Megatrigon Johnson 1898
Creators: name: Doczkal, Dieter
name: Radenković, Snežana
name: Lyneborg, Leif
name: Pape, Thomas
Publisher: name: Zenodo
Year: 2016
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Insecta
Diptera
Syrphidae
Megatrigon

description: Megatrigon Johnson, 1898: 159 stat. nov. (resurrected as a valid genus from the synonymy with Eumerus Meigen, 1822).
Originally included species
Megatrigon sexfasciatus Johnson, 1898.
Type species
Megatrigon sexfasciatus Johnson, 1898 (holotype, ♀ (BMNH), examined), by original designation.
Remarks
The holotype is without the posteroventral patch of setae on katepisternum. This is quite unusual among Megatrigon and all other Merodontini (currently only known from Lyneborgimyia magnifica Doczkal & Pape, 2009) and probably this is an individual aberration (the number of posteroventral katepisternal setae is very low – usually less than 10 – in most Megatrigon, lower than usually seen in the Merodontini). In all other characters this specimen fits the diagnosis of Megatrigon given below. The male of Megatrigon sexfasciatus is unknown (probably not present in the available material).
Diagnosis
With all autapomorphies of the Merodontini (Doczkal & Pape 2009; as Eumerini) except for the colour of the pterostigma, which is clear in most species. Unique characters (autapomorphies) within Merodontini are:
1) lower calypter setose dorsally,
2) metafemur posterodorsally on proximal half obliquely striate (Fig. 6 A–B),
3) stem vein R without setae (if exceptionally one or a few setae are present then they are no longer than 0.5 × the width of the vein),
4) tergite 1 laterally (lateral to the apex of metepimeron) bare,
5) tergite 2 anterolaterally with a large triangular bare area (Fig. 9A),
6) hamus characteristically S-shaped (Fig. 11N:x),
7) subepandrial sclerite with long microtrichia (Figs 10B:w, 13C–D, G:z).
Description
HEAD. Lateral corners of mouth edge well developed, anterior edge of mouth slightly produced (except for Megatrigon jacobi (Hervé-Bazin, 1913) comb. nov.), dorsal part of face more or less distinctly convex below antenna, median part of lunula extended posteriorly (similar to Merodon), both dorsal and ventral part of post-ocular orbit wide, post-ocular ridge present, postcranial carina absent, dichoptic (Fig. 2), eye setose, without enlarged ommatidia in ♂. Fossette ill-defined, in a lateral position, postpedicel without longitudinal furrows, arista simple. Clypeus slender, postclypeus well sclerotized, labellum elongated (as in many Merodon).
THORAX. Notopleural sulcus absent, notal wing process of Eumerus - type, supra-alar bristles well developed, their alveoli enlarged, scutal alveoli with raised margins, post-alar callus nearly entirely setose, scutellum> 2 × as wide as long, its marginal rim yellow, scutellum with concave ventral surface, without ventral fringe, probasisternum large, approaching proepisternum, proepimeron moderately extended ventrally [as in Eumerus tricolor (Fabricius, 1798)], katepimeron almost flat, katatergite with a weak carina, metepisternum bare.
WING (Fig. 5). Cross-vein sc-r well developed, C ending far before apex of wing, R 4+5 moderately sinuous (as in Eumerus tricolor), M 1 without stump veins, dm-cu almost perpendicular to CuA 1, usually with stump vein, CuA 1 slightly more than 2 x as long as dm-cu, bm-cu about as long as basal part of CuA 1 or slightly longer, CuA about 3 x as long as CuA 2, A 1 +CuA 2 smoothly curved, Cup short and ending at about half length of CuA, wing broad, about 2.35 × as long as wide, wing margin with undulated membrane, costagium with long setae at posterior margin (except in Megatrigon nivalis), marginal fringe of upper calypter ‘glued’ (cf. fig. 32I–K in Hippa & Ståhls 2005).
LEGS. Procoxa short and stout, mesocoxa posteriorly usually bare (except for M. jacobi comb. nov.); metafemur shiny, thickened and curved dorsally, about 2.5 × as long as deep, light yellow setae on metafemur exceed relatively large apical flange, usually with shiny, bare, longitudinal area ventrally; ventral face of metafemur slightly convex or straight, with a low anteroventral preapical flange bearing weak bristles on strong finger-like outgrowths, and with a few weak bristles posteroventrally preapically (Fig. 6C); metatibia with a sharp bare (a few isolated setae may occur) anteroventral ridge in proximal half, protibia with irregularly spaced anterolateral apical setae; protarsus short and stout, tarsomeres 2–4 as wide as long; claws enlarged.
ABDOMEN. Tergites strongly curved ventrally at margin; anterior corners of tergite 2 inflated, border between tergites 1 and 2 not crenulated; lateral margins of tergites microtrichiose; ♂ sternite 4 without projections, with incised posterior margin and a fine desclerotised median line, lateral margins simple, sternite 6 bare, sternite 7 with a basal bump. Anterior surstyle lobe absent, posterior surstyle lobe narrow (Fig. 13A, E:y), subepandrial sclerite microtrichiose (Fig. 13 C–D, G:z). Setae on various part of the body serrated (Fig. 9B), except in M. nivalis comb. nov. The included species can be arranged into three well defined species groups, each defined by several autapomorphic character states.
description: Published as part of Doczkal, Dieter, Radenković, Snežana, Lyneborg, Leif & Pape, Thomas, 2016, Taxonomic revision of the Afrotropical genus Megatrigon Johnson, 1898 (Diptera: Syrphidae), pp. 1-36 in European Journal of Taxonomy 238 on pages 3-4, DOI: 10.5852/ejt.2016.238, http://zenodo.org/record/3849874