Revision of the Nearctic species of Acanthocnema Becker, 1894 (Diptera: Scathophagidae)

304 European Journal of Taxonomy 1026: 304–337 https://doi.org/10.5852/ejt.2025.1026.3125 europeanjournaloftaxonomy.eu ISSN 2118-9773 2025 · Sinclair B.J. This work is licensed under a Creative Commons Attribution License (CC BY 4.0) Received: 9 June 2025 • Accepted: 7 October 2025 • Published: 1 December 2025 Topic editor: Tony Robillard • Section editor: Torbjørn Ekrem • Desk editor: Eva-Maria Levermann Research article urn:lsid:zoobank.org:pub:59388C59-E955-4897-AB86-BE6DF1BB303F Revision of the Nearctic species of Acanthocnema Becker, 1894 (Diptera: Scathophagidae) Bradley J. SINCLAIR  Canadian National Collection of Insects & Canadian Food Inspection Agency, OPL-Entomology, K.W. Neatby Bldg., C.E.F., 960 Carling Ave., Ottawa, ON, Canada K1A 0C6. Email: bradley[email protected] Abstract. The Nearctic species of Acanthocnema Becker, 1894 are revised, including the description of three new species: A. albibarba (Loew, 1869), A. capillata (Loew, 1872), A. nigrimana (Zetterstedt, 1846), A. pulchripennis sp. nov., A. rainierensis sp. nov., A. ruficauda Curran, 1929 and A. torrenticola sp. nov. Acanthocnema nigrimanaisnewlyconfirmedfromNorthAmerica.Allspeciesareillustrated, distributionsmappedandanidentificationkeytospeciesispresented.Thelarvalcephaloskeletonand puparium of A. torrenticolasp.nov.arebrieflydescribedandillustratedandthepupariumofA. albibarba is illustrated. Keywords.Aquatic,newspecies,identificationkey,immaturestages. Sinclair B.J. 2025. Revision of the Nearctic species of Acanthocnema Becker, 1894 (Diptera: Scathophagidae). European Journal of Taxonomy 1026: 304–337. https://doi.org/10.5852/ejt.2025.1026.3125 Introduction The family Scathophagidae Robineau-Desvoidy, 1830 isconfinedprimarilytothenorthernhemisphere and includes more than 360 species (Bernasconi & Šifner 2021). Adults appear to be mostly predacious on insects, whereas larvae have varied habits (Vockeroth 1987). Most larvae are phytophagous, including leaf miners, while some larvae are coprophagous in dung and decaying plants or predaceous in plant tissue, water or soil (Vockeroth 1987). Acanthocnema Becker, 1894 is an aquatic genus of Scathophagidae, with adults frequently swept or aspirated from emergent rocks in streams, creeks and small rivers (Figs 1–3) (Suwa 1986; Ozerov & Krivosheina 2018). Females of A. glaucescens (Loew, 1864) have been observed crawling beneath the watertotheundersideofrocksandovipositinginotherflyandcaddisflyeggmasses(Hinton1981), where larvae prey on the eggs (Nelson 1992; Purcell et al. 2008). Acanthocnema has a bivoltine life cycle,withthefirstgenerationofadultsemerginginearlyspringandasecondgenerationinautumn (Nelson 1992; Purcell et al. 2008). Prior to this study, there were 10 described species of Acanthocnema, with three species known from the Nearctic Region, one species described from Nepal and six species from the Palaearctic Region SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 305 (Suwa 1986; Vockeroth 1987; Ozerov & Krivosheina 2018; Ozerov 2019). The genus can be recognized using the key to genera in Vockeroth (1987). In this study, the Nearctic species are revised, including the description of three new species. Material and methods Institutional abbreviations CNC = Canadian National Collection of Insects, Ottawa, Canada DEBU = University of Guelph Insect Collection, Guelph, Canada EMEC = Essig Museum of Entomology, University of California, Berkeley, USA KUMF = Biosystematics Laboratory, Kyushu University, Fukuoka, Japan MCZ = MuseumofComparativeZoology,HarvardUniversity,Cambridge,USA UBCZ = Spencer Entomological Museum, University of British Columbia, Vancouver, Canada USNM= NationalMuseumofNaturalHistory,Washington,USA Numerous specimens from the CNC were partially sorted to species by the late Richard Vockeroth, including manuscript names, which were used in this publication. Label data for primary types are cited from the top downward, with the data in quotation marks. Labels are cited in full with original spelling, punctuation, and date, with label lines delimited by a slash (/) and individual labels delimited by a double slash (//). Additional information is included in square [ ] brackets. Secondary type data are abridged and listed alphabetically. Terms used for adult structures follow those of Cumming & Wood (2017) and those of immature structures follow those of Borkent & Sinclair (2017). Specimens were photographed using Leica Application Suite X (LASX) with a Leica M205C microscope and a Leica DMC5400 camera. Abbreviations used in the material examined sections Cpgd = campground Ck = creek Co. = county Hwy = highway MT = Malaise trap NF = National Forest NP = National Park Pk = park PP = Provincial Park R = river Rd = road Geographic coordinates for collecting localities were compiled for each species using data on the specimen labels. For specimen labels lacking geographic coordinates, latitude and longitude values were estimated by the author using Google Earth or Google Maps and appear in square brackets following the locality name. Coordinates were uploaded to SimpleMappr.net (Shorthouse 2010), which was used to produce the species distribution maps. European Journal of Taxonomy 1026: 304–337 (2025) 306 Results Taxonomy Class Insecta Linnaeus, 1758 Order Diptera Linnaeus, 1758 Family Scathophagidae Robineau-Desvoidy, 1830 Subfamily Scathophaginae Robineau-Desvoidy, 1830 Genus Acanthocnema Becker, 1894 Acanthocnema Becker, 1894: 136 (preocc. Costa, 1859). Name conserved by ICZN (1954: 91). ClinoceroidesHendel,1917: 36.Type species:Cordylura glaucescens Loew, 1864, by original designation. Type species Cordylura nigrimana Zetterstedt, 1846, by original designation. Diagnosis The genus Acanthocnema ischaracterizedbythefollowingcombinationofcharacters(modifiedfrom Ozerov & Krivosheina 2018): arista short pubescent basally, bare apically; palpus elongate, spatulate, Figs 1–3. 