Chirosiomima Hennig, 1966

Michelsen, Verner, 2014, Taxonomic assessment of Chirosiomima Hennig (Diptera: Anthomyiidae), with proposal of a new genus for Hylemyia curtigena Ringdahl, Zootaxa 3790 (1), pp. 86-102 : 87-88

Genus Chirosiomima Hennig, 1966

( Figs. 1–3 , 4–9 , 10–12 , 13, 14 )

Chirosiomima Hennig 1966: 29 . Type species now fixed (under Article 70.3 of the Code) as Pegomyia obscurinervis Emden, 1941 , misidentified as Hylemyia gestroi Séguy, 1930 in the original designation by Hennig (1966).

Description. Size. Very small to small anthomyiids; wing length 2.5–4.5mm.

Colour. Ground colour of head, body and appendages very variable, ranging from specimens with extensively ochre yellow head, body and appendages (except for a round, brown or blackish mark on upper part of parafacials), to specimens with wholly darkened body, posterior part of head, distal part of postpedicel and fore femur. Head, prementum and body covered in pale grey dusting revealing no darker pattern on dorsum of thorax and abdomen except for a pair of vague brown dorsocentral stripes on scutum. Calypteres white, halter ochre yellow. Wing slightly tinged with ochre brown, sometimes narrowly brownish infuscated at cross-veins r–m and dm–cu.

Male. ( Fig. 1 ). Head: Fully feminized; outer and inner vertical setae strong; upper occiput bare behind short postocular setae; broad frons with frontal vitta about 3 times as wide as each parafrontal, with a pair of interfrontal setae; each parafrontal with two reclinate and one proclinate orbital setae followed by one inclinate frontal seta. Fronto-parafacial angle prominent, in profile view reaching well beyond lower margin of face; parafacial strongly narrowing downwards, in the middle about half as wide as postpedicel. Gena broad, in lateral view about 1.5 times as broad as postpedicel, bare except for a few setae in a single row. Postpedicel about 2 times as long as broad; arista short, basally rather thickened, aristal pubescence much shorter than greatest basal diameter of arista. Proboscis short with small labella and numerous small, bicuspid teeth ( Fig. 2 ); palpus slender.

Thorax: Acrostichals no stronger than surrounding ground setulae, in rows standing closer to each other than to dorsocentral rows and without setulae between rows. Prealar seta much shorter than posterior notopleural seta, often no stronger than adjacent ground setulae. Proepisternals 1 seta and 1 setula; proepimerals 1 seta and 1 setula. Anepisternum without setae in upper anterior corner. Katepisternals 1 + 1. Lower calypter much shorter than upper calypter, forming a shallow lobe.

Wings: Vein C with a row of v setulae on more than basal two-thirds. Cross-vein dm–cu straight and upright.

Legs: Fore tibia with ad seta, without p or pv seta, apically only with d seta and pv seta. Mid femur with 0–1 av and 1–2 pv setae near base; mid tibia with 1 ad and 1–2 pd setae. Hind femur with 3–5 av setae on distal two-thirds and 1–2 pv setae on basal half; hind tibia with 1 av, 3 ad and 2 pd setae, without any p or pv setae, apically without pd seta but with pv seta.

Abdomen: Short, subcylindrical. Tergites III–V with weak marginal setae, tergite V also with short discal setae. Tergite VI bare. Sternite IV not longer than wide. Sternite V with posterior lobes mesally expanded on distal part ( Figs. 4 , 10 ); surstyli slender, narrowly incised at apex ( Figs. 5–7 , 11 ); pregonites with two robust apical setae, laterobasally fused with hind margin of hypandrium; postgonites much shorter and weaker than pregonites and bare apart from a few sensilla ( Fig. 8 ). Short distiphallus laterally fused with large basiphallus into an anvil-shaped structure ( Fig. 9 ); small epiphallus supported by a vertical sclerite uniting the hypandrial arms behind phallus ( Fig. 8 ); usual articulation between hypandrial arms and surstyli abandoned due to absence of bacilliform sclerites.

