Six new species of Acomoptera from North America (Diptera, Mycetophilidae)

Abstract Six new species are described, raising the number of North American Acomoptera species to seven and the genus total to ten, and nearly doubling the number of species within the putative clade containing Acomoptera, Drepanocercus, and Paratinia. These novel species forms have implications for the concept of Acomoptera that in turn, may impact our understanding of its generic relationships and the evolution and composition of Gnoristinae and Sciophilinae. The new species, Acomoptera crispa, Acomoptera digitata, Acomoptera echinosa, Acomoptera forculata, Acomoptera nelsoni,and Acomoptera vockerothi, are compared with the type species of the genus, Acomoptera plexipus (Garrett), whose diagnostic features are imaged and illustrated for the first time. The European species, Acomoptera difficilis (Dziedzicki) is also illustrated and compared. Acomoptera spinistyla (Søli) comb. n. is transferred from Drepanocercus. A key to species is provided. Future work will seek to incorporate this knowledge into a systematic phylogenetic study of relationships between these species and their sister taxa.

evolution and composition of two large subfamilies of Mycetophilidae, the Gnoristinae and Sciophilinae.
Here, an additional six new species are described, raising the number of North American Acomoptera species to seven. These new species are compared with A. plexipus (Garrett), whose diagnostic features are imaged and illustrated. The European species, A. difficilis is also illustrated and compared. A key to species of the genus is included and apparent phylogenetic affiliations between congeners are briefly discussed.

Materials and methods
Terminology for wing venation generally follows , however interpretation of radial veins consistent with Søli (1997). Terminology for thoracic and genitalic morphology largely follows Wood (1991), , and . Terminology of thoracic sclerites and wing veins is standardized in Figs 7 and 8, respectively. Whole specimens and genitalia were macerated in 10% KOH at approx. 95°C for 15-20 minutes to remove soft tissue, then rinsed in distilled water and dilute glacial acetic acid, and dissected in water. All genitalia preparations were placed in a drop of DMHF and dry mounted onto a small card with transparent backing, held to the pin beneath the specimen. Illustrations and plates were made using Adobe Illustrator and Adobe Photoshop Creative Suite software, aided by digital images taken using a Q-imaging Micropublisher 5.0 scope-mounted digital camera. Habitus images were taken with the same digital camera, using an LED dome lighting system (Kerr et al. 2008). Material examined includes holdings deposited in the California State Collection of Arthropods, Sacramento, California, USA (CSCA); Canadian National Collection (CNC); California Academy of Sciences, San Francisco, California, USA (CASC); and the private collection of Olavi Kurina (Tartu, Estonia). Paratypes are also deposited in 100% EtOH in the Frozen Tissue Collection of the CSCA (CSCA-FTC) at -80°C for DNA preservation. Specific collection holding and deposition information is provided in the species accounts. High resolution images of studied material are deposited and publicly available in Morphbank (http://www.morphbank.net/). Morphbank image numbers are cited within brackets, in the figure captions, and serve as embedded links. taxonomy Acomoptera Vockeroth http://species-id.net/wiki/Acomoptera Acomoptera Vockeroth, 1980: 534 Type species. Eudicrana plexipus Garrett, 1925: 4, by subsequent designation. Diagnosis. This genus may be distinguished from most mycetophilid genera by the following combination of wing characters: Sc ending in C, sc-r present near middle of Sc, and R4 present and displaced from Rs by more than 2.5× its own length. Acomoptera may be distinguished from Paratinia by having wing membrane bare and from Drepanocercus by having the cubital fork near the level or distad of sc-r. Acomoptera is distinguished from Phoenikiella Chandler by having a setose Sc, with sc-r positioned near the middle of this vein.
