Afrostoma Skevington, Thompson & Vockeroth, 2014

Thompson, F. Christian & Skevington, Jeffrey H., 2014, Afrotropical flower flies (Diptera: Syrphidae). A new genus and species from Kenya, with a review of the melanostomine group of genera, Zootaxa 3847 (1), pp. 97-114 : 107

Afrostoma Skevington, Thompson & Vockeroth , gen. nov.

( Figs 1A–C , 3A–D )

Type-species. Afrostoma quadripunctatum Skevington & Thompson.

Description. Small, slender black flies. Length: 7–8 mm. Head: Face straight, slightly projecting, with distinct medial tubercle; oral opening about 1.2 times as long as broad; gena narrow; frontal triangle not swollen; antennal sockets confluent; eye bare, holoptic in male, with eye contiguity slightly longer than frontal triangle; antenna short, with basoflagellomere oval; arista long, about as long as antenna, pubescent, with short pile about as long as aristal diameter. Thorax: Black; postpronotum (humerus) bare; notopleuron with indistinct tubercle; scutellum convex, not modified; subscutellar fringe present, of multiple rows; anterior anepisternum bare; katepisternal pile patches broadly separated throughout; metasternum not excavated anteriorly, bare; metathoracic pile patch absent; metapleuron bare; postmetacoxal bridge absent; legs simple; plumula simple, long. Wing: brownish, microtrichose; vein R 4+5 straight; vein M 1 (apical crossvein) oblique, slightly sinuous; alula broad, about as wide as cell cup. Abdomen: elongate, slightly narrower than thorax, segments more or less quadrate, as long as broad, without marginal sulcus. Male genitalia: surstyles symmetric; lingula absent; postgonite free; phallus one-segmented.

Etymology. Afrostoma is an arbitrary word derived from combination of the first letters of Afrotropical and the last letters of Melanostoma . The name is to be treated as neuter as is Melanostoma .

Discussion (including comparative diagnosis). Afrostoma is the sister genus to Melanostoma ( Fig. 2 ) and belongs among the basal syrphine groups in the paraphyletic assemblage known as the tribe Melanostomini or Bacchini (see above). While these flies look like Melanostoma species , close inspection of the metasternum reveals the lack of the basolateral excavation, characteristic of Melanostoma ( Andersson 1970) . Also, the male genitalia lack the specialized synapomorphies of Platycheirus (scythe-shaped gonostylus and basomedial lobe on surstyle).

Afrostoma is very distinctive by its lack of male external secondary characters and biogeography (being endemic to the Afrotropical region where the only other melanostomine group is Melanostoma ).

Figures

FIGURE 1. Afrostoma quadripunctatum Skevington & Thompson, male (specimen USNM ENT 00036401). A. habitus, dorsal view; B. oblique view of head; C. habitus, lateral view. Scale bars: 1 mm.

FIGURE 2. 50% majority rule consensus cladogram of Bacchini species produced from Bayesian analysis of COI data. Clade supports shown are posterior probabilities.

FIGURE 3. Afrostoma quadripunctatum Skevington & Thompson, male genitalia: A. epandrium, lateral view; B. epandrium, dorsal view; C. hypandrium, lateral view; D. aedeagal complex, lateral view. Abbreviations: cerc—cercus; distph—distiphallus; ej apod—ejaculatory apodeme; epand—epandrium; hyp—hypandrium; phalapod—phallapodeme; pgt—postgonite; smp dt—sperm duct; spm sac—sperm sac; sur—surstylus. Scale bar: 0.1 mm.