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Potamophilus kelabitensis sp. nov., a new riffle beetle (Coleoptera, Elmidae) discovered in the Kelabit Highlands (northern Sarawak) and Sapulut environment (southern Sabah), is described. Illustrations of the habitus and diagnostic characters of the new species are presented. Differences from the type species P. acuminatus (Fabricius, 1792) from the Palaearctic region, based on DNA barcodes and morphological characters, are discussed. Selected morphological characters of all known species of Potamophilus from Vietnam, Myanmar, and Papua New Guinea are also compared with the new species. The systematic position of the genus relative to other sympatric genera of the subfamilies Larainae LeConte, 1861 and selected Elminae Curtis, 1830 belonging to three tribes is discussed based on phylogenetic trees inferred from the mitochondrial COI and nuclear ArgK as well as 18S rRNA gene sequences.

Potamophilus kelabitensis sp. nov. urn:lsid:zoobank.org:act: D801EBA4-C36A-4569-B495-7792B4B58F9D Figs 2–5 Type locality Malaysia, Sarawak, Miri district, Ramudu. Adults were collected at light in the Pa’Kelapang river environment in the Ramudu settlement (Fig. 5). Diagnosis Potamophilus kelabitensis sp. nov. is an elongated, parallel-sided, medium-sized (PEL: 5.3–7.3 mm), predominantly black species with reddish-brown antennal segments 1–4, distal portion of femora, trochanters, anterior face of mesofemora, and claws. The pronotum is about 1.5 × as wide as long, gradually expanded posteriad, widest in front of posterior margin, and deeply excised in hind angles. Pronotal sides are moderately arcuate, finely crenate, and explanate, on each side with conspicuous blunt tooth posteriorly; posterior angles are nearly rectangular. Pronotal surface bears dual punctuation. Large punctures are moderately larger than facets, nearly confluent or separated by distances up to 1.5× a puncture diameter, punctures appear to be denser laterally. Small punctures are intermixed within larger ones and are moderately larger than those on the head. Elytron with ten punctate striae and one accessory basal stria between the sutural and second stria. Strial punctures on the disc are more prominent than those on the pronotum, separated by one puncture diameter, punctures becoming smaller posteriorly; punctures in striae 6–10 are more prominent, appearing subquadrate and more closely arranged. Intervals are flat, finely punctured; sutural interval moderately raised; elytral apices are slightly deflected and not meeting at the suture, separated by a gap, narrowly rounded and not protruding. The aedeagus is trilobate, symmetrical; parameres in the apical portion are narrowed, flattened, abruptly bent ventrad, and less sclerotised; apices do not reach the apex of the penis. Differential diagnosis The new species differs from all other described species of Potamophilus by the following combination of external characters: – a relatively small size (separating it from P. feae); – distinctly crenate lateral margins of the pronotum (separating it from P. acuminatus, P. albertisii, P. feae, P. papuanus, and P. spinicollis); – deeply excised hind angles of the pronotum (separating it from P. albertisii); – lack of impression on the pronotal disc in front of the scutellum (separating it from P. acuminatus and P. spinicollis); – flat elytral intervals except the sutural one (separating it from P. acuminatus, P. feae, and P. spinicollis); – coarse strial punctures on the elytra (separating it from P. albertisii); – subquadrate and not rounded strial punctures in intervals 6–10 (separating it from P. acuminatus, P. feae, P. papuanus, and P. spinicollis); – evenly rounded elytral apices in both sexes (separating it from P. acuminatus, P. albertisii, P. feae, and P. papuanus); – the absence of a distinct, well-separated median tubercle on the meso- and metatibia in males (separating it from P. albertisii, P. feae, P. papuanus, and P. spinicollis). For the sake of convenience, brief diagnoses of the described species are given below. In P. acuminatus (PEL: ca 6.1–7.7 mm), the hind angles of the pronotum are deeply excised, pronotal sides are smooth, not crenate; pronotal disc with a wide, distinct depression in front of the scutellum. Strial punctures on the elytra are moderately coarse, sharply impressed, rounded, and separated by about their diameter. Elytra are long and narrow (ca 3.6–4.0 × as long as pronotum), with the first interval raised in the posterior 0.8 of its length, distinctly convex intervals 3 and 5, and other intervals flat to feebly convex. The apex of each elytron is produced, angulate in males while acuminate and more protruding with divergent apices in females. Meso- and metatibia are weakly sinuous; mesotibia in males is usually more strongly enlarged distally with an indistinct median tubercle. In P. albertisii (PEL: ca 6.8–7.1 mm), the hind angles of the pronotum are at most slightly emarginated, with the emargination at most half as wide as scutellum; pronotal sides are smooth, not crenate; pronotal disc is flat or at most indistinctly impressed in front of the scutellum. Strial punctures on the elytra are moderately fine to fine, conspicuously sharply impressed, elongate, and separated by about 1–2 × their length. The first elytral interval is raised, and the remaining intervals are flat or at most slightly convex, similarly as in P. kelabitensis sp. nov. The apex of each elytron is produced, angulate in males and acuminate in females, with subparallel apices. Meso- and metatibia are weakly sinuous, usually more strongly so and always with a distinct, acute median tubercle