Description. Body length 4.5 to 7.1 mm. Ocelli three, subequal or median ocellus reduced, lateral ocellus separated from eye margin by approximately its own diameter or clearly less. Eye with a broad distinct emargination above antennal base, with microsetae usually scattered and short, but sometimes more numerous and longer. Frons bare between ocelli and antennal bases. Frontal tubercle present. Antenna two to four times as long as thorax, 2/3rds to approximately same length as abdomen; antennal bases nearly touching, separated only by narrow tip of frontal tubercle; all flagellomeres densely setulose, elongate, flagellomere length decreases gradually toward tip. Palpus with five palpomeres; palpomere 1 short, as wide as long, remaining palpomeres longer than wide (except sometimes palpomere 2 as wide as long); palpomere 2 clearly shorter than or subequal to palpomere 3; palpomere 4 three to six times longer than wide; palpomere 5 thinner than others, six to eleven times longer than wide, usually subequal to combined length of palpomeres 3 and 4. Scutum with short appressed acrostichal and dorsocentral setae and longer and more erect sublateral setae, the intervening areas bare. Scutellum with three or four irregular rows of short to long setae, sometimes bare medially. Paratergite present; antepronotum with setae on posterior half, proepisternum bare; mesopleuron, metapleuron, and prosternum bare; metanotum with one to three erect setae laterad of base of halter; mediotergite and laterotergite bare; phragma not well developed. Wing unmarked, with dense microtrichia, without macrotrichia. Costal vein extends beyond R 5 , between approx. 0.25× and 0.33× distance between R 5 and M 1 ; sc-r crossvein present, slightly distad of middle of Sc, proximal of Rs; R4 present (when missing, teratogenic), located approx. 3× its own length from Rs, forming an elongate radial cell; medial fork approx. 3× longer than stem; cubital fork arises near level or distad of sc-r and proximad of medial fork, cubital stem shorter than CuA 1 and approx. equal in length to or longer than CuA 2 ; all cross veins bare on upper surface, all longitudinal veins setose on upper surface, except CuP and the first two sections of M bare (as an exception, A. crispa sp. n. may have a few setae on M 1+2 ); wing veins R 1 , R 5 , M 1 , and sometimes M 2 with at least some setae on lower surface. Hind coxa with a single vertical row of setae on at least proximal half (sometimes weak). Tibial bristles short but distinct, the longest between half and full tibial diameter in length. Anteroapical depressed area of fore tibia ovate and well developed. Tibial spur pairs of equal length, hind tibial spurs usually longer than mid tibial spurs, but sometimes mid and hind spurs subequal in length. Tarsal claws each with one or two small ventral teeth. Empodia small. Sternite 1 bare. Sternites 2 to 7 each with a pair of broad, poorly defined, submedian to sub lateral fold-lines. Terminalia not rotated. Epandrium (tergite 9) between three times as wide as long to slightly wider than long. Hypandrium (sternite 9) fused with gonocoxites, the synsclerite with or without a narrow transverse membranous area across ventral surface, with or without a ventral preapical hook-like process directed posteriorly. Gonostylus variously formed, often divided into two or three lobes. Posterodorsal process attached to the median dorsal angles of the gonocoxites variously shaped, sometimes arising as a distinctive bilobed wing-like structure whose posterior margins are darkened and toothed. Cerci broad, flat, broadly rounded apically, with fine setae. Hypoproct broad, semicircular, weakened anteromedially.
Female sternite 8 deeply emarginate posteriorly, the rest of the median area membranous or lightly sclerotized. Sternite 9 with two weakly sclerotized anterolateral areas and two slender, more heavily sclerotized submedian processes projecting posteriorly. Tergite 10 short, setose, fused on either side with sternite 10. Sternite 10 well developed, membranous medially, tapering on posterior half, posterior margin extending to apex of first segment of cercus. Cercus 2-segmented, first segment almost twice as long as wide, second segment oval.
Key to the Acomoptera of the world (males)  fig. 1, Søli, 1993: fig. 1); hypandrium with unsclerotized area near posterior margin (Søli, 1993: fig. 2B  Diagnosis. This species is most similar to A. vockerothi in having similarly-shaped gonostyli that feature a line of long, curved setae near the dorsal margin. Acomoptera crispa may be separated from A. vockerothi by the gonocoxites lacking a posteromedial denticulate ridge ventrally (Fig. 2B, 3B). It is also distinguished by having a longer, narrower ventromedial gonostylus lobe, which is usually forked (Fig. 3E) and the outer dorsal lobe is broadly attached laterally (Figs 2D, 3D-E).
