Platypezidae

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 : 125-126

The Platypezidae and Opetiidae

I treat these two families together primarily because of similarity in antennal structure. The molecular study by Moulton & Wiegmann (2004) indicates that they probably together form a clade. See also Chandler (1998) and Collins & Wiegmann (2002a).

Segment 2 in platypezids is generally of primitive form for the Cyclorrhapha, but is variable in some significant characters. I believe that true platypezids, in common with Opetiidae , lack a conus, and that the attribution of a conus to Plesioclythia (now included in Lindneromyia ) by Disney (1988: fig. 5) is due to a slightly prominent annular ridge only. Sometimes the distal articular surface is flattened (as in Melanderomyia and Lindneromyia sensu Chandler, 1994 ; see D. McAlpine, 2008: figs 5, 8) but the rim is either indistinct or only slightly angular. The annular ridge in these genera (also in Agathomyia and Microsania ) defines an area of variable size near the centre of the articular surface, and is well marked by its prominent, coarse, incurved microtrichia. In Opetia the annular ridge is particularly incrassate, but the rim is quite absent ( Fig. 1 ). In Lindneromyia the rest of the articular surface is covered with many short, inwardly inclined, tile-like ridges, each bearing a row of microtrichia. The button in the Platypezidae and Opetiidae is located on the dorsolateral part of the distal articular surface, as in most flies of orthorrhaphous grade.

Segment 3 of the Platypezidae and Opetiidae much resembles that of more plesiomorphic taxa of Orthogenya in that it usually tapers distally to the terminal arista and is probably always without true sacculi such as those present in most taxa of Eumuscomorpha. The smoke flies, Microsania , are perhaps unique among the platypezids in possessing two deep pit-like hollows, one dorsomedial and one ventral, on segment 3, the postpedicellar pouches (see Fig. 28 ). However, this condition is almost identical to that of the orthogenyan genus Hormopeza , which is also attracted to smoke by odour ( Kessel, 1960; Sinclair & Cumming, 2006). The latter authors refer to these hollows as “sensory pits” in their text (2006: 73) and as “pit glands” on their figs 8 and 47. The taxonomic distribution of the pedicellar pouches renders it improbable that they are homologous structures in Hormopeza and Microsania , or that they can be homologous with the sensory sacculi in typical taxa of Eumuscomorpha. Also, the pouches in Microsania and Hormopeza do not contain trichoid sensilla, which characterize the sacculi of those eumuscomorphans in which they have been investigated. More detailed examination of ultramicroscopic structure is beyond the scope of the present work. In Opetia and some platypezids (e.g., Microsania , Fig. 28 ) segment 3 bears one or more relatively large socket-based bristles or macrotrichia. This is an unusual condition in the Eremoneura.

The arista of typical platypezids is three-segmented, but that of Opetia has fewer segments ( Fig. 27 ), as recorded by Hennig (1976), Chandler (1998), and Sinclair & Cumming (2006). In view of the many independent examples of secondary reduction in aristal segmentation in Cyclorrhapha (D. McAlpine, 2002), I have suggested that the condition in Opetia may not be plesiomorphic or indicative of wide phylogenetic isolation of the taxon. The Cretaceous Electrosania cretica Grimaldi & Cumming, 1999 , is also a platypezid-like fly with a two-segmented arista.

While the partial to complete fusion of abdominal tergites 1 and 2 is usual among the Cyclorrhapha (generally quite free in Orthogenya, but also in Phoridae s.l.), Opetia nigra Meigen shows sexual dimorphism in this character. The male has tergites 1 and 2 fused so as to leave no intervening intersegmental membrane, but a line of demarcation is generally visible, taking the form of a slight groove in available specimens. This condition is essentially similar to that of both sexes of typical platypezids (e.g., Lindneromyia spp. ). The female of O. nigra has tergites 1 and 2 completely separated by intersegmental membrane so that the posterior margin of tergite 1 is free to overlap broadly the anterior margin of tergite 2, and tergite 1 is shorter than in the male of the species. I have examined dried specimens and others cleared in lactic acid of both sexes of O. nigra for this character. The condition for the female can also be inferred from the illustration by Chandler (1998: fig. 2.12).

Cyclorrhaphans with a conus

The remaining families of Brachycera-Cyclorrhapha either have a distinct conus on segment 2 (see Hennig, 1976: 54–56) or are derived from forms possessing a conus with subsequent reduction (e.g., Periscelis , Fig. 100 ). Almost all these taxa also have an angular or flange-like, more or less encircling pedicellar rim.

The lower cyclorrhaphous families Lonchopteridae , Opetiidae , and Platypezidae are misplaced in the otherwise informative cladogram for the Eremoneura by Grimaldi & Engel (2005: fig. 12.78), through errors regarding the development of the conus (op. cit.: table 12.7, character 19).

Figures

Figures 1, 2. Segments 1 and 2 (scape and pedicel) of left antenna, after removal of seg. 3, lateral view, of

Figures 26–28. Antennal structure in some basal cyclorrhaphans. (26) Opetia nigra Meigen, male (fam. Opetiidae), left antennal seg. 2 after removal of seg. 3, distal view. (27) The same, left seg. 3 and arista, lateral view. (28) Microsania arthuri Chandler (fam. Platypezidae), left seg. 3 and arista, medial view. pp, postpedicellar pouches.

Figures 99–104. Antennae of Periscelididae. (99) Periscelis fasciata Mathis, right seg. 2, distal view, seg. 3 removed. (100) The same, annular ridge and associated parts. (101) Planinasus sp. (Brazil), annular ridge and associated parts of left antenna. (102) Planinasus sp. left seg. 3, medial view. (103) Stenomicra “sp. B” (Upper Allyn, N.S.W.), the same view. (104) Cyamops sp. (Tuglo, N.S.W.), the same. bf, basal foramen of seg. 3; bs, basal stem; bu, pedicellar button; ca, caestus; d, disc of seg. 3; fc, foraminal cusp; st, scabrous tongue.