Psilidae

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 : 149

The Psilidae and Syringogastridae

These families have been placed in the superfamily Diopsoidea by D. McAlpine (1997). Examples of Psilidae used for detailed antennal study include Chyliza sp. (from Imbia, Papua New Guinea, Figs 112, 113, 115 ) and Psila fimetaria (Linné) (from Switzerland). Specimens of Syringogaster spp. (from Costa Rica, Figs 114, 116 , and Brazil) were used.

The Psilidae have often been characterized as having segment 2 with a dorsal cleft, slit, or seam, i.e. the rim is strongly produced to form a pair of broad, narrowly separated cucullate dorsal lobes, as in numerous other schizophoran families (see D. McAlpine, 1997). This structure produces a cap-like appearance with the hollowed distal articular surface facing distoventrally or ventrally. Much of the concave distal surface is covered with a reticulation of raised ridges and is microtrichose to a variable degree. The conus is virtually absent. The annular ridge forms an almost symmetrical convexity sunk within a deep median cavity of the upper part of the articular surface, sheltered or almost concealed by the lobes of the rim, and bearing numerous stout, incurved microtrichia. The button is located dorsolaterally, just outside this circlet of microtrichia in Chyliza sp. It could not be found in Psila fimetaria , apparently because of the extremely irregular and deeply recessed cuticular surface. The foraminal ring is vertically elongate, with a variably developed dorsal and ventral cusp. A caestus, consisting of a series of prominent, almost separate tubercles is present on each side of the foraminal ring.

These features coincide to a quite remarkable degree with those described for the Neurochaetidae and some taxa of Periscelididae . Though this may suggest at first glance a close relationship between these families, I can find no particular shared non-antennal characters to support such a relationship, and many of the antennal features also occur in other families.

In Syringogaster sp. (family Syringogastridae ) both segments 2 and 3 are very similar to those of the Psilidae in essential structure. The distal articular surface of segment 2 ( Fig. 114 ) is deeply concave because of the pair of large incompletely separated lobes formed from the rim; there is no elevated conus; the approximately symmetrical annular ridge is sunk into the cup; the foraminal ring has a dorsal and a ventral cusp; there appears to be a ridge close inside the annular ridge on each side representing a caestus (difficult to see because this region is deeply recessed). Segment 3 ( Fig. 116 ) resembles that of the Psilidae particularly in the long basal stem bearing the ventrally directed symmetrical foramen on a ventral prominence.

The Syringogastridae have been regarded as the sister group of the Diopsidae s.l. ( Griffiths, 1972; D. McAlpine, 1997), despite their greater resemblance to the Psilidae in antennal structure. The view of Feijen (1983) that the Syringogastridae form the sister group of the “Centrioncidae” (as distinct from the Diopsidae s.str.) was rejected by D. McAlpine (1997), and the present study seems to provide further evidence against Feijen’s viewpoint. However, I am not at present inclined to abandon the theory of close relationship between Syringogastridae and Diopsidae s.l. solely on antennal characters. Of the six distinctive apomorphies shared by Syringogastridae and Diopsidae (D. McAlpine, 1997: table 1) none is present in the Psilidae . In addition, the small, transverse basal articular foramen of the syringogastrid fore coxa is like that of typical diopsids, in contrast to the longer, oblique foramen of the Gobryidae and Psilidae ; and the complex, crazed cuticle of the central part of the face in Syringogastridae somewhat resembles that of various diopsid genera (see figs 20, 22, 24 in D. McAlpine, 1997), while the Psilidae have the face with continuous, unbroken sclerotization.

Figures

Figures 112–118. (112) Chyliza sp. (Imbia, P.N.G.; fam. Psilidae), left antennal seg. 2, distal view, seg. 3 removed. (113) The same, annular ridge and associated parts within pedicellar cup. (114) Syringogaster sp. (Costa Rica; fam. Syringogastridae), left antennal seg. 2, distal view. (115) Chyliza sp., left antennal seg. 3, medial view. (116) Syringogaster sp. left antennal seg. 3, lateral view. (117) Nothybus decorus de Meijere (fam. Nothybidae), left antennal seg. 3, medial view. (118) Gobrya cyanea (Enderlein) (fam. Gobryidae), the same. a6, antennal seg. 6; as, abraded surface; bf, basal foramen; bs, basal stem; ca, caestus; cu, pedicellar cup; pc, pedicellar cleft; r, dorsal lobes of rim; sbc, sub-basal caecum; sc, sacculus; st, scabrous tongue.