Description. Male. Body length: 6.0 mm. Wing length: 5.8 mm. Coloration (Fig. 1). Head light brown; palpomeres yellow to yellowish brown. Antennal scape and pedicel yellow to yellowish brown, flagellomeres yellowish increasingly yellowish brown toward tip. Thorax yellowish brown; area of scutum bearing acrostichal and dorsocentral setae defined by darker coloration, scutum setae gold-or golden brown-colored. Mid leg becoming increasingly brown towards tarsi; coxae yellowish or cream-colored; femur yellowish, tibia yellowish brown, tarsi brown (other legs missing, but likely having similar coloration). Wing hyaline without markings, wing veins yellowish brown; haltere stem and knob yellow to light yellowish brown. Abdominal segments concolorous, yellowish brown, with scattered yellow and brown setae. Terminalia yellowish brown. Head. Ocelli slightly raised; middle ocellus approx. same size as lateral ocelli; lateral ocellus located approx. width of ocellus or less from eye margin, separated from median ocellus by approx. twice its own diameter. Eyes with sparse, inconspicuous microsetae, which are approximately as long as width of facet. Antennal length probably approx. 4.0 mm (approx. 0.8× length of abdomen). Palpus approx. 1.0-1.25× width of head (anterior view); length of palpomeres 2 and 3 subequal; palpomere 4 approx. 4.5× longer than wide; palpomere 5 approx. 10× longer than wide, subequal to or longer than combined length of palpomeres 3 and 4.
Female unknown. Etymology. The species epithet "crispa" is an adjective meaning curly in Latin, and refers to the long curved setae of the gonostylus.

Acomoptera difficilis (Dziedzicki)
http://species-id.net/wiki/Acomoptera_difficilis Diagnosis. This species may be distinguished from all other Acomoptera species by the dorsoventrally elongate suboval shape of the gonostylus, which features a prominent, finger-like lobe that projects inward (Fig. 11D) and a ventral, posterior-protruding lip that bears an elongate, narrow process (Figs 11D-E).
Head. Ocelli slightly raised; middle ocellus smaller or about the same size as lateral ocelli; lateral ocellus located approx. its own width (approx. width of two eye facets) from eye margin, separated from median ocellus by 2-3× its own diameter. Eyes with sparse, inconspicuous microsetae, which are approximately as long as width of facet. Face with brown setae, longest of which approx. same length as width of face. Antennal length approx. 0.75× length of abdomen. Palpus shorter than width of head (anterior view); palpomere 2 clearly shorter than palpomere 3; palpomere 4 approx. 3× longer than wide; palpomere 5 approx. 6× longer than wide, shorter than combined length of palpomeres 3 and 4. Thorax (Fig. 7). Antepronotum bearing setae; remaining thoracic sclerites bare. Tarsal claw usually with two small ventral teeth. Wing venation as in Fig. 8; costal vein extends beyond R 5 , approx. 0.25× distance between R 5 and M 1 ; R 1 , R 5 , and M 1 with at least some setae on lower surface.
As male in all aspects except the following: Generally moderately darker than male (Fig. 6B). Antennal scape brown, pedicel and flagellomeres light brown, yellowish brown, or brown. Scutum setae black. Legs becoming increasingly brown towards tarsi, coxae light brown (coxal setae black); fore femur yellowish or cream-colored, mid and hind femora light brown or brown; tibia and tarsi brown to light brown. Wing membrane darker and wing veins stronger than in male; abdominal setae black. Terminalia yellowish or yellowish light brown, form as in Fig. 9.
Comment. The female specimen was united with males on the basis of similar coloration patterns (e.g., bicolored mediotergite) and having been collected with males at a locality known only for this species.
Etymology. The species epithet "digitata" is an adjective derived from the Latin word for finger, referring to the adaxial process of the gonostylus.   Diagnosis. This species is similar to A. nelsoni sp. n. in that the male gonocoxites display a prominent dorsomedial comb (Fig. 14A) and the outer surface of the gonostyli bear denticulations (Figs 14B, 14D). The gonostyli of both species are also similar in that the dorsoapical margin comes to an acute point and is darker in color than the rest of the gonostylus (Fig. 14D). The gonostyli of A. echinosa sp. n., however, lack denticulations on the inner surface of the gonostyli dorsally (Figs 13A, 14A).
