Schistostoma burmanicum, 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 : 122-123

Schistostoma burmanicum sp. nov.

( Figs 1–7 )

Type material. HOLOTYPE ♂, AMNH Bu-0029, in Burmese amber with accompanying labels: “ AMBER: MYANMAR (BURMA)/ Upper Cretaceous?/ Kachin: Tanai Village (on Ledo Rd. / 105 km NW Myitkyna)/ coll. Leeward Capitol Corp., 1999/ AMNH Bu-0029”; “Burmese amber/ DIPTERA :/ ♂ Microphorinae :/ (raptorial)”; “ HOLOTYPE / Schistostoma burmanicum / Cumming, Brooks & Grimaldi [red label]”.

Diagnosis. This species is characterized by its enlarged lamellate apically truncate fore tibia ( Fig. 6 ) with distinctive ‘eye spot’ and laminate setae along upper ventral margin.

Description. Male. Body length 1.8 mm. Wing length 1.4 mm. Head: Apparently more or less elliptical in lateral view, but compound eyes, occiput and postgena collapsed. Neck inserted apparently below middle of head, with several short setae adjacent to occipital foramen. Ocellar triangle distinctly protruded with a pair of strong ocellar setae and a pair of weaker postocellar setae. Holoptic with compound eyes contiguous for most of 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 small, triangular, mostly obliterated by eyes. Face and clypeus recessed in oral cavity and obscured from view. Occiput with series of 3–4 visible postocular setae. Gena obscured from view but apparently very narrow. Postgena broad. Antenna ( Fig. 5 ) inserted near middle of head in profile; scape obscured from view, apparently short; pedicel about 2X longer than wide, with several setae; postpedicel elongate subtriangular, about 2.5X longer than wide, clothed in fine hairs; stylus arista-like, terminal, about 2X longer than postpedicel, 2-articled, basal article short. Palpus obscured from view. Proboscis narrow, directed anteroventrally. Thorax: Slightly longer than wide in dorsal view. Mesoscutum strongly arched, prescutellar depression present. Proepisternum bare. Postpronotal lobe with 1 strong seta. Acrostichal setae present, apparently biserial; other bristles of thorax well-differentiated, each side with: approximately 9 dorsocentrals, anterior dorsocentrals short and closely spaced, 2 posteriormost dorsocentrals strong and widely separated; 3 apparent 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 ( Figs 4 , 6 ): Coxa without visible setae; femur with series of 4 visible strong dorsolateral setae, with large basiventral tubercle bearing 4 apical setae, ventral surface immediately distal to basiventral tubercle with series of 7 short setae, each borne on a tiny tubercle; tibia greatly enlarged and lamellate with apical margin truncate, flattened laterally and slightly concave medially, distinctly patterned with ‘eye spot’ on apical third, lateral surface with short setae along dorsal margin as well as two longitudinal series of short setae near middle and adjacent to ventral margin, ventral margin adorned with modified laminate, thickened and curved setae, medial surface with series of short setae along apical margin, otherwise bare; tarsus with short setae, tarsomere 1 as long as combined length of tarsomeres 2–4. Midleg: Coxa with strong elongate anterior seta at extreme base and smaller seta immediately below, two weak anterior setae near middle; trochanter with several weak setae; femur with strong basidorsal seta, series of 4 similarly strong anterodorsal setae along basal half, series of short dorsal setae running towards apex, prominent basiventral tubercle bearing thick curved seta and 2 ventral setae near middle (distal seta weaker); 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; tarsomere 1 as long as combined length of tarsomeres 2–5, with series of erect setae dorsally, otherwise with short setae similar to other tarsomeres. Hindleg: Coxa with 1 strong lateral seta at basal third, 2 gradually smaller setae apically, several weak apical setae along anterior margin; femur with series of strong dorsal and ventral setae, ventral setae longer; tibia with series of strong dorsal setae, series of weaker ventral setae along basal half; tarsomere 1 as long as combined length of tarsomeres 2–5, with series of stronger setae dorsally, otherwise with short setae similar to other tarsomeres. Wing: Pterostigma absent, membrane entirely covered with minute microtrichia. Anal lobe obscured from view. 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 (except CuA+CuP) complete, reaching wing margin. Sc faint apically. R 1 reaching costa beyond middle of wing (or beyond base of M 2). Base of Rs obscured from view. 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 in basal portion of wing, distal to base of R 4+5. Crossvein bm-m apparently 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, partially obscured from view. Cell cua apparently closed, rounded apically with CuA curved. Vein CuA+CuP apparently present and short. Calypter obscured from view. Abdomen: Tergites and sternites 1–6 with short setae. Segment 7 tubular, with 1 weak seta visible on sternite. Sternite 8 subrectangular, 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 posterior view, each with pair of narrow subequal apical epandrial lobes, cluster of short setae dorsally near base of epandrial lobes, otherwise bare. Hypandrium rounded basally with narrow elongate medial hypandrial process flanked by pair of strong setae. Cercus obscured from view. Female: Unknown.

Etymology. The specific epithet refers to Burma, source of the amber.

Remarks. The specimen has clusters of small spheres near the legs ( Figs 2 , 6 ), which could be spores, very small pollen grains, or brochosomes (see Suludere et al. 2018) that will require higher magnification to ascertain.

Figures

FIGURES 1–2. Schistostoma burmanicum sp. nov. male holotype (AMNH Bu-0029). 1. Habitus photograph, left lateral view. 2. Habitus illustration, left lateral view.

FIGURES 3–4. Schistostoma burmanicum sp. nov. male holotype (AMNH Bu-0029). 3. Habitus photograph, right lateral view. 4. Right foreleg and midleg, right lateral view.

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.