at the distal end of both tibiae in males. In P. feae (PEL: ca 9.5–10.4 mm), the hind angles of the pronotum are deeply excised; pronotal sides are smooth, not crenate; pronotal disc is at most indistinctly impressed in front of the scutellum. Strial punctures on the elytra are moderately coarse, more delicate on the declivity, moderately sharply impressed and rounded, separated by about 1–2 × their diameter; first and third interval in the posterior half are distinctly raised, other intervals at most feebly convex. The apex of each elytron is produced, more or less angulate, the angle acute (ca 60°), with an almost identical shape in both sexes. Mesotibia is weakly sinuous, and the distal end bears a stout median tubercle in males; metatibia is almost straight in both sexes. In P. papuanus (PEL: ca 5.4–5.9 mm), the hind angles of the pronotum are deeply excised; pronotal sides are smooth, not crenate; pronotal disc is evenly convex to flat in front of the scutellum. Pronotal disc is densely and finely punctate with the punctures smaller than the eye facets, i.e., the punctuation is finer than in P. kelabitensis sp. nov. Elytral intervals are more or less flat, and only the first interval is raised in about the posterior half; strial punctures are rounded, moderately large (slightly larger than eye facets), well and sharply impressed, separated by about 1–2 × their diameter. Elytral apices have an acute angle in males and are angulate to acuminate in females. Mesotibia and metatibia are distinctly curved/sinuate with a blunt tubercle on the mesal face of the distal part in males, nearly straight or only weakly sinuate in females. In P. spinicollis (PEL: ca 7.0 mm), the hind angles of the pronotum are deeply excised; pronotal sides are smooth to indistinctly and irregularly crenate, especially in the posterior half; pronotal disc with a distinct subtriangular depression in front of the scutellum. Elytral intervals are convex on the disc, with the first interval raised in the posterior 0.8 of its length. Strial punctures are rounded and conspicuously coarse, larger than those on the pronotum and much larger than eye facets, well and sharply impressed, separated by at most their diameter on the disc, smaller and sparser towards the lateral sides and posterior declivity. Male with the apex of each elytron separately rounded (female unknown) and with a rather prominent, pointed tubercle on the mesal face of the distal part of meso- and metatibia. Etymology The species is named after the Kelabit Highlands, an isolated highland plateau in the interior of the Sarawak State (Malaysia) and bordering the Kalimantan Province (Indonesia). Type material Holotype MALAYSIA • ♂; “ Malaysia, Sarawak, Miri distr., Ramudu, 26.06.2018, (15) 3°33′17.0″ N 115°29′38.5″ E 921 m a.s.l., Pa’Kelapang riv. env., J. Kodada & D. Selnekovič lgt., at light ”; CFDS. Paratypes MALAYSIA • 11 ♂♂, 7 ♀♀; same collection data as for holotype; CFDS, CKB • 1 ♀; “ Malaysia, Sarawak, Miri distr., Bario, 19.– 23.6.2018, Lian Labang Garden, at light, J. Kodada & D. Selnekovič lgt.”; CKB JK540 • 2 ♂♂, 2 ♀♀; “ Malaysia, Sabah, Batu Punggul Resort env., river in primary forest, 25.Vi. 1990 ”; NHMW. Measurements (all values in mm) PEL: ♂♂ 5.31–5.46 (5.39 ± 0.06, n = 11), ♀♀ 5.77–6.93 (6.18 ± 0.36, n = 7); PL: ♂♂ 1.31–1.36 (1.32 ± 0.03, n = 11), ♀♀ 1.46–1.51 (1.51 ± 0.07, n = 7); PW: ♂♂ 1.91–1.97 (1.97 ± 0.09, n = 11), ♀♀ 2.07–2.57 (2.24 ± 0.16, n = 7); EL: ♂♂ 4.09–4.19 (4.14 ± 0.04, n = 11), ♀♀ 4.39–5.30 (4.76 ± 0.28, n = 7); EW: ♂♂ 2.12–2.22 (2.18 ± 0.03, n = 11), ♀♀ 2.42–3.14 (2.61 ± 0.23, n = 7); HW: ♂♂ 1.21–1.26 (1.25 ± 0.03, n = 11), ♀♀ 1.31–1.51 (1.37 ± 0.06, n = 7); ID: ♂♂ 0.71–0.80 (0.76 ± 0.27, n = 11), ♀♀ 0.81–0.91 (0.84 ± 0.05, n = 7). Description Holotype The description of the holotype is completed by figures of the holo- and paratype specimens (Fig. 2). BODY (Fig. 2A). Elongated, about 2.5× as long as wide (PEL/EW), parallel-sided, and moderately convex. Length including head 5.90 mm, maximal width across elytra 2.1 mm. Overall colour black; antennal segments 1–4, ventral mouthparts, distal portion of femora, trochanters, anterior face of mesofemora, and claws reddish-brown. Vestiture consists of longer, more or less erect setae and short, strongly recumbent, hair-like setae. Longer setae acute, in narrow sockets; dorsal ones moderately dense, brownish. Ventral setae yellowish, denser on lateral portion of thorax, posterior and lateral portion of ventrites, mainly on ventrites 3–5 and on coxae and trochanters (Fig. 2C). Short setae in narrow sockets (micropunctures), moderately densely to densely arranged, especially ventrally very dense. HEAD (Fig. 2D). Moderately wider than long, large (HW: 1.2 mm), moderately declined dorsally, arched laterally and flattened ventrally; slightly retracted into prothorax; frontoclypeal suture finely marked. Labrum transverse, lateral angles rounded, anterior margin feebly emarginated in middle; very dense yellowish setae in close rows along anterior margin and laterally; surface finely punctured, with numerous longer setae. Anterior margin of clypeus straight, bordered by a row of longer setae, clypeus moderately shorter than labrum. Frons without sublateral depressions, surface densely punctured, puncture diameter slightly larger than a facet diameter, punctures separated by 0.5–1.5 × puncture diameter; interstices shiny, with micropunctures. Eyes large and strongly protuberant (ID: 0.7 mm), nearly circular in lateral view, without interfacetal setae, dorsally surrounded by long conspicuous setae. Antennal insertions exposed from above, close to eye margin; subantennal groove vaguely indicated