Coloration (Fig. 12). Head brown; palpomeres light brown. Antennal scape light brown, pedicel yellowish, base of first flagellomere yellowish, otherwise flagellomeres between R 5 and M 1 ; R 1 , R 5 , and M 1 with at least some setae on lower surface (ventral M 2 sometimes with setae, also).
Female unknown. Etymology. The species epithet "echinosa" is an adjective derived from the Greek word meaning hedgehog or sea-urchin, referring to the spiny surface of the gonostylus. brown. Thorax cream-colored to brown; scutum brown to dark brown; dorsocentral areas of scutum defined by lighter brown coloration, scutum setae gold-or golden brown-colored; laterotergite and mediotergite light brown to cream-colored. Legs becoming increasingly brown towards tarsi, coxae cream-colored; femur yellowish or cream-colored, tibia yellowish brown to brown, tarsi brown. Wing hyaline without markings, wing veins light brown; haltere stem and knob cream-colored to light brown. Abdominal segments concolorous, brown, slightly darker posteriorly, with golden brown setae. Terminalia yellowish brown to brown.
Head. Ocelli slightly raised; middle ocellus clearly smaller than (approx. 0.25× size of ) lateral ocelli, lateral ocellus located approx. width of ocellus or less from eye margin, separated from median ocellus by approx. twice its own diameter or a little more. Eyes with sparse, inconspicuous microsetae, which are approximately as long as width of facet. Face with golden brown setae, longest of which approx. same length as width of face. Antenna and abdomen subequal in length. Palpus approx. 1× width of head (anterior view); length of palpomeres 2 and 3 nearly subequal (palpomere 3 longer); palpomere 4 approx. 6× longer than wide; palpomere 5 approx. 11× longer than wide, subequal to or shorter than combined length of palpomeres 3 and 4.
Thorax. Antepronotum bearing setae; remaining thoracic sclerites bare. Tarsal claw usually with one small ventral tooth. Wing venation similar to others in the genus (e.g., A. digitata sp. n., Fig. 8  Diagnosis. This species is unique in the genus for having a forked hypandrial lobe (Fig. 16D). The form of the gonostylus (Fig. 17D) is reminiscent of that displayed by A. difficilis (Fig. 5D), but the posterior-projecting ventrolateral process is significantly shorter (Fig. 17E). Coloration (Fig. 15). Head brown; palpomeres yellowish light brown. Antennal scape brown, pedicel yellowish light brown, base of first flagellomere yellowish light brown, remaining flagellomeres slightly darker. Thorax mostly brown; scutum uniformly brown to dark brown and/or area of acrostichal setae darkened, areas laterad of dorsocentral setae with darker brown markings, scutum setae gold-or golden brown-colored; laterotergite and mediotergite light brown to brown. Legs darkening towards tarsi (although in some cases, hind legs less so), coxae yellowish or cream-colored; femur yellowish light brown, tibia and tarsi light brown to brown. Wing hyaline without markings, wing veins light brown; haltere stem and knob cream-colored to light brown. Abdominal tergites 2-5 brown, with posterior margins yellowish or cream-colored; other segments concolorous brown; abdomen with golden brown setae. Terminalia yellowish brown to brown.
Female unknown. Etymology. The species epithet "forculata" is an arbitrary combination of letters alluding to the prominently forked hypandrial lobe. Diagnosis. The male gonopods of A. nelsoni sp. n. are similar to A. echinosa sp. n., as noted above. The gonostyli of A. nelsoni, however, are unique in having denticulations arranged in rows, which are present on the inner surface of the gonostyli dorsally (Fig. 20A), in addition to the profile of its form in both dorsal and ventral views (Figs 19A-B, 20A-B). The gonocoxal dorsomedial comb is also unique, in being swept back and more narrow than in other Acomoptera species that have this structure (Fig. 20A).
Head. Ocelli slightly raised; middle ocellus clearly smaller than (approx. .25× size of ) lateral ocelli, lateral ocellus located approx. width of ocellus or less from eye margin, separated from median ocellus by approx. twice its own diameter. Eyes with sparse, inconspicuous microsetae, which are approximately as long as width of facet. Face with mostly brown setae, longest of which approx. same length as width of face. Antenna and abdomen elongate (probably) subequal in length. Palpus approx. 1× width of head (anterior view); palpomere 2 clearly shorter than palpomere 3; palpomere 4 approx. 6× longer than wide; palpomere 5 approx. 11× longer than wide, subequal to or shorter than combined length of palpomeres 3 and 4.
