Mysteromyia plumosa, Grimaldi, 2016

Grimaldi, David A., 2016, Diverse Orthorrhaphan Flies (Insecta: Diptera: Brachycera) In Amber From The Cretaceous Of Myanmar: Brachycera In Cretaceous Amber, Part Vii David A. Grimaldi, Bulletin of the American Museum of Natural History 2016 (408), pp. 1-132 : 82-85

Mysteromyia plumosa , new species

Figures 28 , 29 , 60

DIAGNOSIS: As for genus, by monotypy.

DESCRIPTION: Based on female. Body length 3.48 mm; head width 1.06 mm, head length 0.38

mm; thorax width 0.67 mm, thorax length 0.79 mm; abdomen length 2.27 mm; wing length 2.00 mm. Head: Broad (due to broadened frons and facial area), distance between inner margins of eyes slightly greater than 2× frontal width of eyes; width of head greater than greatest width of thorax. Head cuticle brown, appears finely wrinkled (probably preservational). Eyes bulging, with very fine, sparse setulae; no differentiation of facets (e.g., frontally or dorsoventrally). Eye semicircular in lateral view, occiput very exposed; height of eye occupies entire dorsoventral height of head. Inner frontal margin of eye gently emarginate at level slightly above antennae. Head devoid of macrosetae. Ocelli absent, though anterior one possibly present as porelike vestige near center of frons; frons with fine vertical line between central pore and face. Frons and frontoorbital plate well defined by suture. No lunule/ ptilinal suture present above antennal bases. Face very small, with very small triangular clypeus between antennal bases. Antenna: Bases separated by width equal to diameter of scape. Scape and pedicel very short, ringlike. Flagellum: Flagellomere 1 thickest antennal article, bulbous, asymmetrical, setulose, with small nipplelike lobe on anteroapical margin; flagellomere 2 small, asymmetrical, situated at apex of flagellomere 1 (vs. dorsally); flagellomere 3 a plumose “arista” with long, dense, dorsal and ventral branches, with ca. 20 dorsal and 20 ventral branches, longest branches at base (lengths ca. 0.5× length of aristal trunk), branches tapered in length apicad; base of each branch socketed. Gena slightly bulbous, setulose. Mouthparts: Proboscis and palps completely absent, mouth present as small figure-eight-shaped pit on head venter, with 2 small sclerites within. Occiput bulging, central portion of occiput concave, to which cervical area is attached. Thorax: Slightly longer than broad, no macrosetae. Dorsally: Mostly light brown, virtually bare, with very sparse setulae/microsetae in small areas. Postpronotal lobes small, widely separated. Anterior part of scutum with 3 large, oblong, high tubercles/calli, an anteromedian one and two postero- paramedian ones. Transverse suture very short, virtually longitudinal (not transverse); supraalar lobe expanded into pointed lobe in dorsal view. Dorsum of thorax flattened, such that scutellum situated almost entirely dorsally. Scutellum pentagonal in shape; no proscutellum; postnotum broad, fully exposed dorsally. Ventrally: extensively membranous. Ventral cervical sclerite long, slender, isolated in membrane. Anepisternum bulging laterad. Proepisternum a small, narrow sclerite, prosternum a small, central sclerite. Area between procoxae and proepisterna broadly membranous. Katepisternum small, anterior portion membranous. Meso- and metasternites small, surrounded by extensive membrane, as is medial-ventral surface of mesocoxa. Wing: Ovoid, with dramatically costalized radial veins; membrane and veins posterior to costalized veins very faint. Wing W/L 0.35. Costa without spinules; Sc complete, long, 0.48× length of wing; R 1 meets C immediately after apex of Sc; C+R 1 ends 0.80× length of wing along anterior margin, where apex of R 2+3 meets C+R 1; Rs extremely short. C, Sc, R 1, Rs, R 2+3, and basal crossveins r-m and m-cu tubular and sclerotized; C+R and R 2+3 thickest and most heavily sclerotized. Membrane without microtrichia, except for faint, minute microtrichia in basal veins M, cup, Sc, and R. Veins R 4+5, M, CuA 1, CuA 2 +A 1, and A 2 extremely faint, not tubular or sclerotized, simple (unforked). R 4+5 basally incomplete; CuA 2 +A 1 and A 2 apically incomplete. Alula and upper calypter well developed; lower calypter not present. Legs: Slender, darker brown than rest of body. No macrosetae; no tibial spurs. Coxae well developed, ones in each pair well separated; mesocoxa and metacoxa with ventromedial surfaces membranous; no metacoxal pegs. Profemur equal to length of protibia; meso- and metafemur shorter than meso- and metatibia. Tibiae with apical, semicirclet of stiff microsetae; tarsi long, basitarsomeres longer than remaining (distal) tarsomeres combined. Claws well developed, empodium setiform and minute; pulvilli small, slender lobes. Abdomen (female): Slender, longer than head and thorax combined. Tergites brown, virtually glabrous. Tergite 1 highly reduced, a very narrow transverse band/strap; tergite 2 larger, largest tergite is 3; tergite 6 longest; tergite 7 short, tergite 8 small, slightly reniform; tergite 9 apparently lacking; tergite 10 a small, slender sclerite. Presence/absence of abdominal muscle plaques uncertain. Sternites lost, venter of abdomen completely membranous. Male Terminalia: Unknown. Female Terminalia: Segment 10 membranous, apical margin with minute spines (acanthophorite spines?); cerci fused, 1-segmented.

TYPE: Holotype, female, JZC Bu-1817a.

ETYMOLOGY: In reference to the plumose structure of the apical antennal article.

COMMENTS: With the exception perhaps of certain apterous, inquiline Phoridae , Mysteromyia is one of the most remarkable flies I’ve seen, living or extinct. A host of highly derived features make this an unmistakable taxon: the plumose “arista” (with socketed branches), loss of mouthparts, loss of abdominal sternites, reduction in thoracic sternites; the extreme, phoridlike costalization of the wing; and the three large scutal tubercles (similar to what is seen in Trichoptera). This fly is definitely not a Cyclorrhaphan but may be an eremoneuran.

The fly was embedded within a cabochen originally 21 × 13 × 8 mm, along with the remains of an orthopteran (head, antennae), a beautifully preserved alate termite ( Kalotermitidae ), an empidoid fly, and a Collembolan. The piece was sectioned into four pieces, with the fly in a cubed section 6 × 7 × 3 mm, along with a pselaphid beetle. The fly is complete and beautifully preserved.

Figures

FIG. 28. Mysteromyia plumosa, new genus and species (Mysteromyiidae, new family), holotype JZC Bu-1817a. A. Wing, dorsal surface. B. Frontal portion of head, with antennae, dorsofrontal view. C. Head, frontal view. D. Female terminalia, dorsal view.

FIG. 29. Mysteromyia plumosa, JZC Bu-1817a. Ventral view of head and thorax, showing loss of mouthparts and significant reduction of ventral sclerites.

FIG. 60. Mysteromyia plumosa, new genus and species (Mysteromyiidae, new family), holotype JZC Bu-1817a. A. Habitus, ventral. B. Terminalia, ventral. C. Terminalia, dorsal. D. Head and thorax, dorsal, showing tubercles. E. Head and thorax, ventral. F. Right wing.