Tapantiomyia enigmatica, Michelsen, 2017

Michelsen, Verner, 2017, Tapantiomyia enigmatica, new genus and species proposed for a stilt-legged and otherwise bizarre coenosiine fly (Diptera: Muscidae) from Costa Rica, Zootaxa 4277 (4), pp. 583-590 : 584-589

Tapantiomyia enigmatica sp. nov.

( Figs 1‒5 , 6‒8 , 9‒15 )

Etymology. The specific name refers to the strange morphology of the wings and legs finding no matches among other known Muscidae .

Description. Male. Measurements (n = 1): Body length = 3.9 mm; wing length = 4.5 mm; fore femur = 2.4 mm; mid femur = 3.5 mm; hind femur = 3.4 mm; fore tibia = 2.1 mm; mid tibia = 3.1 mm; hind tibia = 2.9 mm; fore tarsus = 1.6 mm; mid tarsus = 1.7 mm; hind tarsus = 1.7 mm.

Colour. Ground colour of head, including antennae, palpi and prementum, brownish black. Head velvety dark brown pruinose on frontal vitta, occiput and genae; following parts in contrast silvery white pruinose: median upper occiput including ocellar tubercle, fronto-orbital plates beyond pair of orbital setae, parafacialia and a large blotch on postgenae; face, apart from upper part of facial ridges, shiny white with a golden hue. Even antennal pedicel medially silvery white pruinose. Prementum glossy, devoid of pruinescence. Thorax ( Figs 1, 2 ) brownish black with blotches of silvery white pruinescence on postpronotal calli, on posterior corners of prescutum and on upper posterior part of anepisternum; mesonotum darkly subshining through thin layer of golden and brownish pruinescence delimiting two broad, darker stripes at level of dorsocentral setal rows; lower parts of pleura whitish grey pruinose. Wing bases and calypteres faintly ochre-brown tinged; knob of halteres cream coloured. Legs brownish black except brightly ochre-yellow on trochanteres and narrow basal parts of mid and hind femora; fore coxae densely yellowish white pruinose. Abdomen ( Figs 7, 8 ) brownish black; all tergites dorsally with a strong dark shine through sparse layer of brown pruinescence; tergites II‒V laterally with prominent patches of silvery white dusting; sternites I‒V light grey pruinose, exposed and widely separated from tergites by pleural membrane.

Head ( Figs 1‒3 ). Fully dichoptic; eyes bare; width of frons in dorsal aspect 1.3x width of one eye. Frontal vitta without setae or setulae, much wider than fronto-orbital plates, but gradually narrowing towards lunule; ocellar triangle narrow, extended to ptilinal suture. Fronto-orbital plates well demarcated by colour in upper orbital and lower frontal sections, the former with only 1 reclinate pair of orbital setae and a few setulae, the latter with only 1 inclinate pair of frontal setae. Ocellar tubercle with a weak pair of proclinate ocellar setae followed by two pairs of setulae; inner vertical setae relatively strong, outer vertical setae absent; distinct pair of convergent paravertical setae present; supracervical setulae seemingly absent. Upper occiput bare apart from lax row of uniform postocular setae; postgenae on upper part with black setae, on lower part with yellowish setae and setulae; genae bare apart from a few yellowish setae on posterior part. Facial ridges notably dilated downwards, only beset with a short vibrissal seta and a few subvibrissal setulae. Antennae: Antennal sockets very close-set, not separated by a facial carina; scape short, with a few fine setulae at dorsal margin; pedicel with a distinct longitudinal seam; postpedicel less than twice as long as pedicel; 1st aristomere not visible in situ, either extremely short or absent; 2nd aristomere no longer than its diameter; 3rd aristomere thickened and very short-pubescent on basal part, becoming very thin and totally bare on distal two-thirds. Mouthparts: Palpi relatively long, slender, bearing short setae and setulae, including some yellowish ones on basal part. Haustellum ( Fig. 4 ) slightly shorter than palpi, with strongly sclerotized, apically tapering prementum bearing only a few setulae; labella small; prestomal teeth enlarged and pointed, clearly adapted for stabbing live prey.

Thorax ( Figs 1, 2 ). Anterior spiracle small with brownish fringes; posterior spiracle small with cream coloured fringes. Postpronotal lobe with one seta and a few fine setulae only. Notopleuron bare apart from two unequal setae. Acrostichals not differentiated from fine ground setulae on scutum; dorsocentral setae 1+3, but first two postsutural setae short and fine, almost setulose; posthumeral, prealar and intraalar setae absent. Scutellum, apart from fine setulae on dorsal part, only with a subbasal and a longer, crossed apical pair of setae. Prosternum bare, narrowing on anterior fourth. Proepisternum bare apart from one fine dark seta; proepimeron with one pale seta and some pale setulae, a few of them curved antero-ventrally. Anepisternum, apart from some scattered pale setulae, only with three dark setae in hind marginal row. Katepisternum, apart from scattered pale setulae on upper and posterior parts, with one short, pale upper anterior seta and one long, dark upper posterior seta. Anepimeron and meron bare; katepimeron (barette) with a single pale setula. Metapleural parts bare.