only, shallow and short. Genae without anterolateral process, with numerous longer setae anteriorly. Gula as wide as long, not in the same plane with mentum, with cavity surrounded by dense hair-like setae; gular sutures straight; submentum short, transverse, densely punctured. Cervical sclerites large, wide and strongly sclerotised. Antenna 11-segmented, serrate, reaching slightly behind anterior margin of pronotum. Scape half as long as ID, moderately curved; posterior face flattened, lacking setae. Pedicel 0.5 × as long as scape, both with conspicuously long, hair-like sensilla; combined length of antennomeres 3–11 moderately longer than combined length of previous antennomeres.Antennomeres 6–10 transverse and more tightly aligned than previous antennomeres. Length/width of antennomeres 1–11 (in mm) as follows: 0.36/0.16: 0.18/0.99: 0.12/0.09: 0.06/0.08: 0.08/0.09: 0.81/0.09: 0.06/0.09: 0.06/0.09: 0.06/0.09: 0.06/0.09: 0.08/0.08. Maxillary palpus four-segmented, shorter than ID; terminal palpomere short, apically enlarged and truncate, with large sensory field; palpomeres 2 and 3 subequal in length, widened distally, with numerous moderately long hair-like sensilla. Mentum flat, short and wide, setose, with sides subparallel; palpigers strongly sclerotised, free, and unfused mesally. Labial palpus three-segmented, half as long as maxillary palpus; first segment short; second segment longer, with short and long hair-like sensilla around apical margin; third segment slightly longer than preceding, with apical sensory field similar to that on maxillary palpus. Ligula short and wide, more strongly sclerotised mesally than anterolaterally; anterior angles rounded, produced laterad. THORAX. Pronotum 1.47 × as broad as long, PW: 1.95 mm, PL: 1.30 mm, gradually expanded posteriad, widest in front of posterior angles and deeply excised in hind angles. Pronotal sides moderately arcuate, finely crenate and explanate, on each side with conspicuous blunt tooth (projection) posteriorly; posterior angles almost rectangular; anterior angles not protruding. Anterior margin straight, sides with collar-like thickening; posterior margin trisinuate. Disc moderately convex, with two small prescutellar foveae, strongly deflexed laterad and anteriad. Surface with dual punctuation; large punctures moderately larger than facets, nearly confluent or separated by distances up to 1.5 × puncture diameter, appear to be denser laterally. Small punctures moderately larger than those on head, intermixed within larger ones. Hypomeron with ventral outline trisinuate, deepest emargination at level of procoxae. Width of hypomeron subequal in middle third, moderately narrowed anteriad and posteriad; anterior depression for reception of antennal tip small. Prosternum in front of coxae very short, distinctly shorter than prosternal process, transverse and not concealing head in repose. Prosternal process about twice as long as wide, subtriangular, posterior half distinctly narrowed, sides raised; mesal portion with longitudinal keel. Procoxae transverse, countersunk; procoxal cavities open posteriorly, moderately widely separated; postcoxal projection absent. Mesoventrite moderately shorter than prosternal process, separated by sutures from surrounding sclerites, posterior angles more or less produced posteriad and overlapping metaventrite; mesoventrite divided by fine discrimen; groove for reception of prosternal process deep, present along entire length, posteriorly widened. Mesocoxae large and prominent, subglobular; mesally separated by distance twice as wide as procoxae. Scutellary shield (scutellum) small, subtriangular, as wide as long, sides arcuate. Metaventrite twice as long as mesoventrite; anterior edge of metaventrite not carinate between mesocoxal cavities, anterolateral portion flat; exposed portion of anepisternum 3 moderately wide and long. Metaventral disc convex on sides, with sizeable medial depression extending from anterior third to posterior margin and with small medial depression anteriorly; discrimen fine, present along entire length of metaventrite; metakatepisternal suture subtle, hardly visible; surface finely punctured. Metacoxae large, transverse, oblique, almost reaching elytra, separated from metaventrite by a suture, posteriorly excavate for reception of femora. Elytra 4.05 mm long (EL) and 2.15 mm wide (EW), subparallel-sided, moderately convex; each elytron with ten punctate striae and one accessory basal stria between sutural and second stria. Strial punctures on disc moderately larger than those on pronotum, separated by ca distance of puncture diameter, punctures becoming smaller posteriorly; punctures in striae 6–10 larger, appearing subquadrate and more closely arranged; intervals flat, finely punctured; sutural interval moderately raised. Humeri rounded and prominent; lateral margin moderately explanate, inflected at level of metacoxae; anterior margin smooth; elytral apices slightly deflected and not meeting at suture, separated by a gap, narrowly rounded and simple. Epipleura strongly inflected at the level of metacoxae, their width subequal along entire length, oblique and received in deep grooves on meso- and metathorax; posteriorly relatively tightly fitted to abdomen. Hind wing large, darkly pigmented, fully developed. Legs nearly as long as elytra; femoral pubescence short; tibial groove shallow, present on ca distal 0.66. Tibiae moderately longer than femora, slightly curved, nearly straight; pro- and metatibiae with dense short pubescence; mesotibia flattened and lacking dense pubescence, extended and slightly bent at apex with a trace of tubercle. Tarsi fivesegmented, ca half as