Schistostoma foliatum, Brooks, Scott E., Cumming, Jeffrey M. & Grimaldi, David A., 2019

Brooks, Scott E., Cumming, Jeffrey M. & Grimaldi, David A., 2019, Remarkable new fossil species of Schistostoma Becker (Diptera: Dolichopodidae Microphorinae) from mid-Cretaceous Burmese amber, Zootaxa 4624 (1), pp. 121-131 : 124-126

Schistostoma foliatum sp. nov.

( Figs 8–12 )

Type material. HOLOTYPE ♂, AMNH Bu-175, in Burmese amber with accompanying labels: “ AMBER: MYAN- MAR ( BURMA)/ Upper Cretaceous / Kachin: Tanai Village (on Ledo Rd. / 105 km NW Myitkyna)/ coll. Leeward Capitol Corp., 2000/ AMNH Bu-175”; “Burmese Amber/ DIPTERA :/ Microphoridae (raptorial male)*/ 1 ACA- RINA ”; “ HOLOTYPE / Schistostoma foliatum / Cumming, Brooks & Grimaldi [red label]”.

Diagnosis. This species is characterized by its enlarged lamellate apically acute fore tibia ( Fig. 8 ) with distinctive colouration pattern (lacking ‘eyespot’) and fringe-like marginal setae.