Wing ( Figs 1 , 6 ). Long, slender, anal lobe weakly developed, hence broadest part of wing lies beyond middle. Vein C between humeral and subcostal breaks distinctly inflated and with a single anterior row of fine pale setulae; subcostal break lies well beyond point where vein Sc terminates in vein C; vein C distal to subcostal break with usual upper and lower anterior rows of alternating spinules and setulae, otherwise bare on surfaces above, between and below these rows. Remaining wing veins without setulae. Vein R4+5 and M1 widest apart at mid length between cross-vein m‒cu and wing margin, distinctly converging on subdistal part but parallel on distal part. Cell cup smaller than cell bm; vein A1 + CuA2 very short, fading out almost immediately. Upper calypter short, semicircular, with a fringe of very long ciliae being pale on lower two thirds and dark on upper third; lower calypter reduced, forming a narrow, linear fold.

Legs ( Figs 1, 5 ). Femora and tibiae extremely long and slender, see under Measurements. Tarsomere 1 about as long as combined length of tarsomeres 2‒5; claws and pulvilli short. Leg chaetotaxy overall very short; ground setulae sparse and nowhere arranged in distinct rows, of yellowish colour on coxae, trochanters and extreme bases of femora. Main setae coarser than ground setulae but very few exceed greatest diameter of fore femur. Fore femur with av and pv setal rows on distal 2/3; subapically with 1 ad and 1 pd seta. Mid femur with av and pv setal rows on distal 4/5, an entire row of a‒ad setae, some pd setae on middle 1/3, and subapically with 1 ad, 1 pd and 1 p setae. Hind femur with av and pv setal rows on distal 2/3, an entire row of ad setae, a pd setal row on distal 2/3, and subapically with 1 ad and 1 pd seta. Fore tibia with 3 d setae situated 1/5 from base, at mid-length and subapically respectively, and with apical pv seta. Mid tibia with 3‒ 4 v ‒pv setae on more than distal half, 4 pd setae on more than basal half, and apically with 1 pd, 1 p, 1 pv and 1 av setae. Hind tibia with 4 av setae, 3 ad setae, and 0‒1 pd seta near base, subapically with 1 d seta and apically with 1 av seta. Hind tarsomere 1 without v seta near base.

Abdomen ( Figs 7‒9 ). Short, ovoid, dorsal sclerites invisible between tergite V and epandrium. Setosity overall short and fine, pale yellowish on sternites II‒V and ventro-lateral parts of tergites I‒V. Sternite I bare; sternite V cordiform, membranized along shallow hind marginal incision; setae and setulae largely confined to posterior lobes; tergite VI and dorsal part of asymmetrical pregenital sclerite fused and forming a narrow arch concealed under tergite V and bearing a single pair of setulae only. Abdominal spiracles I‒VII in respect to size and position in agreement with the typical pattern of a muscid fly.

Terminalia ( Figs 10‒15 ). Epandrium large but divided mid-dorsally. Proctiger field enlarged; anus flanked by a pair of prominent plates (paraprocts?). Cerci forming an anchor shaped plate, narrowly incised on projecting apical part; median fusion seam maintained. Surstyli of typical muscid shape. Hypandrial plate subvertical, moderately extended, not tubular, on top seamlessly supporting a pair of pregonites. Postgonites slightly longer than pregonites, with a few sensilla and weakly sclerotized on apical part. Rod-like phallapodeme connected to combined posteromedial extensions of pregonites. Sclerite of sperm pump cup-shaped, without apodeme. Basiphallus with bell-shaped epiphallus; distiphallus short, simply tubular, extensively membranized on distal part.

Female. Unknown.

Type material examined. COSTA RICA: Prov. Cartago: Paraíso: P.N. Tapantí, 9.720N, 83.774W, 1600m. Malaise trap, ZADBI-331. Holotype ♂, 2-9.xii.2012 (Projecto ZADBI, INBio #105651 ). The holotype is in excellent condition, glued onto a pointed piece of cardboard mounted on an insect pin. The abdomen was removed and dissected after treatment in 10% potassium hydroxyde; the dissected parts are stored in glycerol in a microtube attached to the pin bearing the specimen.

Distribution. Neotropical; known only by the male holotype from Costa Rica.

Biology. Nothing is known. The type locality lies in tropical cloud forest at 1600m. The structure of the mouthparts with small labella and enlarged prestomal teeth suggests that Tapantiomyia enigmatica adults are capable of hunting live prey such as small, soft-cuticular Diptera . This has been documented for many coenosiine Muscidae and may represent a basic habit of the subfamily.

Figures

FIGURES 1 ‒ 5. Tapantiomyia enigmatica sp. nov., male holotype. 1. Lateral view, abdomen removed. 2. Same, dorsal view. 3. Head, anterior view. 4. Haustellum and labella; notice strong prestomal teeth. 5. Legs, anterior view.

FIGURES 6 ‒ 8. Tapantiomyia enigmatica sp. nov., male holotype. 6. Ventral view of wing base. 7. Abdomen, lateral view. 8. Same, latero-ventral view.

FIGURES 9 ‒ 15. Tapantiomyia enigmatica sp. nov., male holotype. 9. Sternites I ‒ V and pregenital sclerites. 10, 11. Hypopygium, posterior and left lateral views. 12. Genital structures, left lateral view. 13, 14. Same after removal of phallus, left lateral and posterior views. 15. Phallus, left lateral view. Same scale for Figs 10 ‒ 15. Abbreviations: ba, basiphallus; di, distiphallus; ej, ecaculatory sclerite; ep, epiphallus; hy, hypandrium; pa, phallapodeme; pog, postgonite; prg, pregonite; StV, sternite V.