long as tibiae (except claws), pro- and metatarsi densely pubescent; claws simple, similar in form and angle of inclination. ABDOMEN. Five strongly sclerotised ventrites present, all well separated by sutures; first three ventrites connate, remaining two separated by thin membrane, movable; ventrites moderately convex, shallowly depressed along midline; first ventrite not entirely divided by metacoxae, admedian carinae absent; lengths of ventrites 1–5 (in mm): 0.75: 0.50: 0.35: 0.30: 0.45. Intercoxal process wide, subtriangular, acute anteriorly; lateral margins moderately raised; fifth ventrite truncate posteriorly and shallowly emarginate in middle. Surface of ventrites finely punctured and densely setose; third and fourth ventrites bears conspicuous longer, narrowly spaced, flattened setae near posterior margin; numerous flattened setae also on central and apical portion of fifth ventrite. Male sternite VIII symmetrical, deeply emarginate posteriorly and with numerous dense, long setae; anterior median struts short and thin (Fig. 4D). Tergite VIII dark, well sclerotised, narrowly rounded posteriorly, with dual punctuation and setation. Male sternite IX asymmetrical, anterior median strut long; posterior portion well sclerotised, semitubular, surrounding phallobase; posterior edge shallowly emarginated (Fig. 4C). AEDEAGUS.Trilobate, symmetrical (Fig. 3A–B), ca 1.30 mm long; phallobase including anterior projection ca 0.7 × as long as parameres, nearly tubular, lateral portions sclerotised, ventral and dorsal portions membranous. Parameres individually articulated with phallobase, dorsally fused near base, ventrally free along whole length; parameres narrowed, flattened, abruptly bent and less sclerotised in apical portion (Fig. 3C), apices do not reach the apex of penis. Penis symmetrical, basal portion expanded ventrally nearly in the form of a ʻbellʼ; dorsal portion flattened with lateral sides explanate in basal 0.6 and further gradually narrowed apicad, thus penis nearly round in cross-section, with apex bent ventrad; ventral sac membranous without fibula, corona present. Female terminalia Posterior margin of female sternite VIII widely rounded; surface with numerous long, dense dark setae (Fig. 4E); anterior margin with robust, subtriangular median strut, the latter subequal in length to posterior portion of sternite. Tergite VIII wider and widely rounded posteriorly; punctuation and setation similar to that of ma

Elmomorphus brevicornis Sharp, 1888 Figs 4A–C, 5A, 6A, C, E, 7A–D, 8A–B, E–F, 9A–B, D, 10A Elmomorphus brevicornis Sharp, 1888: 243 (original description, type locality). Helichus “ 862 spec.?” Lewis 1879: 12 (first indication). Elmomorphus brevicornis – Zaitzev 1910: 19 (catalogue). — Kôno 1934: 125 (catalogue). — Bollow 1940: 59–62, figs 271–276 (description, Japanese records). — Chûjô & Satô 1964: 193. — Delève 1968: 151 (differential diagnosis). — Satô 1981: 53. — Jäch 1984: 314 (checklist). — Kodada & Jäch 2006: 442 (catalogue). — Hayashi & Shimada 2006: 129 (Japanese records, in Japanese). — Yoshioka 2007: 236, 242, fig. 17a (Japanese records, in Japanese); 2008: 224 (Japanese records, in Japanese). — Hayashi 2011: 93. — Kamezawa & Nomura 2013: 29 (Japanese records, in Japanese). — Jung & Bae 2014: 2–7, figs 2a–c, 3–5 (description, identification key, Korean records). — Kodada & Jäch 2016: 606 (catalogue). — Yoshitomi & Haga 2018: 341–342 (identification key). — Nakajima et al. 2020: 177, 322 (diagnosis, identification key, photographs of living specimens). non Elmomorphus brevicornis – Devi et al. 2016: 371–373 (misidentification, invalid lectotype designation)]. Type locality Kobe, Hyōgo Prefecture, southern Honshu, Japan. Material examined Syntypes JAPAN • 1♂ (Fig.4C);“Kobe 18.V.71 [handwritten]|Japan.G Lewis1910—320.[printed]| Elmomorphus brevicornis [handwritten] | Elmomorphus brevicornis. [handwritten] | Elmomorphus brevicornis Sharp det. H. Bollow 1934 [handwritten and printed]”; NHMUK • 1 ♀ (Fig. 4A–B); “ Elmomorphus brevicornis Type D.S. [David Sharp] Jokio [sic]. Japan Lewis. [handwritten] | Japan. G.Lewis [printed] | Sharp Coll. 1905-313. [printed] | Type [printed, round label with red frame]”; NHMUK. Additional material JAPAN • 1 ♀; “ Shimakatsu Mie-Pref. 16.XI.1958 Coll. Shozo Ishida | Elmomorphus brevicornis Sharp Det. M. SATO 1971 ”; NHMW • 1 ♂; “ Nagara-River Gifu-City 26.VII.1951 Coll. Zen. Naruse ”; NHMW • 1 ♂; “ Kurokawa, N-Echigo 2.IX.1960 Col. K. Baba ”; NHMW • 1 ♂; “ Kabuchi-gawa Gifu Pref. 18.VIII.1967 M. Sato leg.”; NHMW • 10 ♂♂, 6 ♀♀; “ Japan, Shimane Pref.: Matsue: Yakumo 26.–30. iii.2019 M. Hayashi ”; JKCB • 5 ♂♂, 3 ♀♀; “ Japan, Shimane Pref.: Izumo, Nishitani 30.iii.2019 M. Hayashi ”; JKCB • 1 ♀; “ NE-JAPAN Miyagi Pr., Mts. Abukuma, 6.6. Uchikawa riv., leg. Ohmomo 1987 | Elmomorphus brevicornis Sharp ”; NHMW. SOUTH KOREA • 1 ♂, 1 spec. sex not examined; “ South Korea, Jeollabuk-do, Buan-gun, Byeonsanmyeon, Junggye-ri, Jiko Falls 15.VI.2011, leg. S.W.Jung ”; NHMW. Note The original description was based on two specimens collected by G. Lewis. Both specimens are still preserved in the collection of David Sharp in the NHMUK. The female specimen is glued on a larger rectangular card with the following handwritten text: “ Elmomorphus brevicornis Type D.S. Jokio. Japan Lewis.”