1. Bronte Creek, Lowville Park, Burlington, Ontario, Canada. 2. Acanthocnema torrenticola sp. nov., adult, on emergent rock, Grand River, Fergus, Ontario, Canada (photograph by S.A. Marshall). 3. A. torrenticola sp. nov., mating pair, Carroll Creek, Elora, Ontario, Canada (photograph by S.A. Marshall). SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 307 without strong apical / subapical seta; proepisternum with setulae anterior to spiracle; anepisternum covered with setulae along dorsal margin and posteriorly only, without setulae posterior to anterior spiracle; katepisternum with one strong seta in posterodorsal corner; anepimeron bare; postmetacoxal bridge absent; fore femur with or without black spine-like setae ventrally; fore tibia with ventral apical spur, with or without rows of short spinules ventrally; scutellum with a pair of strong apical and a pair of strong basal setae; male sternite 5 usually bilobate posteriorly; ovipositor short and compact, proctiger shifted dorsally bearing long setae; female tergite and sternite 7 fused anteroventrally, tergite 7 subtriangular, strongly tapered and narrowly divided dorsally; female tergite 8 U-shaped, narrowly divided dorsally and encircling proctiger; female sternite 8 divided medially into pair of narrow, tapered lobes. Eggs The egg of A. glaucescenswasillustratedbyHinton(1981:pl.129)withtherespiratoryridgesorhorns surrounding the plastron projecting above the jelly-mass of the host eggs. Larvae The larval instars of A. glaucescensweredescribedandillustratedbyNelson(1992).Thefinalinstaris densely covered in setae, with posterior spiracles surrounded by well-developed lateral tubercles. The mouthhooks have dense and pronounced dentation. The prothoracic spiracles are bicornate with 17 papillae. Puparium ThepupariumwasbrieflydescribedbyNelson(1992)andphotographedbyPurcellet al. (2008). Acanthocnema albibarba (Loew, 1869) Figs 4–12, 63 Cordilura albibarbaLoew,1869:183.Typelocality:NewHampshire,USA. Acanthocnema albibarba – Curran 1929: 133 (new combination). — Vockeroth 1965: 835 (catalogue); 1987:1091,fig.103.33(foreleg). Diagnosis This species is distinguished by the yellowish to yellowish-brown body and legs, base of postpedicel yellow, proepimeral seta present, wing crossveins cloudy, and posthumeral (presutural intra-alar) seta present. Type material Holotype (based on online images: https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:13156) USA – New Hampshire • ♂;“N.H.;albibarba / m. // Loew / Coll. // Type / 13156 [red label] // albibarba / Loew // MCZ-ENT / 00013156 / data matrix code”; MCZ. Other material examined CANADA – Newfoundland and Labrador • 1♀;St.John’s,Agric.Exp.Stn.;[47.514°N,52.784°W]; 20 Jul. 1967; J.F. McAlpine leg.; CNC. – Nova Scotia • 1♀;CapeBretonHighlandsNP,LoneShieling; [46.810°N,60.733°W];11Jul.1983;J.R.Vockerothleg.;sweptalongfastrockystream;CNC.– Ontario • 1♀;Dunrobin;[45.42°N,76.02°W];28May1967;H.J.Teskeyleg.;CNC• 1♀,1puparium; European Journal of Taxonomy 1026: 304–337 (2025) 308 Fergus;[43.691°N,80.386°W];18Apr.1993;S.A.Marshallleg.;pupariuminwatercress;DEBU.– Quebec • 1♀;Abbotsford;[45.443°N,72.863°W];29May1968;G.E.Shewellleg.;CNC. USA – Maine • 1♂,1♀;MtKatahdin,HuntTrail;[45°53′44″N,68°58′53″W];1600–2400fta.s.l.; 1–6 Jul. 1968; D.M. Wood leg.; CNC • 1♂;samedataasforpreceding;KUMF• 1♀;samedata asforpreceding;[45°53′53″N,68°57′14″W];3800fta.s.l.;29Jun.1968;CNC• 1♀;Pittston; [44°13′18″N,69°45′20″W];3Aug.1930;A.L.Melanderleg.;USNM.–New Hampshire • 1♂;Lost River;[44.020°N,71.742°W];7Jul.1931;A.L.Melanderleg.;USNM• 1♀;WhiteMtns,TheFlume; [44°06′N,71°14′W];7Jul.1938;A.L.Melanderleg.;USNM• 1♀;WhiteMtns,Morrison;USNM.– New York • 1♀;Adirondacks,AvalancheTrail;[44.182°N,73.963°W];30Jul.1929;A.L.Melander leg.; CNC • 1♂;WhitefaceMt;[44°22′43″N,73°53′06″W];4000fta.s.l.;19Jul.1962;J.R.Vockeroth leg.; CNC. – Vermont • 1♀;Peru;[43.233°N,72.893°W];15Jul.1931;A.L.Melanderleg.;USNM. Description Body yellowish to yellowish brown, with dense white pruinescence. Body length: 4.2–5 mm; wing length: 4.3–5.0 mm. Figs 4–7. Acanthocnema albibarba (Loew, 1869), ♂ (CNC), Mt Katahdin. 4.Head,obliquelateralview. 5.Habitus,lateralview.6. Thorax, lateral view. 7. Wing. Abbreviations: presut ial s = presutural intra-alar seta; prepm s = proepimeral seta; R2+3 = second branch of radial view. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 309 Male Head (Fig. 4). Frontal vitta yellow to yellowish brown anteriorly, matt; fronto-orbital plate brown, with numerous dark setulae. Chaetotaxy: anterior orbital seta proclinate, posterior 2 orbital setae lateroclinate; 3 inclinate frontals; 1 ocellar, 1 inner vertical, 1 outer vertical; postocellar setae weak, divergent; row of dark postocular setae; 1 vibrissa, 1 strong subvibrissa. Gena silvery pruinescent, depth one-quarter eye height; postgenal setae white, soft, longer than width of postgena. Face, parafacial and occiput silvery pruinescent. Palpus yellowish white with long white setae. Proboscis with broad, shiny prementum, with long scattered white setae, longer than width of prementum. Antenna brown, postpedicel yellow at base Figs 8–10. Acanthocnema albibarba (Loew, 1869), ♂ (CNC), Whiteface Mt. 8. Abdomen, ventral view. 9. Terminalia posterior view. 10. Terminalia, lateral view. European Journal of Taxonomy 1026: 304–337 (2025) 310 of arista insertion; postpedicel rounded apically, 2 × as long as broad. Arista pubescent on basal third and bare apically. THorax (Figs 5–6). Dark brown, paler laterally; whitish vitta along acrostichal series anteriorly. Acrostichals biserial, short, slender; 2+3 dorsocentrals; 1+2 intra-alars; 1+1 supra-alars; 1–2 postpronotals; 2 notopleurals, 2 postalars; scutellum with pair of strong apical setae and pair of strong basal setae; scutellar disc with a few scattered setulae. Proepisternal seta present. Proepimeral seta present. Anepisternum with dark setulae on posterior half and 1 long seta and several long thinner setae near posterior margin. Katepisternum with 1 strong, long seta in posterodorsal corner and numerous yellow setulae. Legs (Fig. 5). Yellow, slightly darker apically or posterior face of femora and tibia brown. Fore femur with 3 posteroventral setae extending beyond dense setulae; 5–6 evenly spaced dorsal setae, shorter than width of femur. Fore tibia with ventral apical spur, 1 anterodorsal slightly beyond mid-length, 1 preapical dorsal seta and 1 posteroventral seta proximal to spur; biserial row of short spinules ventrally. Fore tarsomere 1 with dense mat of anterior setulae. Mid femur with 2 long anteroventral setae on basal half; row of 5–6 anterior setae; 1 preapical anterior and 2 posterior preapical setae. Mid tibia with 1 anterodorsal seta beyond mid-length and 1 preapical dorsal seta; 1 anteroventral seta and 1 posteroventral apicalseta.Hindfemurwithrowof4–6anterodorsalsetae;severalwidelyspacedanteroventraland posteroventralsetae.Hindtibiausuallywith2anterodorsalsetaeoneithersideofmid-length;1 posterodorsal seta near mid-length; 1 dorsal preapical seta; 1 anteroventral apical seta. Wing (Fig. 7). Infuscate, with clouding about apex of R1 and r-m and dm-m crossveins and R2+3 distal to cell dm; veins black; crossvein dm-m nearly at right angles, not aligned with M4; M4 beyond cell dm weakened to wing margin, one-half length of crossvein dm-m; CuA+CuP weakened beyond basal third, not reaching wing margin. Calypteres and halter yellow. abdomen. Similar to thorax, brownish dorsally, with greyish pruinescence; with long setae. Sternite 4 slightly wider than long (Fig. 8). Sternite 5 broad, with pair of cylindrical lobes; long setae on basal half of lobes, apex slightly boot-shaped (Fig. 8). Terminalia (Figs 9–10): Epandrium rounded, narrow with long setae, especially ventrolateral setae long and wavy, nearly as long as height of epandrium. Cercus Figs 11–12. Acanthocnema albibarba (Loew, 1869), puparium (DEBU), Fergus. 11. Terminal segment, caudal view. 12. Terminal segments, dorsal view. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 311 short, apical margin rounded in lateral view; cerci closely approximated medially, with setae longer than cercus.Surstylusdigitiform,somewhatflattened;apexrounded,withmedialmarginaltip;longwavy setae on apical half, longer than length of surstylus (projecting free in dry, undissected specimens). Phallapodeme elongate, rod-shaped. Pregonite strongly recurved with several long setae at mid-length; apexflattenedwithsingleshortsubapicalseta.Postgonitegentlyarchedwithroundedapex.Ejaculatory apodeme C-shaped with expanded ejaculatory duct. Distiphallus sickle-shaped with jagged inner margin. Female Similar to male except, palpus yellowish brown; without long pale setae on occiput and proboscis; abdomen dark, subshiny; terminalia not dissected. Distribution This species is known from northeastern North America, recorded from Newfoundland to central southern Ontario (Fig. 63). Remarks A female specimen was reared from a puparium (Figs 11–12) collected in watercress. The fore leg of this specieswasillustratedinVockeroth(1987:fig.33). Acanthocnema capillata (Loew, 1872) Figs 13–20, 61 Cordilura capillata Loew, 1872: 98. Typelocality:NewHampshire,USA. Acanthocnema capillata – Curran 1929: 133 (new combination). — Vockeroth 1965: 835 (catalogue). Diagnosis This species is distinguished by the blackish ground colour, male palpus yellow, orbital setae lateroclinate, fore tibia with row of short, strong, black anteroventral setae proximal to ventral preapical spur and male sternite 5 with paired apical lobes. Type material Holotype (based on online images: https://mczbase.mcz.harvard.edu/guid/MCZ:Ent:13158) USA – New Hampshire • ♀;“N.H.