Coloration (Fig. 21). Head brown; palpomeres yellowish darkening to brown distally or brown throughout. Antennal scape and pedicel brown; base of first flagel- lomere yellowish, otherwise flagellomeres brown. Thorax mostly brown, with some lighter areas (e.g., mediotergite); scutum brown to dark brown; darker in areas of acrostichal and dorsocentral setae, scutum setae gold-or golden brown-colored. Legs becoming increasingly brown towards tarsi, coxae cream-colored; femur yellowish or cream-colored, tibia yellowish brown to brown, tarsi brown; hind legs lighter in color. Wing hyaline without markings, wing veins brown; haltere cream-colored to light brown. Abdominal segments concolorous brown, with predominantly light, golden setae. Terminalia mostly brown, except gonostyli yellowish.  Head. Ocelli slightly raised; middle ocellus approximately same size as lateral ocelli, lateral ocellus located approx. width of ocellus or slightly less from eye margin, separated from median ocellus by approx. twice its own diameter. Eyes with numerous microsetae, longest approx. twice as long as width of facet. Face with mostly brown setae, longest of which approx. same length as width of face. Antenna approximately 2/3rds length of abdomen. Palpus approx. 1× width of head (anterior view); palpomere 2 short, as wide as long, remaining palpomeres longer than wide; palpomere 4 approx. 4× longer than wide; palpomere 5 approx. 7× longer than wide, subequal to or shorter than combined length of palpomeres 3 and 4.
Thorax. Antepronotum bearing setae; remaining thoracic sclerites bare. Wing venation similar to others in the genus (e.g., A. digitata sp. n., Fig. 8), may exhibit teratological variations (e.g., loss of R 4 ( Fig. 21; in this specimen, R 4 lost on left wing but present on right wing)); costal vein extends beyond R 5 , approx. 0.3× distance between R 5 and M 1 ; R 1 , R 5 , and M 1 with at least some setae on lower surface.

Acomoptera sinica Wu & Yang, 1990
Acomoptera sinica Wu & Yang, 1990: 276 Comment. Specimens of this species were unavailable for examination. The crude illustrations in the original publication show this species having genitalia that are significantly different from known Acomoptera and the description lacks critical additional information. For this reason, the proper generic placement of this species has not been confirmed. Acomoptera spinistyla (Søli, 1993) Drepanocercus was originally defined on the basis of having the cubital fork very near the base of the wing and elongated female cerci (Vockeroth, 1980). Acomoptera spinistyla shows neither of these features and in its original placement, prevents a clear distinction between Drepanocercus and Acomoptera. The spiky gonostyli of D. spinistylus recall similar conditions found in Acomoptera species such as A. digitata (Fig. 11D) and A. plexipus (Fig. 23D). Furthermore, in A. spinistyla and A. plexipus, there is a bifurcate dorsomedial process (Søli, 1993: fig. 2D, Fig. 23A) and a broad gap before the posterior margin of the hypandrium (Søli, 1993: fig. 2B, Fig. 23B). For these reasons, it seems appropriate that this species be transferred to Acomoptera. Further study is needed to evaluate the position of Drepanocercus ensifer; for now, it remains separated from Acomoptera by its original defining characters.  Diagnosis. This species is most similar to A. crispa sp. n. in having similarly-shaped gonostyli that feature a line of long, curved setae near the dorsal margin, as mentioned above. The gonocoxites of A. vockerothi bears a posteromedial denticulate ridge ventrally, however (Figs 25B, 26B). It is also distinguished by having a short, unforked ventromedial gonostylus lobe (Fig. 26E) and the outer dorsal lobe is broadly attached dorsally (Figs 25, 26A-B, 26D-E).
Coloration (Fig. 24). Head brown; palpomeres yellow to yellowish brown. Antennal scape, pedicel, and flagellomeres yellow to yellowish brown, flagellomeres darker than scape and pedicel. Thorax cream-colored to yellowish or light brown; area of scutum bearing acrostichal and dorsocentral setae defined by darker coloration, scutum setae gold-or golden brown-colored. Legs becoming increasingly brown towards tarsi, coxae yellowish or cream-colored; femur yellowish, tibia yellowish brown, tarsi brown. Wing hyaline without markings, wing veins brown; haltere stem and knob yellow to light yellowish brown. Abdominal segments concolorous, yellowish brown to brown, with scattered yellow or golden brown setae. Terminalia yellowish brown.