. This style of labelling and label text is typical of David Sharp’s type material. The male specimen and the dissected aedeagus are glued on one card, while its detached appendages are glued on a second card, pinned below the specimen. The two syntypes are conspecific. However, while the type locality mentioned in the original description (“Kobé”) is written on the original label of the male specimen (Fig. 4C), the name “Jokio” [Sharp’s spelling of Tokyo] is found on the label of the female specimen (Fig. 4A). Since no other species is known from Honshu and since taxonomic confusion is improbable, a lectotype designation is considered unnecessary (see ICZN 1999: Recommendation 74G, https://www.iczn.org/the-code/declaration-44-amendment-of-article-74-7-3/). In the abstract of their most remarkable article, Devi et al. (2016: 371) wrote that “A lectotype is designated for this species [Elmomorphus brevicornis]”. However, the term “ lectotype ” is not used anywhere else in their article, and it does not contain sufficient information to ensure recognition of the specimen designated. Therefore, the requirements of the International Code of Zoological Nomenclature (ICZN 1999: Art. 74.7) are not fulfilled. Diagnosis Elmomorphus brevicornis is a medium-sized (TL 2.59–3.51 mm), elongated oval, dorsally moderately convex species, with the highest point at the anterior third of the elytral length (lateral view). Body outline discontinuous between pronotum and elytra; yellowish plastron microscales cover the entire surface of the cranium, lateral portions of the pronotum and the entire dorsal surface of the elytra, so most of the dorsal surface appears to be matt (Fig. 5A). Each elytron has nine rows of large round punctures arranged in shallow striae. Legs conspicuously long and robust, only moderately shorter than the combined length of pronotum and elytra. Elmomorphus brevicornis closely resembles E. amamiensis in external morphology, and it can be distinguished by the following characteristics: (1) elytral sides in E. brevicornis subparallel in the anterior half, while in E. amamiensis they are arcuate and more convergent (Fig. 5B), thus the outline appears to be generally broader and less oval in E. brevicornis; (2) sides of pronotum usually more rounded in E. brevicornis, while they are almost straight in E. amamiensis; (3) males of E. brevicornis with several longer setae in a transverse row on the labrum, and with similar setae in two pairs of clusters on each prosternal process and on the admedian portions of metaventrite, row and clusters of setae rather inconspicuous (Fig. 6A, C, E); similar, longer setae also near the apex of the fifth ventrite (Fig. 7D); in the male of E. amamiensis the setal row and all setal clusters are well developed, conspicuous (Figs 6B, D, F, 7E); (4) parameres weakly curved ventrad in E. brevicornis (Fig. 8B), but strongly curved in E. amamiensis (Fig. 8D); (5) bursa copulatrix of the two species distally with one cluster of microspines on each side (Fig. 9D), while in E. amamiensis, besides these microspines there are several additional larger sclerites (Fig. 9E). Except for differences in the morphological characters, the two species differ by 22.7–23.9% in the partial mtDNA encoding for cytochrome c oxidase subunit I. Measurements (mm) TL: ♂♂ 2.89–3.38 (3.10 ± 0.13, n = 14), ♀♀ 3.15–3.51 (3.34 ± 0.12, n = 7); PL: ♂♂ 0.65–0.85 (0.78 ± 0.05, n = 14), ♀♀ 0.75–0.90 (0.83 ± 0.05, n = 7); PW: ♂♂ 1.20–1.43 (1.33 ± 0.06, n = 14), ♀♀ 1.30–1.47 (1.40 ± 0.06, n = 7); EL: ♂♂ 2.22–2.57 (2.42 ± 0.09, n = 14), ♀♀ 2.50–2.86 (2.66 ± 0.11, n = 7); EW: ♂♂ 1.44–1.66 (1.54 ± 0.05, n = 14), ♀♀ 1.51–1.77 (1.65 ± 0.09, n = 7); MsTL: ♂♂ 0.82– 0.94 (0.88 ± 0.03, n = 14), ♀♀ 0.87–0.97 (0.91 ± 0.03, n = 7); MtTL: ♂♂ 0.91–1.09 (1.02 ± 0.05, n = 14), ♀♀ 0.97–1.12 (1.06 ± 0.05, n = 7); PhL: 0.73–0.89 (0.83 ± 0.04, n = 11); PrL: 0.32–0.39 (0.37 ± 0.02, n = 11). Redescription BODY. Elongated oval, widest behind mid-length of elytra, moderately convex dorsally, with the highest point at anterior third of elytral length (lateral view).Colouration black, except reddish-brown mouthparts, antennal clubs, tarsi, claws, trochanters, and ventral portions of femora. Tibiae and remainder of femoral surface dark brown to black. Dorsal pubescence consists mainly of short, thin decumbent yellowish setae arising from small punctures. Plastron microscales (Fig. 7B) on the entire cranium, on pronotum in two lateral bands, covering ca 0.2 of pronotal width on each side, and on the entire surface of elytra. Ventral surface with dense, thin plastron hair-like setae (Fig. 7C) except for prosternal process and median part of metaventrite. HEAD. Dorsally entirely covered with plastron scales and with round, setiferous punctures; puncture diameter ca 0.75× diameter of an eye facet, and their distance varies between 0.50–1.00× of a facet diameter. Labrum transverse, with anterior margin straight; anterolateral angles rounded; exposed portion microreticulate, with small setiferous punctures; two types of hair-like setae present, short decumbent setae on most of the surface, and several longer semi-erect setae in a hardly discernible transverse row near mid-length (Fig. 6A), setae nearly half as long as ID and more obvious in males (in older material long setae often abraded). Clypeus with anterior margin straight and with a row of the fine short hairs. Eyes oval, protruding and large, interfacetal setae short; ID: ♂♂ 0.38–0.43 mm (0.41 ± 0.02, n = 14), ♀♀ 0.42–0.48 mm (0.44 ± 0.02, n = 7); APD/ID: ♂♂ 1.93–2.09 (2.01 ± 0.04, n = 14), ♀♀ 1.89–2.04 (1.96 ± 0.05, n = 7). Antennae short, reaching slightly behind middle of eyes, 10-segmented; densely covered by plastron; each club segment with a conspicuous peg-like sensillum on anterior face and numerous hair-like, peg-like and branched sensilla; scape and pedicel small and subequal in length, not enlarged. THORAX. Pronotum transverse, widest at base, strongly convex, PW/PL: ♂♂ 1.60–1.85 (1.72 ± 0.07, n = 14), ♀♀ 1.60–1.76 (1.68 ± 0.05, n = 7); plastron