Zhenia xiai

Grimaldi, David A. & Barden, Phillip, 2016, The Mesozoic Family Eremochaetidae (Diptera: Brachycera) in Burmese amber and Relationships of Archisargoidea: Brachycera in Cretaceous Amber, Part VIII, American Museum Novitates 2016 (3865), pp. 1-32 : 4-10

Zhenia xiai Q.-Q. Zhang et al.

Figures 1–4 , 6C

DIAGNOSIS: Same as for genus, by monotypy.

REDESCRIPTION: Features that are not mentioned in the original description (Q.-Q. Zhang et al., 2016), or that are corrected and revised here are indicated in italics.

Body slender, gracile; head large, thorax compact; legs and abdomen long and slender; most of body light, yellowish, with dark brown markings dorsally on thorax and on abdominal tergites and sternites. HEAD: Large, subcircular in frontal view, compressed anteroposteriad. Eyes dark, very large, occupying almost entire dorsal, ventral, and frontal surfaces of head, no genal area exposed; posterior margin of eye entire (not emarginate); eye bare, no setulae; facets differentiated: group of ca. 50 large facets in middle of frontal surface, remaining facets ≤0.5 × diameter of frontal facets. Eyes holoptic in female (presumably also in male, probably more so), inner margins meeting from just above clypeus to just below antennal insertions. Antennal sockets not separated, fused into one. Antenna: Small, flagellum aristalike, pedicel slightly cone shaped, with apical setulae; postpedicel with base drop shaped, finely setulose, extended apically into long, fine, bare, aristalike structure with minute apical stylus; postpedicel base 0.2× length of entire postpedicel. Frons narrow and short, width less than distance between posterior ocelli; frons slightly longer than ocellar triangle; ocellar triangle raised into low tubercle, darkly pigmented; ocelli well developed. Face exposed as very narrow isosceles triangle, slightly swollen near middle. Mouthparts present: labrum exposed, 0.075 mm W × 0.25 L, slender apical margin with notch. Maxillary palps very small, 1-segmented, setulose, light in color. Labellum well developed, laterally compressed, with ≥ 25 pseudotracheae, apical margin with fringe of fine setulae. Postocciput darkly pigmented, with low median ridge between ocellar triangle and occipital foramen; protruding collar just above occipital foramen, large posterior tentorial pit on each side of occipital foramen.

THORAX: Short, compact, 0.16× body length, with well-preserved color pattern: most of scutum, all of scutellum and mediotergite dark brown; scutum with broad, median, lighter stripe; mediotergite with darker central and lateral spots; posterior surface of metacoxa and most of halter knob dark brown; all other portions of thorax (pleura, legs, etc.) light, yellowish. Pleural sclerites as illustrated (fig. 4).

WING: Slender, petiolate, veins dark brown, but membrane with no pigmentation, and entirely covered with fine, dense microtrichia. Vein C tapered toward apex, ends at wing tip just before tip of M 1+2. Short, incomplete crossvein h slightly distal to level of arculus; faint sc-r 1 crossvein present. Sc complete, long, 0.65× length of entire wing. R 1 with setulae on upper surface; Rs stem very short, situated in middle of R 1; apex of R 2+3 fused to R 1 well before apex of R 1. Stem of R 4+5 fused to base of M 1+2; apical fork of R 4+5 very small, asymmetrical (R 4 ca. 0.5× length of R 5). Apices of R 4-5 and M 1 nearly encompassing wing tip; M 3 lacking. Cell dm with 6 irregular sides, veins forming proximal and distal sides weak in middle (probably a line of flexion through middle of cell dm). Stem of M between cells br and bm well formed; cell br slightly longer than bm. No m cell present. CuA 2 fused to A 1 just before wing margin (cup cell closed). Anal lobe essentially absent, alula absent; vein A 2 present but short and incomplete, within petiole of wing; wing with narrow base, petiolate. LEGS: Long and slender, without spines or macrosetae; tibiae without apical spurs. Coxae: procoxa slender, meso and metacoxa ca. 0.6× length of procoxa; trochanters well developed, slender. Metafemur 1.8× length of profemur; metatibia 1.8× length of protibia; metatarsus 1.5× length of protarsus; length of metabasitarsomere equal to combined length of distal four metatarsomeres; length of probasitarsomere 0.35× combined length of four distal protarsomeres. All distitarsomeres dorsally with apical notch and pair of smaller lateral notches. Pretarsus with minute, short, highly vestigial claws (largely hidden under distitarsomere); pulvilli and empodium developed into extremely long pads, 0.5 mm L × 0.1 mm W (propretarsus), 0.4 mm L × 0.1 mm W (metapretarsus). Empodium and pulvillar pads with fine, dense scales laterally, striations medially.