//capillata / m. // Loew / Col l. // Type / 13158 [red label] // MCZENT / 00013158 / data matrix code”; MCZ. Other material examined CANADA – Quebec • 1♂;ForillonNP,Gaspésie,LaChuteTrail;48°50′N,64°16′W;24Aug.2016; B.J. Sinclair leg.; waterfall spray zone; CNC • 2♂;MtOrford;[45.328°N,72.186°W];29Aug.1937; G.E. Shewell leg.; compared with holotype by Vockeroth, 1960; CNC. USA – Maine • 1♂,1♀;MtKatahdin,HuntTrail;[45°53′44″N,68°58′53″W];1600–2400fta.s.l.; 1–6 Jul. 1968; D.M. Wood leg.; CNC. Description Body blackish in ground colour, densely blue-grey pruinescent laterally, dark brown dorsally. Body length: 4–5 mm; wing length: 4.2–4.6 mm. European Journal of Taxonomy 1026: 304–337 (2025) 312 Male Head (Figs 13–15). Frontal vitta black, paler ventrally, matt; fronto-orbital plate black, grey pruinescent, with numerous black setulae. Chaetotaxy: 3 lateroclinate orbitals; 2 inclinate frontals; 1 ocellar, 1 inner vertical, 1 outer vertical; postocellar setae absent; row of dark postocular setae; 1 vibrissa, 1 strong subvibrissa. Gena silvery pruinescent, broad, depth below eye subequal to length of postpedicel; postgenal setae white to golden, soft, slightly shorter than width of postgena. Face, parafacial and occiput silvery pruinescent. Palpus yellow with long white setae. Proboscis with broad, shiny prementum, without setae. Antenna black; postpedicel rounded apically, 2 × as long as broad. Arista pubescent, bare on apical third. THorax (Fig. 16). Dark brown with greyish postpropronotal lobe, lower notopleuron and scutellum; indistinct whitish vitta along acrostichal series anteriorly; pleura and mediotergite with greyish pruinescence. Acrostichals biserial, short, slender; 2+4 dorsocentrals; 1+2 intra-alars; 1+1 supra-alars; 1 postpronotal; 2 notopleurals, 1 postalar; scutellum with pair of strong apical setae and pair of strong basal setae; lateral margins and dorsal surface of scutellum apically with black setae and setulae. Pale proepisternal seta present. Proepimeral seta dark. Anepisternum with dark setae on posterior half and Figs 13–17. Acanthocnema capillata (Loew, 1872). 13–16.♂(CNC),MtKatahdin.13.Head,lateral view. 14.Head,dorsalview.15.Head,dorsolateralview.16.Habitus,lateralview.17.♂(CNC),Mt Orford, fore legs, lateral view. Abbreviation: lc orb s = lateroclinate orbital setae. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 319 posteroventral setae on basal half, shorter than width of femur; row of 5–6 anterior setae; 1 preapical anterior seta and 1 posterior preapical seta. Mid tibia with 1 anterodorsal seta beyond mid-length and 1 preapicaldorsalseta;1anteroventralsetaand1posteroventralapicalseta.Hindfemurwithrowof4–6 anterodorsalsetae;severalwidelyspacedposteroventralsetae.Hindtibiawith3anterodorsalsetae;1 posterodorsal seta near mid-length; 1 dorsal preapical seta; 1 anteroventral apical seta. Figs 32–34. Acanthocnema pulchripennis sp.nov.,paratype,♂(CNC),LisadeleLake.32. Abdomen, ventral view. 33. Terminalia, posterior view. 34. Terminalia, lateral view. European Journal of Taxonomy 1026: 304–337 (2025) 320 W ing (Fig. 31). Infuscate, with discal crossband from costa to M4, without dark spot at apex of M1, veins black; crossvein dm-m obliquely aligned with M4; M4 beyond cell dm strong to wing margin, one-third length of crossvein dm-m; CuA+CuP weakened but reaching wing margin. Calypteres and halter yellow. abdomen. Darker dorsally than thorax, with greyish pruinescence; with long erect setae on tergite 2 anteriorly. Sternites 3 and 4 expanded laterally with elongate setae (Fig. 32). Sternite 5 broad, with pair of cylindrical lobes with long setae, apex slightly tapered and incurved (Fig. 32). Terminalia (Figs 33–34): Epandrium rounded, narrow with short setae. Cercus short, apical margin rounded in lateral view; cerci closely approximated medially, with setae longer than cercus. Surstylus digitiform, apex tapered, with wavy setae of various lengths, some longer than length of surstylus. Phallapodeme elongate, rod-shaped. Pregonite strongly recurved on distal half, with 1 short seta at mid-length; apex tapered to point with severalshortsubapicalsetae.Postgonitegentlyarchedwithroundedapex.Ejaculatoryapodemeflattened and expanded with tapered ejaculatory duct. Distiphallus narrow, tube-shaped with jagged inner margin. Female Similar to male except, abdomen darker, lacking long lateral setae on sternites 3 and 4; terminalia not dissected. Distribution This species is known from northwestern North America, recorded from Yukon to southern British Columbia (Fig. 62). Acanthocnema rainierensis sp. nov. urn:lsid:zoobank.org:act:6B8D324D-49B8-43C3-AEB4-A2AC7988C10A Figs 35–40, 62 Diagnosis This species is distinguished by the yellowish body, proepimeral seta present, fore femur with four long, spine-like posteroventral setae and distal row of strong posteroventral setae, wing with discal crossband and dark spot at apex of M1, and crossvein dm-m not aligned with apex of M4. Etymology The species is named after the type locality, Mt Rainier National Park. Type material Holotype USA – Washington •♂;“MtRainier,Wn[Washington]/VanTrumpCrk[46°47′34″N,121°46′33″W] /Sep.1,1917/A.L.Melander//ALMelander/Collection/1961//HOLOTYPE/Acanthocnema / rainierensis / Sinclair [red label]”; USNM. Paratypes USA – Washington •1♀;samedataasforholotype;USNM•1♀;MtRainier,Longmire;[46°44′56″N, 121°48′51″W];18Jul.1922;A.L.Melanderleg.;USNM•1♂;MtRainierNP,WonderlandTrail, NaradaFallstoCougarRock;46°46′22.11″N,121°44′52.30″W;1317ma.s.l.;29Jul.2016;R.J.Pivar leg.; creek; CNC, CNC5288369. Description Body yellowish laterally and brown dorsally (Fig. 35), with dense white pruinescence. Body length: 4.4–5.0 mm; wing length: 4.4–4.7 mm. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 321 Male H ead (Fig. 35). Frontal vitta yellow to yellowish brown anteriorly, matt; fronto-orbital plate brown, with numerous dark setulae. Chaetotaxy: anterior orbital seta proclinate, posterior 2 orbital setae lateroclinate; 3 inclinate frontals; 1 ocellar, 1 inner vertical, 1 outer vertical; postocellar setae weak, divergent; row of dark postocular setae; 1 vibrissa, 1 strong subvibrissa. Gena silvery pruinescent, depth one-quarter eye height; postgenal setae white, soft, length shorter than width of postgena. Face, parafacial and occiput silvery pruinescent. Palpus yellowish white with white setae. Proboscis with broad, shiny prementum, with scattered white setae, shorter than width of prementum. Antenna dark, with inner face of pedicel and inner basal half of postpedicel yellow; postpedicel rounded apically, 2 × as long as broad. Arista pubescent on basal third and bare apically. Figs 35–37. Acanthocnema rainierensis sp. nov. 35.Holotype,♂(USNM),habitus,lateralview. 36.Paratype,♀(USNM),VanTrumpCk,foreleg,lateralview.37.Holotype,♂(USNM),wing. Abbreviation: dm-m = discal medial crossvein. European Journal of Taxonomy 1026: 304–337 (2025) 322 THorax (Fig. 35). Brown dorsally, broadly yellow laterally; greyish vitta along acrostichal series. Acrostichals biserial, short, slender; 1–2+3 dorsocentrals; 1+2 intra-alars; 1+1 supra-alars; 1 postpronotal; 2 notopleurals, 2 postalars; scutellum with pair of strong apical setae and pair of strong basal setae; scutellar disc with few scattered setulae. Proepisternal seta present. Proepimeral seta present. Anepisternum with dark setulae on posterior half and 1 long seta and several long thinner setae near posterior margin. Katepisternum with 1 strong, long seta in posterodorsal corner and numerous yellow setulae. Figs 38–40. Acanthocnema rainierensis sp.nov.,paratype,♂(CNC5288369).38. Abdomen, ventral view. 39. Terminalia, posterior view. 40. Terminalia, lateral view. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 323 Legs (Fig. 36). Yellow. Fore femur with 4 posteroventral spine-like setae on basal half, longer than width of basalmost seta; row of strong posteroventral setae on distal half; distinct row of anteroventral setae, stronger near mid-length; 4 posterodorsal setae on apical half, shorter than width of femur. Fore tibia with ventral apical spur; 1 anterodorsal slightly proximal to mid-length, 1 posteroventral near mid-length and 1 preapical dorsal seta; biserial row of short spinules ventrally. Fore tarsomere 1 with dense mat of anterior setulae. Mid femur with 4 long posteroventral setae on basal half, several longer than width of femur; row of anteroventral setae on distal half, shorter than width of femur; row of 5–6 anterior setae; 1 preapical anterior seta and 1 posterior preapical seta. Mid tibia with 1 anterodorsal seta beyond midlengthand1preapicalanterodorsalseta;1anteroventralsetaand1posteroventralapicalseta.Hindfemur withrowof4–6anterodorsalsetae;1–2distalanteroventralsetae.Hindtibiawith3anterodorsalsetae; 1 posterodorsal seta near mid-length; 1 dorsal preapical seta; 1 anteroventral apical seta. Wing (Fig. 37). Infuscate, with discal crossband from costa to M 4 and dark spot at apex of M 1 , veins black; crossvein dm-m not aligned with M 4 ; M 4 beyond cell dm weakened apically, reaching wing margin, more than one-half length of crossvein dm-m; CuA+CuP weakened but reaching wing margin. Calypteres and halter yellow. abdomen. Dark dorsally, similar to thorax, with greyish pruinescence; with long erect setae on tergite 2 anteriorly. Sternites 3 and 4 expanded laterally with elongate setae (Fig. 38). Sternite 5 broadly expanded laterally with elongate setae, with pair of triangular lobes with narrow, incurved apex (Fig. 38). Terminalia (Figs 39–40): Epandrium rounded, narrow with short setae; prolonged ventrally beyond base of surstylus. Cercus short, apical margin rounded in lateral view; cerci closely approximated medially, with short apical setae. Surstylus digitiform; distal half expanded laterally, with wavy setae of various lengths, some longer than length of surstylus. Phallapodeme elongate, rod-shaped. Pregonite strongly recurved on distal half; apex tapered to rounded point with single short subapical seta. Postgonite gently archedwithroundedapex.Ejaculatoryapodemeflattenedwithexpandedejaculatoryduct.Distiphallus narrow, tube-shaped with jagged inner margin. Female Similar to male except, abdomen darker, lacking long lateral setae on sternites 3 and 4; tergite 7 subtriangular, fused with sternite 7, dorsally tapered and medially divided; tergite 8 U-shaped, enclosing proctiger, narrowly divided