in lateral band on each side along entire pronotal length, mesally reaching level of third elytral row; disc smooth, shiny, with large round setiferous punctures, punctures nearly as large as facets, separated by 0.50–1.00× of a facet diameter; punctures on plastron area smaller, similar to those on head. Anterior angles strongly deflexed, protruding and acute, third as long as interocular distance; pronotal sides convergent anteriad, distinctly arcuate near middle, moderately explanate along entire length. Hypomeron widest behind mid-length. Prosternal process wide and short, lateral margins divergent and moderately arcuate; posterior margin widely rounded; lateral portion raised, wide and in male with group of longer setae (Fig. 6C) forming a hardly discernible setal cluster (these setae only moderately longer than other hair-like ventral setae and often abraded); median keel moderately convex, ca ⅓ as wide as width of prosternal process. Scutellum longer than wide, smooth, with small, sparse punctures. Metaventral process with lateral sides strongly raised, anterior margin not raised. Metaventral disc flat in female, finely depressed in male; longitudinal step-like elevation along sides delimits lateral area with plastron from smooth central one, surface irregularly and moderately sparsely punctate and in some specimens finely irregularly wrinkled; discrimen well impressed, distinct; a small, hardly discernible setal cluster present in front of metakatepisternal suture in males on each side of metaventral disc (Fig. 6E). Elytra oblong, widest behind middle; moderately convex dorsally, in dorsal view with the highest point at anterior third; sides subparallel in anterior half, more strongly arcuate in posterior half; EL/EW: ♂♂ 1.53–1.69 (1.57 ± 0.04, n = 14), ♀♀ 1.53–1.66 (1.61 ± 0.04, n = 7); surface entirely covered by plastron scales and with numerous minute punctures distinctly smaller than a facet diameter, punctures separated by about 0.50–1.00× a facet diameter. Strial punctures large and deep on elytral disc and subequal in size with facet size, laterad and posteriad progressively smaller. All tibiae straight, to slightly bent near mid-length; protibia ca 1.25× as long as protarsus; PrTL/PL: ♂♂ 1.01–1.20 (1.10 ± 0.05, n = 14), ♀♀ 1.00–1.08 (1.05 ± 0.03, n = 7). Terminal tarsomere in male foreleg ca 1.20× as long as all preceding tarsomeres combined; male foreclaws strongly curved, not widened or thickened, about half of terminal tarsomere length, both similar to each other (Fig. 7A) and similar to female foreclaws. ABDOMEN. All ventrites completely covered with plastron; ventrites 1–5 with a length ratio about 1.00: 0.76: 0.60: 0.40: 1.26 in male, and 1.00: 0.90: 0.73: 0.60: 1.60 in female; intercoxal process wide, about twice as wide as long, subtriangular, sides moderately arcuate; admedian keels feebly raised, reaching posterior margin of ventrite. Male ventrite 5 near anterior margin declivous and then shortly flattened, laterad and posteriad evenly deflexed; apex with distinct triangular excision (Fig. 7D); several longer semi-erect setae on each side of excision in hardly discernible clusters. Female ventrite 5 evenly convex and not flattened anteriorly, with minute longitudinal smooth keel at apex and few longer setae alongside keel; apex rounded. Sternite VIII moderately sclerotized laterally, membranous medially, in males with short strut on anterior margin (Fig. 8E), in females with strut almost as long as abdomen (Fig. 9A). Male sternite IX narrow, with sclerotized anterior strut (Fig. 8F). Aedeagus: phallobase long, narrow, expanded proximally (Fig. 8A), PhL/PrL: 2.14–2.36 (2.24 ± 0.07, n = 11); parameres slightly curved ventrad along apical half, nearly straight, with apices narrowly rounded (Fig. 8B); apex of penis slightly expanded and rounded in lateral aspect, not reaching apex of parameres; ventral sclerotized fibula absent. Ovipositor heavily sclerotized; right coxite ca 1.40× as long as left one; paraproct ca 1.80× as long as right coxite (Fig. 9B). Bursa copulatrix with a cluster of numerous minute spines arranged on each side of distal portions (Fig. 9D). Spermatheca tubular; accessory gland large, semi-tubular. Sexual dimorphism Females are, on average longer and broader than males. For an unambiguous distinction between males and females, the apex of the fifth ventrite should be examined: it is distinctly excised in males (Fig. 7D), while it is rounded, with a short, smooth keel in females. The presence of several longer semi-erect setae on the labrum, prosternal process, metaventral disc and on the apex of the fifth ventrite in males is hard to observe even in well-preserved specimens, and even under a high-quality microscope at a magnification of about 100×. Distribution Japan: Honshu, Izu-Ôshima, Oki, Shikoku, Kyushu, Tsushima, and Tanegashima (Nakajima et al. 2020); South Korea (Fig. 10A). Devi et al. (2016) erroneously recorded E. brevicornis from India. Their record was published in the unreviewed “ Journal of Entomology and Zoology Studies ”, a so-called predatory journal (see https://predatoryjournals.com/journals/). The “redescription” provided in this article does not allow any conclusions to be drawn on the identity of the specimens. The “Aedagues” [sic] depicted in their fig. 1c is, in fact, an ovipositor! Judging from their habitus photograph (fig. 1a), these specimens, beyond any doubt, do not belong to E. brevicornis or any other species similar to E. brevicornis. Immature stages The larva was described by Hayashi & Kadowaki (2008) and Hayashi (2015). It was found in a river on submerged roots of Salix L. and Carex L. (Hayashi pers. com.).