Head. Ocelli slightly raised; middle ocellus approx. same size as lateral ocelli; lateral ocellus located approx. width of ocellus or less from eye margin, separated from median ocellus by approx. twice its own diameter. Eyes with sparse, inconspicuous microsetae, which are approximately as long as width of facet. Face with brown setae, longest of which approx. same length as width of face. Antennal length approx. 0.8× length of abdomen. Palpus approx. 1.0-1.25× width of head (anterior view); length of palpomeres 2 and 3 subequal; palpomere 4 approx. 4.5× longer than wide; palpomere 5 approx. 10× longer than wide, subequal to or longer than combined length of palpomeres 3 and 4.
Male Genitalia (Figs 25-26). Epandrium approx. 3× wider than long. Gonocoxites with dorsomedial comb (Figs 26A). Gonostylus complex, as shown in Figs 25, 26A-B, 25D-E.  Female unknown. Etymology. The species is named after J.R. Vockeroth, a remarkably friendly and engaging person, legendary figure in the history of Dipterology, author of the genus, and frequent collector of this species.

Discussion
Hypotheses of relationship among Acomoptera species were not explicitly tested, however shared features of the male genitalia suggest self-evident affiliations. The shared presence of a well-developed dorsomedial gonocoxal comb is an important feature for uniting A. crispa, A. echinosa, A. nelsoni, and A. vockerothi (Figs 2A, 11A, 19A, 25A). All of these species are described for the first time here, and represent a newly-recognized lineage within the genus. Within this group, A. crispa and A. vockerothi exhibit exceptionally similar morphologies of the gonostylus. Overlap in gonostylus form also suggests a close relationship between A. echinosa and A. nelsoni.
A second group appears composed of A. forculata, A. plexipus, and the European species, A. difficilis. These species have a hypandrial lobe in the form of an apical hook or fork and a three-part gonostylus bearing a marginal lobe, whose similarity is especially noticeable when viewed from the lateral perspective (Figs 5E,17E,23E). Within this group, the dorsomedial structure of the gonocoxites in A. difficilis and A. forculata is developed in much the same way (Figs 5A, 17A), suggesting a close relationship between these taxa. The position of A. digitata remains unclear.
In light of this newly expanded Acomoptera concept, boundaries of sister taxa may be revisited, particularly those of Drepanocercus. Chandler (1999) asserted that A. spinistyla is an intermediate between the type species of Drepanocercus (D. ensifer (Garrett 1925)) and Acomoptera, based on the intermediate position of the cubital fork. The position of this fork is obscured in some specimens due to the base of CuA 1 either being weak or obsolete (e.g., Søli 1993: fig. 1), as it is in D. ensifer (e.g., Vockeroth 1980: fig. 6). Ševčík (2004) notes, however, that there is variation in this character in A. spinistyla and frequently, specimens have CuA 1 complete, with a clear attachment point to CuA 2 . In such specimens, the fork is approximately at the level of sc-r, just proximad of r-m (Ševčík 2004: fig. 1). The phylogenetic significance of the position of the cubital fork remains unknown in this and other mycetophilid groups, such as in Tetragoneura Winnertz and its relatives. For now, however, Drepanocercus remains defined on the basis of having the cubital fork very near the base of the wing and elongated female cerci (Vockeroth 1980). Given the expanded morphological diversity now known to exist within Acomoptera, the generic relationships may be addressed in a more comprehensive manner, particularly with respect to Paratinia and Drepanocercus, and their relation to established members of Gnoristinae and Sciophilinae. This will be the topic of future phylogenetic study.
(Estonian University of Life Sciences; Tartu, Estonia) for loan of specimens critical to this study. Edward Coher, Peter Chandler, and one anonymous reviewer provided very helpful comments on an earlier version of this manuscript. Rosser Garrison and Megan O'Donnell graciously provided illustration advice. Thank you also to Li Shi, who kindly provided a translation of Wu and Yang (1990).