52′25.5″ W, 1011 m a.s.l., 16. 8. 2013, stream ca. 5 m wide, slowly flowing, with mud and thin layer of gravel, Čiampor & Čiamporová-Zaťovičová lgt. ”; PUCE. Paratypes ECUADOR • 2 ♂♂, 2 ♀♀; same collection data as for holotype; PUCE / CCB. Other material ECUADOR • 1 ♀; same collection data as for holotype; CCB. Description Male BODY. Obovate (Fig. 3F); length 1.01–1.07 mm; width 0.52–0.54 mm; dorsum conveX, glabrous with sparse, light yellowish-brown setae. Hairy or scale-like tomentum distributed on following areas: genae, sides of prosternum, mesoventrite, metaventrite and abdomen, epipleura, medial and lateral portions on bases of femora. COLOUR. Head, pronotum, elytra, apices of femora, apical half of antennal segments 11 and apical third of tarsi 5 black; venter pale brown to brown with reddish tinge; antennae, coxae, trochanters, femora, tibiae, tarsi and tarsal claws pale brown. HEAD. Partly retractable into prothoraX, dorsally shiny. Antennae filiform, 11-segmented; pedicel about twice as long as scape; remaining segments about 4 times as long as scape and pedicel combined; segments 3–10 subrectangular, subequal in length; terminal segment longest, suboval, with pointed apex. Labrum with anterior margin almost straight; anterolateral angles broadly arcuate with numerous golden, recumbent hair-like setae; clypeus shorter and wider than labrum, about 3.5 times as wide as long, anterior margin slightly concave, anterolateral angles rounded; frontoclypeal suture almost straight. Eyes well developed, HW: 0.25–0.27 mm, ID: 0.15–0.16 mm, suboval in lateral view, protruding from head outline in dorsal view, circumocular surface raised. Frons between eyes convex. THORAX. Pronotum widest behind middle, PW: 0.34–0.35 mm, PL: 0.37–0.39 mm, surface shiny, with narrow reticulation along basal margin and posterolateral angles, with dense tiny punctures; sublateral carinae never well-developed, fine raised line indistinct; disc conveX, divided by broad, deep transverse impression on apical side of middle; two prescutellar foveae separated by raised line extending from base to apical discal half, connecting pronotal halves and merging into them; anterior margin arcuate; posterior margin bisinuate; sides of pronotum convex before and after transverse constriction; lateral margins narrowly rimmed; posterolateral angles orthogonal; anterolateral angles slightly produced. Hypomeron finely microreticulate, widest in middle. Prosternum moderately long in front of procoXae, with anterior margin concave; sides raised around procoxae, forming carinae, not reaching anterior margin, prosternal process long, moderately broad and with posterior margin broadly rounded. Mesoventrite coarse, short and wide, with deep triangular groove for reception of prosternal process; posterior margin around mesocoxae raised. Metaventrite slightly wider than long, shiny with setigerous punctures; disc convex with very shallow to indistinct, medial, triangular depression in posterior half; discrimen in basal ¾, very thin, almost indistinct; prebasal foveae absent. Elytra (EL: 0.64–0.69 mm, EW: 0.52–0.54 mm) convex, widest in about middle; disc convex, sides strongly declivous; surface shiny, with tiny punctures; elytral margin narrowly rimmed; humeri feebly developed; epipleuron tapering posteriorly. Prominent carina on siXth interval reaching ⅘ of elytron; strial punctures absent. Scutellum subovate, flat. Legs moderately long; femora clavate; tibiae longest. Protibiae with anterior cleaning fringe on apical ⅓; mesotibiae with two cleaning fringes – anterior on apical ⅕ and posterior on apical ⅓; metatibiae with posterior cleaning fringe on apical ⅓. Tarsi 5-segmented, first four segments each with one fine pale, recumbent seta, fifth segment slightly shorter than remaining segments combined; claws with a large subbasal and smaller basal teeth. ABDOMEN. With 5 ventrites. First ventrite with basal margin broadly rounded; fifth ventrite longest, apically setose, with posterior margin broadly arcuate. Aedeagus (Fig. 10 C–D) elongate. Penis without fibula; corona in apical half; in ventral view concave, constricted before rounded apeX with medial projection; in lateral view evenly narrowed from base to slightly curved apeX. Parameres absent. Phallobase slightly longer than penis, parallel-sided, in ventral view straight, curved in lateral view. Female EXternally similar to male, eXcept fifth ventrite more elongate. Biology Collected from slowly flowing stream ca 7 m wide with submerged vegetation, sparse larger stones and deep layer of fine gravel and sand (Fig. 11E). Distribution Known only from the type locality in Pastaza Province (Figs 11E, 12 A–B).

Published as part of Linský, Marek, Čiamporová-Zaťovičová, Zuzana & Čiampor, Fedor, 2021, A revision of Onychelmis Hinton, 1941 (Coleoptera: Elmidae), with description of new species, DNA barcoding and notes on the geography of the genus, pp. 1-35 in European Journal of Taxonomy 739 (1) on pages 26-29, DOI: 10.5852/ejt.2021.739.1263, http://zenodo.org/record/4600344