Elmomorphus amamiensis Nomura, 1959 Figs 5B, 6B, D, F, 7E, 8C–D, 9C, E, 10B Elmomorphus brevicornis amamiensis Nomura, 1959: 33 (original description). Elmomorphus brevicornis amamiensis – Satô 1960: 252; 1965: 90; 1977: 1. — Kodada & Jäch 2006: 442 (catalogue). Elmomorphus amamiensis – Jung & Bae 2014: 5 (new status, distribution). — Kodada & Jäch 2016: 606 (catalogue). — Nakajima et al. 2020: 178, 322 (diagnosis, identification key, photographs of living specimens). Type locality Amami Island, Ryukyu Archipelago, Japan. Type material (not examined) See Jung & Bae (2014: 5). Material examined JAPAN • 1 ♂; “ Amami-Ôshima Shinmura | 13. VI. 1962 M. Sato ”; NHMW • 1 ♂; “(Ryukyus) Yona Okinawa 13.VIII.1969 Y. Hori leg.”; NHMW • 1 ♂; “ Nago-shi, Okinawa-ken 2-5.VIII.1980 Col. K. Baba | Elmomorphus brevicornis amamiensis Nomura Det. M. Sato 1992 ”; NHMW • 4 ♂♂, 4 ♀♀; “ Shinokawa, Setouchi-cho, Amami-Ôshima, Kagoshima, Japan, 28.22513, 129.29986, 5.III.2020, H. Yoshitomi leg.”; JKCB. Diagnosis Elmomorphus amamiensis is medium-sized (TL 2.80–3.22 mm), elongated oval, dorsally moderately convex, with the highest point slightly before the middle of the elytral length (lateral view); body outline slightly discontinuous between pronotum and elytra; plastron microscales covering the entire surface of the cranium, lateral portions of the pronotum and the whole dorsal surface of the elytra (Fig. 5B). Elytron with nine rows of moderately large, round punctures in shallow striae. Legs long and robust, somewhat shorter than the combined length of pronotum and elytra, claws moderately curved. Differences to the morphologically most similar E. brevicornis are discussed above. Measurements (mm) TL: ♂♂ 2.80–2.99 (2.91 ± 0.06, n = 9), ♀♀ 3.09–3.22 (3.16 ± 0.05, n = 7); PL: ♂♂ 0.68–0.77 (0.74 ± 0.03, n = 9), ♀♀ 0.70–0.78 (0.76 ± 0.03, n = 7); PW: ♂♂ 1.14–1.24 (1.20 ± 0.03, n = 9), ♀♀ 1.25–1.35 (1.31 ± 0.03, n = 7); EL: ♂♂ 2.18–2.34 (2.27 ± 0.05, n = 9), ♀♀ 2.42–2.60 (2.50 ± 0.05, n = 7); EW: ♂♂ 1.38–1.46 (1.42 ± 0.02, n = 9), ♀♀ 1.48–1.59 (1.54 ± 0.04, n = 7); MsTL: ♂♂ 0.84– 0.96 (0.92 ± 0.03, n = 9), ♀♀ 0.83–0.87 (0.85 ± 0.01, n = 7); MtTL: ♂♂ 1.03–1.10 (1.07 ± 0.03, n = 9), ♀♀ 0.99–1.04 (1.02 ± 0.02, n = 7); PhL: 0.91–1.19 (1.02 ± 0.08, n = 7); PrL: 0.39–0.43 (0.42 ± 0.01, n = 7). Redescription BODY. Elongated oval, widest behind mid-length of elytra, moderately convex dorsally. Colouration black; mouthparts, antennae, tibiae and tarsi reddish-brown; femora dark brown. Main pubescence consisting of very short and thin, decumbent yellowish setae, which arise from small punctures. Dorsal plastron present on the entire surface except for the pronotal disc. Ventral surface except for prosternal process and disc of metaventrite with hair-like plastron setae. HEAD. With plastron and round setiferous punctures with a diameter of ca 0.75× a facet diameter, punctures separated by distance 0.50–1.00× a facet diameter. Labrum transverse, anterior margin straight, setose; anterolateral angles rounded; exposed portion microreticulate and micropunctate; male with a transverse row of strong, densely set conspicuous setae near middle (Fig. 6B), longest setae laterally, in length subequal to two-third of interocular distance; female with shorter and rather sparse setae, setal row hardly discernible. Anterior margin of clypeus straight, and not in the same plane as labrum. Eyes large, oval, protruding; interfacetal setae sparse, short; ID: ♂♂ 0.37–0.43 mm (0.40 ± 0.02, n = 9), ♀♀ 0.43–0.48 mm (0.44 ± 0.02, n = 7). Antennae 10-segmented, shorter than eye length. THORAX. Pronotum transverse, moderately convex, widest at base, PW/PL: ♂♂ 1.60–1.71 (1.62 ± 0.04, n = 9), ♀♀ 1.66–1.91 (1.73 ± 0.08, n = 7); plastron on entire lateral portions, mesally reaching level of third elytral row; pronotal disc smooth, with large, round setiferous punctures; punctures slightly smaller than facets, nearly regularly spaced, interstices 0.75–1.20× a facet diameter. Anterior angles strongly protruding, acute and deflexed; lateral sides of pronotum convergent anteriad, slightly arcuate or nearly straight, narrowly explanate. Prosternal process with lateral margins divergent, moderately arcuate; posterior margin rounded; lateral portion slightly elevated, separated from median keel by longitudinal depressions; median keel nearly flat, surface finely punctate and irregularly wrinkled. Male with two clusters of conspicuous long setae in anterolateral portions of prosternal process (Fig. 6D), longest setae as long as prosternum in front of prosternal process. Scutellum longer than wide, surface smooth, with small, sparse punctures. Metaventrite along middle ca twice as long as prosternal process; disc flat in males, slightly elevated in females, discrimen present nearly along the entire length, surface finely sparsely punctate, and irregularly wrinkled. Metaventral