Description. Male. Body length 1.6 mm. Wing length 1.5 mm. Head: Elliptical in lateral view. Neck inserted near middle of head, with several short setae adjacent to occipital foramen. Ocellar triangle distinctly protruded with a pair of strong ocellar bristles and a pair of weaker postocellar setae. Holoptic (Fig. 10) with compound eyes contiguous for entire length of frons; compound eye ovoid in lateral view, occupying most of head, bare, dorsal ommatidia distinctly larger than ventral ommatidia, medial edge of eye with emargination slightly below level of antenna giving rise to demarcation line between larger dorsal and smaller ventral ommatidia. Frons entirely obliterated by eyes. Face and clypeus recessed in oral cavity. Face broad, subrectangular. Clypeus weakly bulging, mostly separated from frons, only connected medially by narrow sclerotized bridge. Occiput with series of 8–9 visible postocular setae per side. Gena narrow. Postgena broad. Antenna (Fig. 10) inserted near middle of head in profile; scape short about half length of pedicel; pedicel about 2X longer than wide than wide, with several setae; postpedi- cel strongly narrowing beyond basal third, with dorsal margin concave, about 3X longer than wide, clothed in fine hairs (longer ventrally); stylus arista-like, terminal, about 2.5X longer than postpedicel, 2-articled, basal article short. Palpus digitiform, with short setae. Proboscis narrow, directed anteroventrally, labellum with marginal setae. Thorax: Slightly longer than wide in dorsal view. Mesoscutum strongly arched (Fig. 10), prescutellar depression present. Proepisternum bare. Postpronotal lobe with 1 strong seta, with adjacent short seta. Acrostichal setae present, apparently biserial; other bristles of thorax well-differentiated, each side with: apparently 10–11 dorsocentrals, anterior dorsocentrals short and closely spaced, 2 posteriormost dorsocentrals strong and widely separated; several apparent strong supra-alar setae; 2 strong notopleural setae; 1 strong postalar seta. Scutellum with posterior margin rounded, with 2 pairs of setae, outer pair weak, inner pair strong. Mesopleuron apparently bare. Legs: Fairly long; foreleg and midleg with specialized morphology and chaetotaxy; tarsal claws, pulvilli and empodium normally developed on all legs. Foreleg ( Fig. 8 ): Coxa with a few short subapical setae visible; femur with several strong dorsal and dorsolateral setae, with large strongly projecting basiventral tubercle bearing 5 apical setae, ventral surface immediately distal to basiventral tubercle with series of about 6 short setae (not visibly borne on tubercles); tibia greatly enlarged and lamellate, leaf-shaped with apical margin acute, flattened laterally and very slightly concave medially, distinctly patterned ( Figs 8 , 12 ) but lacking discrete ‘eye spot’, lateral surface with longitudinal series of 5 short setae along middle and 6 longer setae basiventrally, dorsal and ventral margins with fringe of setae, medial surface bare; tarsus with short setae, tarsomere 1 as long as combined length of tarsomeres 2–3. Midleg ( Fig. 12 ): Coxa with strong elongate anterior seta at extreme base and series of 4 gradually shorter setae towards apex; trochanter with several weak setae; femur with strong elongate basidorsal seta, series of 3 strong anterodorsal setae along basal half (about half-length basidorsal seta), series of short dorsal setae towards apex, prominent basiventral tubercle bearing thick curved seta, 2 ventral setae near middle (of similar size) and several apparent anterior setae; tibia with flange on basal half bearing close-set series of short modified setae (some hook-shaped), 1 long erect anterior seta near mid-length, several hook-shaped setae on distal half; tarsomere 1 with setae somewhat longer than on tarsomeres 2–5. Hindleg: Coxal setae obscured from view; femur with series of strong dorsal and ventral setae of similar length, dorsal setae gradually shorter apically, ventral setae gradually shorter basally; tibia with series of strong dorsal setae, gradually stronger distally, series of similar ventral setae, gradually weaker distally; tarsomere 1 slightly shorter than combined length of tarsomeres 2–5, with prominent basiventral seta, otherwise with short setae similar to other tarsomeres. Wing: Pterostigma absent, membrane entirely covered with minute microtrichia ( Fig. 11 ). Anal lobe well-developed and right-angled, alula absent. Costa circumambient. Extreme anterior base of costa with 2 strong setae. Anterior costal section bearing row of short spine-like setae intermixed with fine setae from humeral crossvein to R 2+3, posterior part of costa beyond R 2+3 with only fine setae. Longitudinal veins complete reaching wing margin (CuA+CuP obscured from view). Sc faint apically. R 1 weakly sinuous, reaching costa beyond middle of wing (or beyond base of M 2). Base of Rs originating opposite humeral crossvein. R 2+3 diverging from R 4+5 apically. R 4+5 weakly sinuous. M 1 diverging from R 4+5 beyond cell dm. M 1 and M 2 strongly diverging beyond cell dm. M 2 and M 4 weakly diverging beyond cell dm. Short r-m crossvein present (but nearly indiscernible) in basal portion of wing, distal to base of R 4+5. Crossvein bm-m complete. Cell dm present, closed by base of M 2 and crossvein dm-m, cell extended to middle of wing. Cells br, bm and cua in basal fourth of wing. Cells bm and cua broader than br. Cell cua closed, rounded apically with CuA curved. Vein CuA+CuP obscured from view. Calypter obscured from view. Abdomen: Tergites and sternites 1–6 with relatively long setae. Segment 7 tubular, surface obscured from view. Sternite 8 ovoid, forming dome-like cap over dorsal region of hypopygium, with several strong marginal setae. Hypopygium ( Fig 7 ): Lateroflexed to right; inverted with posterior end directed anteriorly; small, about 1/5 length of abdomen, apparently symmetrical. Right and left epandrial lamellae rounded basally and oblong in ventral view, apices obscured from view. Hypandrium rounded basally with narrow elongate medial hypandrial process flanked by pair of strong setae. Cercus short, subtriangular, setose. Female: Unknown.

Etymology. The specific epithet refers to the greatly enlarged leaf-shaped tibia of the male foreleg.

Figures

FIGURES 5–8. Schistostoma burmanicum sp. nov. and Schistostoma foliatum sp. nov. 5. Right antenna of S. burmanicum, left medial view. 6. Left foreleg of S. burmanicum, left lateral view. 7. Hypopygium of S. burmanicum, ventral view. 8. Left foreleg of S. foliatum, left lateral view. Abbreviations: epand—epandrium; hypd—hypandrium; hypd proc—hypandrial process.

FIGURES 11–12. Schistostoma foliatum sp. nov. male holotype (AMNH Bu-175). 11. Wing. 12. Legs, right lateral view. Abbreviations: C—costal vein; CuA—anterior branch of cubital vein; cua—anterior cubital cell; dm—discal medial cell; dmm—discal medial crossvein; h–humeral crossvein; M 1, M 2, M 4 —medial veins; R 1, R 2+3, R 4+5 —radial veins; r-m—radial-medial crossvein; Sc—subcostal vein.