medially, obliquely angled; sternite 8 divided into pair of tapered digitiform lobes, directed dorsally with pointed apex; epiproct and hypoproct small, triangular; cercus oval, thinly sclerotized. Three spermathecae tubular, narrow and recurved posteriorly into duct, expanded anteriorly. Distribution This species is currently known only from Mt Rainier National Park in the state of Washington, USA (Fig. 62). Acanthocnema ruficauda Curran, 1929 Figs 41–48, 62 Acanthocnema ruficauda Curran, 1929: 133. Type locality: Tennessee Pass, Colorado, USA. Diagnosis This species is distinguished by the brownish body and yellowish legs, male postpedicel yellow, anterior orbital seta proclinate, proepimeral seta absent, wing infuscate, and male postgena, prementum and fore coxae with long silky white setae. European Journal of Taxonomy 1026: 304–337 (2025) 324 Type material Holotype USA – Colorado •♂;“TennesseePass[39°21′45″N,106°18′40″W]/10240ftColo//JMAldrich/ VII-[2?]7 coll // Type No. / 41178 / U.S.N.M. [red label] // Acanthocnema / TYPE / ruficauda / Curran [red label] // Acanthocnema / ruficauda/Curran/det./C.H.Curran//USNMENT/01234705[data matrix]”; USNM. Figs 41–44. Acanthocnema ruficauda Curran, 1929. 41–43.Holotype,♂(USNM).41.Habitus,lateral view. 42.Head,lateralview.43.Head,dorsolateralview.44.Paratype,♂(CNC828172),abdomen, lateral view. Abbreviations: lc orb s = lateroclinate orbital setae; pc orb s = proclinate orbital seta. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 325 Figs 45–48. Acanthocnema ruficauda Curran, 1929. 45–46.Holotype,♂(USNM).45. Abdomen and terminalia, ventral view. 46. Male terminalia, lateral view. 47–48.Paratype,♀(CNC),MtEvans. 47. Abdomen, lateral view. 48. Terminalia, ventral view. European Journal of Taxonomy 1026: 304–337 (2025) 326 Other material examined USA – Colorado •1♀;MtEvans,DoolittleRanch;[39°40′34″N,105°36′08″W];9800fta.s.l.;25Jul. 1961; W.R.M. Mason leg.; CNC •1♂;SanJuanCo.,PastureCk;37°38′48″N,107°50′55″W;10154ft a.s.l.; 18 Jun. 2017; J.M. Cumming leg.; CNC. – New Mexico •1♂;OteroCo.,SacramentoMtns,Bluff Springs,ca16mi.ofWMayhill;[32.831°N,105.738°W];8000fta.s.l.;15Aug.1993;J.E.O’Hara leg.; CNC, CNC828172. Description Body brownish (Fig. 41), with dense white pruinescence. Body length: 5.5–6 mm; wing length: 5.8– 5.9 mm. Male Head (Figs 41–43). Frontal vitta yellow to orange anteriorly, matt; fronto-orbital plate brown, with numerous dark setulae. Chaetotaxy: anterior orbital seta proclinate, posterior 2 orbital setae lateroclinate; 3–4 inclinate frontals; 1 ocellar, 1 inner vertical, 1 outer vertical; postocellar setae weak, divergent; row of dark postocular setae; 1 vibrissa, 1–2 strong subvibrissae. Gena yellow with silvery-white pruinescence, depth one-third eye height; postgenal setae white, soft, silky and wavy, longer than width of postgena. Face, parafacial and occiput silvery pruinescent. Palpus yellowish white with long white setae. Proboscis with broad, shiny prementum, with long silky, wavy setae, similar to postgenal setae. Antenna with scape and pedicel yellow to brownish, postpedicel yellow; postpedicel rounded apically, 2 × as long as broad. Arista pubescent on basal third and bare apically. THorax (Fig. 41). Brown, darker beneath dorsocentral row. Acrostichals biserial, short, slender; 2+3 dorsocentrals; 0+2 intra-alars; 1–2+1 supra-alars; 1 postpronotal; 2 notopleurals, 2 postalars; scutellum with pair of strong apical setae and pair of strong basal setae; scutellar disc with a few scattered setulae. Proepisternal seta present. Proepimeral seta absent (Fig. 42). Anepisternum with dark setulae on posterior half and 1 long seta and several long thinner setae near posterior margin. Katepisternum with 1 strong, long seta in posterodorsal corner and numerous yellow setulae. Legs (Fig. 41). Yellowish brown. Fore femur with row of 5–6 widely spaced, pale posteroventral setae extending beyond long, dense setulae; 5–6 evenly spaced dark dorsal setae, shorter than width of femur. Fore tibia with ventral apical spur, 1 anterodorsal slightly beyond mid-length, 1 preapical dorsal seta and 1 posteroventral seta proximal to spur; biserial row of short anteroventral spinules; long posteroventral setae near mid-length, longer than width of tibia. Fore tarsomere 1 with dense mat of anterior setulae. Mid femur with row of 5–6 widely spaced, extending beyond long, dense setulae; row of 5–6 anterior setae; 1 preapical anterior seta and 1 posterior preapical seta. Mid tibia with 1 posterodorsal seta at mid-length, 1 anterodorsal seta beyond mid-length and 1 preapical dorsal seta; apex of circlet of 4–5 strongsetae.Hindfemurwithrowof4–6anterodorsalsetaeandseveralwidelyspacedanteroventraland posteroventralsetae.Hindtibiausuallywith2anterodorsaloneithersideofmid-length;1posterodorsal seta beyond mid-length; 1 dorsal preapical seta; 1 anteroventral apical seta. Wing (Fig. 41). Infuscate, with faint clouding about r-m and dm-m crossveins; veins dark; crossvein dm-m nearly at right angles, not aligned with M4; M4 beyond cell dm weakened to wing margin, onequarter length of crossvein dm-m; CuA+CuP weakened beyond basal third, reaching wing margin. Calypteres and halter yellow to orange. abdomen. Similar to thorax, brownish dorsally, with greyish pruinescence; with short dark setae, tergite 2 with longer setae. Sternite 4 rectangular with strong black lateral setae, nearly as long as sternite (Fig. 44). Sternite 5 broad, with pair of cylindrical lobes, curved medially; long setae on basal half of lobes (Fig. 45). Terminalia (Figs 45–46) (undissected): Epandrium rounded, narrow with long setae. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 327 Cercus long, narrow, apical margin rounded in lateral view; cerci closely approximated medially, with apical setae. Surstylus elongate with round apex; long wavy setae on apical half, longer than length of surstylus. Female Similar to male except, pedicel brown; without long pale setae on occiput, proboscis and fore coxa; tergite 7 subtriangular, fused anterolaterally with sternite 7, dorsally tapered and medially divided (Fig. 47); sternite 7 subtriangular, fused anterodorsally with tergite 7; tergite 8 U-shaped, enclosing proctiger, narrowly divided medially, obliquely angled; sternite 8 divided into pair of rounded digitiform lobes, directed dorsally and slender in dorsal view; epiproct and hypoproct small, triangular; cercus oval, thinly sclerotized (Fig. 47). Three spermathecae spherical, narrow and tapered posteriorly into duct (Figs 47–48). Distribution This species is recorded from Colorado and New Mexico (Fig. 62) and Utah (Vockeroth 1965), but specimens from the latter state were not located during this study. Acanthocnema torrenticola sp. nov. urn:lsid:zoobank.org:act:CD39CE73-763C-4174-8D51-C1CFC368A732 Figs 1–3, 49–60 Diagnosis This species is distinguished by the blackish ground colour, densely blue-grey pruinescent laterally, brown dorsally, palpus pale to dark brown in both sexes, orbital setae lateroclinate, fore tibia without row of short, black anteroventral setae and male sternite 5 without apical lobes. Etymology ThespecificepithetisderivedfromtheLatin‘torrens’(‘rushing’,‘rapid’),inreferencetothefastflowingstreams,creeksandriverswhereithasbeencollected. Material examined Holotype USA – Idaho • ♂; “USA: ID: Idaho Co. / Clearwater NF; Hwy 12 /Apgar Ck, 13.vi.2011 / N46°12′53.0″W115°32′13.6″ / B.J. Sinclair// CNC /905983 // HOLOTYPE / Acanthocnema / torrenticola / Sinclair [red label]”; CNC, CNC905983. Paratypes CANADA – Alberta •1♂;PeterLougheedPP,GrizzlyCk;50°45.890′N,115°8.379′W;1695ma.s.l.; 9 Jul. 2012; B.J. Sinclair leg.; forest and creek; CNC. – British Columbia •1♂,1♀;CathedralPP, Ashnola River; 49°08.13′N,120°02.12′W;750ma.s.l.;19Jul.2015;B.J.Sinclairleg.;CNC •1♂, 1♀;CowichanLake,HoneymoonBay;[48.818°N,124.172°W];6Jun.1955;G.E.Shewellleg.;CNC •1♀;Marysville,MarysvilleFalls,MarkCk;49°38.13′N,115°57.64′W;940ma.s.l.;16Jul.2015;B.J. Sinclair leg.; CNC •1♂;MtRevelstokeNP,GiantCedarTrail;[51.106°N,117.906°W];700ma.s.l.; 2 Jul. 1989; B.J. Sinclair leg.; cascading stream; CNC •1♀;Terrace,ElizaCk;[54.420°N,128.532°W]; 22Jun.1960;G.E.Shewellleg.;restingonblackflycage;CNC•1♂;samedataasforpreceding; 26 Jun. 1960; CNC •1♀;samedataasforpreceding;29Jun.1960;fromblackflycageinstream;CNC •1♂;samedataasforpreceding;13Jul.1960;cagetrapinstream;CNC•1♂;20mi.NofTerrace, KitsumkalumLake;[54.725°N,128.773°W];31May1960;G.E.Shewellleg.;CNC•1♂;49mi.W ofTerrace,SlickenslideCk;[54.211°N,129.603°W];9Jul.1960;J.G.Chillcottleg.;CNC•1♀;Perry European Journal of Taxonomy 1026: 304–337 (2025) 328 CreekFallsTrail;49°32.977′N,115°59.837′W;1095ma.s.l.;11Jun.2012;B.J.Sinclairleg.;cascading stream; CNC •1♂,2♀♀;WCreston,Hwy3,TopazCk;49°08.76′N,116°45.65′W;825ma.s.l.; 18 Jul. 2015; B.J. Sinclair leg.; CNC. – Ontario •1♂;CollingwoodTwsp,BlackAshCk;[44.494°N, 80.242°W];15May1948;F.P.Ideleg.;CNC•1♂;GreyCo.,Eugenia;[44.313°N,80.526°W];27Apr. 2008; S.A. Marshall leg.; DEBU •1♂;ForksoftheCreditPP,CreditR;43°48′49.60″N,80°0′56.95″W; 19 Jun. 2023; B.J. Sinclair leg.; CNC •1♀;HaltonCo.,LowvillePk,BronteCk;12May1990;B.J. Sinclair leg.; CNC •1♂,4♀♀;samedataasforpreceding;43°26′3.35″N,79°54′12.83″W;23Apr. 2023; CNC •1♂,2♀♀;WellingtonCo.,Fergus;[43.691°N,80.386°W];3Apr.2000;S.A.Marshall leg.; on rocks in river; DEBU •1♀;samedataasforpreceding;10.Sep.1995;DEBU•1♂,1♀(in copula),1♂;samedataasforpreceding;20Sep.1995;DEBU•1♂,1♀(incopula),2♂♂,2♀♀; same data as for preceding; Grand River; 2 Oct. 1995; DEBU •1♀;WellingtonCo.,Guelph,Speed R.atVictoriaRd;[43.588°N,80.273°W];1May1998;S.A.Marshallleg.;onrocksinriffle;DEBU. – Quebec •1♀;OldChelsea;[45.499°N,75.814°W];20Sep.1955,J.R.Vockerothleg.;CNC•1♂, 3♀♀;samedataasforpreceding;26Sep.1955;CNC•1♀;samedataasforpreceding;27Sep. 1955; KUMF. – Yukon •1♀;Whitehorse,LewesRiver;[60.391°N,134.833°W];24Jun.1949;L.R. Pickering leg.; CNC •1♂;samedataasforpreceding;30Jul.1949;CNC•1♂,1♀;samedataasfor preceding; 2 Jul. 1949; cage N.2; CNC •3♂♂,2♀♀;samedataasforpreceding;4Jul.1949;CNC •3♂♂;samedataasforpreceding;6Jul.1949;CNC•1♂;samedataasforpreceding;7Jul.1949; S.1; CNC •1♀;samedataasforpreceding;8Jul.1949;cageS.1;CNC•7♂♂,1♀;samedataasfor preceding; 9 Jul. 1949; CNC •1♀;samedataasforpreceding;KUMF•1♂;samedataasforpreceding; 13 Jul. 1949; cage S.2; CNC •1♀;samedataasforpreceding;19Jul.1949;S.2;CNC•1♀;samedata as for preceding; 22 Jul. 1949; CNC •2♂♂;samedataasforpreceding;27Jul.1949;cageN.2;CNC •1♀;samedataasforpreceding;29Jul.1949;cageN.2;CNC•1♂,1♀;samedataasforpreceding; 1–17 Aug. 1949; CNC •1♂;samedataasforpreceding;9Aug.1949;KUMF•1♂;samedataasfor preceding; mile 906; 9 Sep. 1949; cage S.5; CNC •1♂;samedataasforpreceding;31Aug.1949;CNC. USA – Alaska •1♂;mile14,RichardsonHwy;[61.067°N,145.905°W];HorsetailFalls;18Jul.1993; T. Saigusa leg.; KUMF •1♂,1♀;mile206,RichardsonHwy;[63°11′15″N,145°33′29″W];20Jul. 1987; M. Wood leg.; beaver pond; CNC. – California •1♀;ElDoradoCo.,SouthFkAmericanRiver, EagleRockriveraccess;38°46′34.6″N,120°16′00.7″W;18Jul.2012;J.M.Cummingleg.;CNC•1♀; MarinCo.,AlpineLake,LilyPond;[37.953°N,122.634°W];1500fta.s.l.;1–12Mar.1970;D.D. Munroe leg.; MT; CNC •1♂,1puparium;MarinCo.,MtTamalpaisSP,RedwoodCk,12mi.NofSan Francisco;37°52′N,122°34′W;20ma.s.l.;23Nov.2005;A.H.Purcellleg.;em.23–24Jan.2006; CNC •1♂;samedataasforpreceding;em.21Mar.2006;CNC•1♀,1puparium(inalc.);samedata as for preceding; em. 6 Feb. 2006; EMEC •1♂,1puparium(inalc.);samedataasforpreceding;em. 24 Feb. 2006; EMEC •1♀,1puparium(inalc.);samedataasforpreceding;em.24Feb.2006;EMEC •1♂,1puparium(inalc.);samedataasforpreceding;em.28Mar.2006;EMEC•1♀,1puparium (in alc.); same data as for preceding; em. 7 Apr. 2006; EMEC •1♀;NevadaCo.,ProsserCkatHwy 89;39°23′50.2″N,120°11′13.9″W;14Jul.2012;S.E.Brooksleg.;CNC.–Colorado •1♀;Archuleta Co.,Devil’sCk;37°12′58″N,107°17′41″W;6660fta.s.l.;17Jun.2017;J.M.Cummingleg.;CNC •1♂;BoulderCo.,So.St.VrainCk;[40°16′N,104°52′W];8Sep.1950;W.W.Wirthleg.;USNM. – Idaho •2♀♀;GoodingCo.,NiagaraSprings;[42.662°N,114.671°W];29Apr.1972;R.L.Newell leg.; CNC •1♂;samedataasforpreceding;30Jan.1973;R.L.NewellandD.S.Potterleg.;USNM •1♀;IdahoCo.,ClearwaterNF,Hwy12,3DevilsPicnicArea,2–3kmWofLowell;46°08.155′N, 115°38.681′W;450ma.s.l.;13Jun.2014;B.J.Sinclairleg.;smallstream;CNC•1♂,1♀;samedataas for holotype; CNC. – Maine •1♂,2♀♀;MtKatahdin,KatahdinFalls;[45.909°N,68.950°W];1600ft a.s.l.; 2 Jul. 1968; P. Ward leg.; CNC. – New Mexico •1♂;JamesSprings;[34.549°N,104.364°W]; 4 Jul. 1953; W.W. Wirth leg.; USNM. – Oregon •1♂,1♀;BentonCo.,AlseaFalls;44°19′31.70″N, 123°29′25.11″W;250ma.s.l.;5Jul.2014;J.M.Cummingleg.;CNC•1♂;HoodRiverCo.,2mi.E ofParkdale,EastFkHoodRiver;[45.530°N,121.578°W];11Jul.1989;B.J.Sinclairleg.;CNC•1♀; SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 335 7. Male palpus yellow (Fig. 13), dark in female; male sternite 5 divided into pair of divergent lobes (Fig. 18); fore tibia usually with 1 posteroventral seta near mid-length, 1 preapical posteroventral seta, slender, as long as basal width of fore femur and row of short, strong, black anteroventral setae proximal to ventral spur .............................................................................A. capillata (Loew, 1872) – Palpus pale to dark brown in both sexes (Figs 49–50); male sternite 5 not divided into pair of divergent lobes (Fig. 52); fore tibia with 0–1 posteroventral setae near mid-length, similar to ventral spur, without row of short, black anteroventral setae .................................... A. torrenticola sp. nov. Discussion There are now seven described and one undescribed species of Acanthocnema known from the Nearctic Region. In eastern North America, several species are sympatric, having been collected together in the same stream, i.e., A. albibarba, A. capillata and A. torrenticola sp. nov. Most specimens collected by the authorinthisstudywere‘sidecatches’duringattemptstocollectaquaticempidids(i.e.,Clinocerinae), consequently new records and species are likely to be discovered in the future through focussed surveys, especially west of the Appalachian Mountains, Midwestern United States and central Canada. In a world checklist, Bernasconi & Šifner (2021) listed A. glaucescens (Loew, 1864) from the Nearctic Region, but this remains doubtful especially since the source of this record could not be determined. Acknowledgements The following curators and collections kindly made specimens available for this study: Steve Paiero (DEBU), Peter Oboyski (EMEC), Karen Needham (UBCZ) and Allen Norrbom (USNM). 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In:McAlpineJ.F.,PetersonB.V.,ShewellG.E.,TeskeyH.J., Vockeroth J.R. & Wood D.M. (coords) Manual of Nearctic Diptera. Vol. 2: 1085–1097. Research Branch Monograph 28, Agriculture Canada, Ottawa. Zetterstedt J.W. 1846. Diptera Scandinaviae Disposita et Descripta. Tomus Quintus:1739–2162.Officina Lundbergiana, Lundae [Lund]. SINCLAIR B.J., Revision of Nearctic Acanthocnema (Diptera: Scathophagidae) 337 Printed versions of all papers are deposited in the libraries of three of the institutes that are members of the EJTconsortium:MuséumnationaldʼHistoirenaturelle,Paris,France;RoyalMuseumforCentral Africa, Tervuren, Belgium; Royal Belgian Institute of Natural Sciences, Brussels, Belgium. The other membersoftheconsortiumare:MeiseBotanicGarden,Meise,Belgium;NaturalHistoryMuseum of Denmark, Copenhagen, Denmark; Naturalis Biodiversity Center, Leiden, the Netherlands; Museo Nacional de Ciencias Naturales-CSIC, Madrid, Spain; Leibniz Institute for the Analysis of Biodiversity Change,Bonn–Hamburg,Germany;NationalMuseumoftheCzechRepublic,Prague,CzechRepublic; TheSteinhardtMuseumofNaturalHistory,TelAviv,Israël.