process as long as prosternal one, with lateral sides keel-like, anterior margin not straight, flat; male with two clusters of conspicuous long setae in posterolateral portions of metaventrite (Fig. 6F). Elytra ovate, widest behind middle; sides moderately arcuate, more convergent posteriad than anteriad, narrowly explanate; EL/EW: ♂♂ 1.57– 1.64 (1.60 ± 0.02, n = 9), ♀♀ 1.57–1.65 (1.62 ± 0.02, n = 7); entire surface with plastron; each elytron with nine striae, strial punctures smaller than facets, separated by distance of 1.00–2.00× puncture diameter; punctures smaller laterad and toward apex. Tibiae all straight, slender; protibia ca 1.25× as long as protarsus; PrTL/PL: ♂♂ 1.12–1.25 (1.19 ± 0.04, n = 9), ♀♀ 1.03–1.21 (1.09 ± 0.05, n = 7). Terminal protarsomere in male ca 1.20× as long as all preceding tarsomeres combined; male foreclaws moderately curved, not widened or thickened, slightly less than half length of the terminal tarsomere length, both similar to each other and similar to female foreclaws. ABDOMEN. Ventrites completely covered with plastron; ventrites 1–5 with length ratio 1.00: 0.74: 0.52: 0.48: 1.66 in male, and 1.00: 0.88: 0.65: 0.57: 1.84 in female. Intercoxal process wide, about twice as wide as long, subtriangular, sides distinctly arcuate; admedian keels indistinct, feebly raised in male, reaching posterior margin of ventrite, but nearly absent in female. Mesal portion of male ventrite 5 flattened on anterior third and strongly deflected posteriad (lateral view); apex with distinct triangular excision and cluster of several long semi-erect setae on each side of excision (Fig. 7E). Female ventrite 5 evenly convex and only indistinctly flattened anteriorly, with minute longitudinal smooth keel at apex and few longer setae alongside keel; apex rounded. Aedeagus: phallobase long, narrow, expanded proximally (Fig. 8C), PhL/PrL: 2.32–2.74 (2.43 ± 0.12, n = 7); parameres strongly curved ventrad, especially in apical half (Fig. 8D), moderately narrowed, apices subacute; penis with apex slightly expanded and rounded in lateral aspect; sclerotized fibula absent. Ovipositor heavily sclerotized; right coxite ca 1.30× as long as left one; paraproct ca 1.52× as long as right coxite (Fig. 9D). Bursa copulatrix with cluster of minute spines on each side of distal portions and with several larger sclerites scattered over proximal portion (Fig. 9E). Sexual dimorphism Females are on average larger than males, and the apex of their fifth ventrite is rounded, while in males it is triangularly excised. Moreover, males have long conspicuous setae arranged in a transverse row on the labrum and in clusters situated on lateral sides of the prosternal process, lateral sides of the metaventrite and on the apex of the fifth ventrite; females lack these groups of long setae. Distribution Elmomorphus amamiensis has been so far recorded only from the Ryukyu Archipelago in Japan (Fig. 10B): Amami Island, Tokunoshima, Okinawa-jima, Iheya-jima, Zamami-shoto, Aka-jima, and Kume-jima (Nakajima et al. 2020).

Key to the adults of the species of Elmomorphus from Japan and Korea 1. Male labrum with several long, rather widely spaced setae arranged in a more or less distinct transverse row (Fig. 6A); similar, moderately longer setae arranged in small clusters on prosternal process and metaventrite (Fig. 6C, E), and on apex of ventrite 5 (Fig. 7D); long setae on labrum maximally half as long as interocular distance, most elongate ventral setae moderately shorter than those on labrum. Parameres in apical half slightly curved ventrad, nearly straight (Fig. 8B). Female: bursa copulatrix with a cluster of minute spines on each side in distal portions (Fig. 9D).................................................................................................................................. E. brevicornis Sharp, 1888 – Male labrum with numerous conspicuously long, closely arranged setae in a transverse row (Fig. 6B); similar setae in extensive clusters on prosternal process, metaventrite (Fig. 6D, F), and on apex of ventrite 5 (Fig. 7E); most elongate setae on labrum about ⅔ of interocular distance, longest ventral setae moderately longer than interocular distance. Parameres in apical half strongly curved (Fig. 8D). Female: bursa copulatrix with cluster of minute spines and with several larger sclerites scattered over its proximal portion (Fig. 9E)...................................... E. amamiensis Nomura, 1959

Mordellochroa humerosa (Rosenhauer, 1847) is reported from Slovakia for the first time based on 13 specimens collected in 2017–2020 in two localities. The known distribution of the species and collection circumstances are discussed, and four mtDNA sequences of COI gene fragment are submitted to GenBank and BOLD. Photographs of the habitus and drawings of the diagnostic characters are provided for M. humerosa.