Female. ( Fig. 3 ). Almost indiscernible from the male apart from the structure of the terminalia. Oviscapt ( Figs. 12–14 ) rather short and thick; spiracles VI and VII moved forward, situated about middle of tergite VI; sternite VI enlarged and convex; tergites VII and VIII devoid of usual hind marginal setae and setulae; tergite VII split into a pair of widely separated plates firmly aligned with sternite VII laterally and with tergite VIII dorsally; sternite VII pieces forming pointed extensions at lateral hind corners.

Monophyly and relationships of Chirosiomima Hennig. As presently defined, the genus Chirosiomima Hennig includes only two species, the Southern Mediterranean C. gestroi (Séguy) and the Northern Afrotropical and South Asian C. obscurinervis (Emden) .

After exclusion of the species C. collini Ackland and C. curtigena (Ringdahl) , the genus is homogenous and monophyletic beyond reasonable doubt. Affirmative evidence is found in the structure of the terminalia. Female: sternite V enlarged and convex; tergites VII and VIII devoid of hind marginal setae and setulae; tergite VII split into a pair of widely separated plates transposed beneath tergite VIII and closely aligned with lateral margins of sternite VII. Male: pregonites much larger than postgonites and firmly attached to central plate of the hypandrium; postgonites inconspicuous and twisted, bare apart from a few sensilla; phallus of very peculiar anvil-shape with a poorly differentiated distiphallus; articulation between hypandrium and surstyli abandoned in the absence of bacilliform sclerites.

Hennig (1976b: lix) commented on the status and possible relationships of Chirosiomima , but his definition of the genus was probably polyphyletic by inclusion of the species collini Ackland and curtigena Ringdahl. As presently defined, morphology may suggest a possible closest relationship between Chirosiomima and Fucellia Robineau-Desvoidy , though the evidence at hand is far from persuasive. The latter genus consists of 22 littoral species, most of them found in seashore habitats of the Northern Hemisphere. The monophyly of Fucellia is well supported by the following autapomorphies: presence of a submarginal row of spaced setal spines on ventral surface of vein C; epiphallus reduced, replaced by a vertical sclerotized strut articulated with basiphallus; 6th pair of spiracles in the female displaced forward from hind corners of tergite VI to membranous “intersegmental” section of segment VI or even further forward to tergite V. Both genera contain “terrestrial” species in which the male head is fully feminized, and both sexes have small eyes, broad genae, reduced lower calypteres, and usual hair-like setulae missing beneath tip of scutellum. Males of both genera agree in the following: cerci forming a short and broad, shield-like plate beneath an enlarged proctiger field.

Biology. Virtually nothing is known. Material of Chirosiomima is remarkably scarce in the collections, which suggests that both known species are specialized and selective in their habitat requirements.

Figures

FIGURES 1 – 3. Chirosiomima spp. 1. C. gestroi, male from Tunisia, habitus. 2. Same, labella. 3. C. obscurinervis, female from Iran, habitus. Scale bars: 1 mm (1, 3); 0.1 mm (2).

FIGURES 4 – 9. Chirosiomima gestroi, male from Tunisia. 4. Sternites IV and V. 5 – 7. Hypopygium in posterior, posterolateral and lateral views. 8. Hypandrium, pregonites, left postgonite and vertical sclerite, anterolateral view. 9. Phallus, lateral view, and ejaculatory pump. Scale bar: 0.25 mm.

FIGURES 10 – 12. Chirosiomima spp. 10. C. obscurinervis, male from Iran, sternites IV and V. 11. C. obscurinervis, lectotype male from Ghana, hypopygium, posterolateral view. 12. C. gestroi, female from Tunisia, oviscapt, flat mount (s = sternite; sp = spiracle; t = tergite). Scale bars: 0.25 mm.

FIGURES 13, 14. Chirosiomima spp., oviscapt, lateral view. 13. C. gestroi, female from Tunisia (s = sternite; sp = spiracle; t = tergite). 14. C. obscurinervis, female from Iran (arrow: hump on sternite VI). Scale bar: 0.25.