ABDOMEN: Long and slender, cylindrical, comprising 0.75 length of entire body, greatest thickness of abdomen 0.45 mm (segment VII). Abdomen mostly yellowish, with dark brown, short transverse bands on tergites and sternites of segments I–VI near anterior margin of each sclerite (segments VII and VIII entirely yellowish); band on tergite and sternite of each segment contiguous. Lengths of abdominal segments (relative to VIII, the shortest segment): I 1.2: II 1.9: III 2.0: IV 1.9: V 1.6: VI 1.6: VII 1.1: VIII 1.0. No macrosetae present, only dense, fine, decumbent setulae. Each tergite overlapping dorsal margins of corresponding sternite. Spiracle positions (in membrane/sclerite) not observed. Tergite 8 with posterior margin produced into ventrolateral lobes. Terminus produced into sclerotized, glabrous, aculeate oviscapt 0.70 mm length, with dorsal and ventral grooves (paired valves), which are the cerci; dorsal to the oviscapt is a small, setulose sclerite (or pair). Male terminalia unknown.

MATERIAL EXAMINED: Female, AMNH Bu-SD2, Department of Invertebrate Zoology, AMNH. Specimen in 99 myo amber (Late Albian–Early Cenomanian) from Kachin Province, northern Myanmar, outcrops ca. 20 km SW of the village of Tanai. Preservation of fly is excellent, with color patterns beautifully preserved. The only portions missing are metatarsi and right mesotarsus; antenna detached but lying close to fly (one antenna is above fly’s head, other under the right pretarsus, both floating free).

COMMENTS: Zhenia has myriad specialized features; the ones shared with other families of Brachycera that seem important for discerning relationships are discussed below (Discussion). Here we review the autapomorphic features of Zhenia .

The very dorsal attachment of the antennae near the ocelli appears to be a synapomorphy for Archisargoidea . Because the antennae of the AMNH specimen are detached, the antennal attachment sites are exposed, revealing that the sockets are entirely fused into one. Antennal sockets can be contiguous in some orthorrhaphans, and even partially fused, but no fly to our knowledge possesses a single, fully fused socket as in Zhenia . The antennal flagellum of the fossil is also distinctive, being single-articled and styluslike, with a microscopic stylus at the tip. The only orthorrhaphan group with a single-articled flagellum is Acroceridae . Large eyes that are holoptic or nearly so in both sexes is another archisargoid feature. The enlarged frontal facets is an unusual feature found, for example, in some Asilidae , particularly forest-dwelling genera. This feature strongly suggests that Zhenia had excellent frontal resolution, likely used for spotting hosts.

The most distinctive aspects regard the pretarsus: extremely vestigial claws and very large, elongate pretarsal lobes. The pulvillae of Zhenia were originally interpreted as enlarged pretarsal claws (Q.-Q. Zhang et al., 2016), but the fine structure of the pulvillae and empodium (also called the mediolobus) are identical, leaving no doubt about the identity of the paired structures. The pretarsal claws are, in fact, minute structures not extending beyond the distal margin of the distitarsomere. Vestigial pretarsal claws of Zhenia appear to be an autapomorphy within the Archisargoidea since well-developed claws have been reported in at least 12 other genera of archisargoids ( Grimaldi and Cumming, 1999; Grimaldi and Arillo, 2008; Grimaldi et al., 2011; Mostovski, 1996a; Nartshuk, 1996; Ren and Guo, 1995; Ren, 1998; J.-F. Zhang, 2012a, 2014a; K.-Y. Zhang et al., 2010a). Virtual loss of the claws is probably related to the enormous development of the pulvilli and empodium. Large to very large empodia (none the size in Zhenia ) are found in some Recent families of flies, such as many Asilidae , most Pipunculidae , and Stylogaster (Conopidae) . These taxa are either predators or they are parasitoids that inject eggs into their hosts.

A pointed, piercing oviscapt is functionally convergent in various Brachycera that oviposit either by piercing plants (various Tephritoidea and Nerioidea), or piercing arthropod hosts ( Pipunculidae , Stylogaster , some Phoridae [e.g., Apocephalus ], Pyrgotidae , and some Tachinidae ). Given the structure of the eyes and pretarsi, it is most likely that Zhenia used its oviscapt as a parasitoid, as was previously concluded (Q.-Q. Zhang et al., 2016).

Figures

FIGURE 1. Photomicrographs of Zhenia xiai, AMNH BuSD-2. A. Right lateral habitus. B. Head and thorax, dorsolateral view. C. Head, ventrolateral view

FIGURE 2. Photomicrographs of Zhenia xiai, AMNH Bu-SD2. A. Right wing. B. Detached antenna. C. Left mesotarsus. D. Right protarsus. E. Terminalia (female), dorsolateral view. F. Terminalia, ventral view.

FIGURE 3. Illustrations of important details of Zhenia xiai, based directly on AMNH Bu-SD2. A. Front of head, showing enlarged frontal facets, face and mouthparts. B. Frons, showing fused antennal sockets. C. Detached antenna, with minute apical style. D. Female terminalia; the cerci are modified into a piercing structure. E. Pretarsus, showing the enormous development of the empodium and pulvillae, and the minute claws.

FIGURE 4. Reconstructed habitus of Zhenia xiai. The posture with its abdomen curled under is conjectural, based on the habits of various living flies with similar piercing oviscapts. Color patterns are entirely as preserved.

FIGURE 6. Wings of exemplar Archisargoidea, redrawn from original sources. Not to scale.