McAlpine, David, 2011, Observations on Antennal Morphology in Diptera, with Particular Reference to the Articular Surfaces between Segments 2 and 3 in the Cyclorrhapha, Records of the Australian Museum 63 (2), pp. 113-166: 129-130

publication ID 10.3853/j.0067-1975.63.2011.1585

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The Syrphidae  

The Syrphidae   , whether they form a sister-group to the Pipunculidae   alone or to the whole remainder of the Eumuscomorpha (i.e. Pipunculidae   + Schizophora, see Collins & Wiegmann, 2002) must be considered a key group to understanding much of the basal morphology of the Schizophora. I have taken for initial study representatives of the syrphid genera Melangyna   , Microdon   , Psilota   , Eristalis   , Chalcosyrphus   , Ceriana   . These show slight variation, mainly in proportions of certain parts and degree of symmetry.

Segment 2 ( Fig. 35 View Figures 35, 36 ) is generally of moderate size, with largely concave distal articular surface and completely encircling rim. The rim is usually notched or sinuate on its dorsal margin, but is scarcely so in Microdon   and Ceriana   . Typically, the conus is moderately large, broad, and rather short, with a short ventral chin, and the foramen of articulation is inclined laterally with a tendency to become vertically elongate in some forms. The button is located at the lateral base of the conus where the latter merges with the surrounding articular surface, or is located more dorsally, especially so in Microdon   .

In Ceriana ornata (Saunders)   segment 2 is very different from that of other examined taxa. Both the segment as a whole and the conus are elongate and almost radially symmetrical, the latter distally rounded and clavate. As in the Phoridae   , the clavate condition of the conus renders the separation of segments 2 and 3 for study difficult, even after the connective membrane is snapped by rotation.

Segment 3 in Melangyna   ( Fig. 36 View Figures 35, 36 ) is typical of a number of syrphid genera. The segment is broadly bilaterally compressed, has a broad, relatively shallow basal hollow, and the basal articular foramen is situated on a slight prominence arising within this cavity, but there is no indication of a sub-basal caecum. The arista arises before mid length of the segment on the lateral surface very close to the dorsal margin. Segment 3 of Eristalis copiosa Walker   (and possibly that of related species) differs from the above sacculi occur on the lateral surface and sometimes also on the medial surface. The number can sometimes differ between the right and the left antenna, but often there is just one sacculus, which is located on the lateral surface as in most acalyptrate taxa.

In Ceriana   (already noted for its unusual segment 2) and some related genera (see Vockeroth & Thompson, 1987) the arista is much shortened and located apically on segment 3. Comparison with probable outgroups leads me to believe that the peculiarities of Ceriana   and its allies (tribe Cerioidini   ) are autapomorphies for this group. Thus, the presence of a terminal arista (or style) on a distally tapered segment 3 is an evolutionary reversal, simulating the conditions present in basal eremoneurans.