Diopsoidea, Billberg, 1820

McAlpine, David K., 1997, Gobryidae, a new family of acalyptrate flies (Diptera: Diopsoidea), and a discussion of relationships of the diopsoid families., Records of the Australian Museum 49 (2), pp. 167-194 : 168-175

The superfamily Diopsoidea (syn. Nothyboidea)

The Nothybidae and Psilidae

Acz6l (1955) placed the Nothybidae in a separate superfamily, Nothyboidea , from all other Schizophora, because he thought it was the only schizophoran group with the male postabdomen symmetrical and therefore not circumverted. In this he was mistaken, for in many schizophoran families the male postabdomen (particularly in the more or less reduced protandrial segments 6-8) is symmetrical (e.g., Conopidae , Drosophilidae , Ephydridae , Lauxaniidae , Psilidae , Teratomyzidae , etc.). The Dolichopodidae , in which the protandrium possesses groundplan asymmetry, includes also forms with secondary symmetry (D. Bickel, pers. comm.). This is no longer taken as evidence of lack of circumversion of the genital segment, at least historically, in these taxa (see Hennig, 1958; Griffiths, 1972).

Hennig (1958) employed the superfamily Nothyboidea to include the families Diopsidae , Nothybidae , Megamerinidae , Tanypezidae , Strongylophthalmyiidae , and Psilidae , although he was unable to find a single apomorphy to establish monophyly of the superfamily. J. McAlpine (1989) recognised the same superfamily concept as Diopsoidea (on grounds of nomenclatural priority), with the addition of Somatiidae and Syringogastridae . J. McAlpine (1989) considered the Diopsoidea and Nerioidea to be sister groups, but I have found no validity in the evidence presented (D. McAlpine, 1996).

Griffiths (1972) used a revised concept of the Nothyboidea to include only the families Nothybidae , Psilidae , Teratomyzidae , and Periscelididae (the last including Somatia but not Cyamops and Stenomicra ). I do not find the four stated groundplan apomorphies at all convincing as support for his superfamily concept. Among such a diverse lot of taxa, only unusually distinctive apomorphies can provide acceptable evidence for interrelationships, and these four are very widely distributed among acalyptrate families and undoubtedly subject to convergence.

Griffiths also suggested, but simultaneously queried, a sister group relationship between Nothybidae and Teratomyzidae (1972, fig. 16, and accompanying table), supported by the following three apomorphies (from his more extensive listing for nothyboid families): 1, postvertical bristles reduced; 5, axillary lobe and alula reduced; 7, lower basal cell (bm) open anterodistally.

These do not appear to provide a set of primal synapomorphies, because the postvertical bristles, though absent in Nothybidae , are well developed but rather short in the groundplan of Teratomyzidae ; the alula is not as much reduced in the groundplan of Teratomyzidae as it is in many other taxa of elongate acalyptrate flies; the cell bm is not open anterodistally in the Teratomyzidae , but vein 4 has a flexure or weak point in this region. I find such a weakening or flexure in the basal section of vein 4 to be manifested to a variable degree in some taxa of Agromyzidae , Coelopidae , Heleomyzidae , Helosciomyzidae , Pallopteridae , Platystomatidae , Psilidae , Sepsidae , Tephritidae , and Tethinidae . The Teratomyzidae , which have been the subject of a recent study (D. McAlpine & de Keyzer, 1994), are widely different from the Nothybidae in their morphology, except for the simplified, symmetrical protandrium; also the aedeagal characters, which Griffiths considered significant for placement in the Nothyboidea , are quite diverse among the teratomyzids and their groundplan conditions for the family are uncertain. I consider that there is no case for considering the Nothybidae and Teratomyzidae to be closely related.

The Nothybidae and Psilidae show some interesting points of morphological resemblance. There is an enlarged postocular bristle laterad of the outer vertical in Nothybus and in several psilid genera (so that it may be present in the groundplan ofboth families). There are, however, some difficulties in establishing homologies of bristles on the upper part of the head in both families, as indicated by Hennig (1958). There is a general resemblance in antennal structure between Nothybidae and Psilidae , but a more detailed resemblance between Nothybidae and Gobrya , as indicated below. The anterior notopleural bristle is absent in Nothybidae and Psilidae , as in many other elongate flies (see D. McAlpine, 1997). The apparent groundplan for both Nothybidae and Psilidae includes a secondarily symmetrical male abdominal segment 6 with ventrally placed sternite. The groundplan for both families probably includes a largely membranous distiphallus which is ribbonlike and almost symmetrical.

The most likely synapomorphies for Nothybidae and Psilidae would seem to be in the male postabdominal conditions indicated, the subcircular prothoracic spiracle not largely closed over by intermeshed hairs on its outer lips, and the enlarged postocular bristle. As indications of relationship these seem to conflict with the evidence for relationship between Gobrya and Nothybidae reviewed below.

Some of the numerous character states of Nothybidae which differ from those of Psilidae (the latter bracketed) are as follows: (l) distal articular surface of antennal segment 2 facing forwards (facing downwards); (2) lateral arms of ptilinal fissure much abbreviated (moderately long and decurrent on parafacial); (3) prothoracic precoxal bridge extremely broad (absent); (4) subscutellum hypertrophied (not prominent, sometimes vestigial); (5) mesopleural bristle present (absent); (6) pleurotergite setulose, without noticeable pubescence (pubescent, without setulae); (7) tibiae with setulae all aligned in several longitudinal series (tibial setulae irregularly placed); (8) subcosta completely sclerotised distally, terminating in costa close to termination of vein 1 (subcosta desclerotised distally, terminating well before end of vein 1); (9) first and second basal cells partly confluent (completely separated); (l0) alula absent (present); (11) female with spermathecal vesicles (spermathecal vesicles absent,?consistently). In many of these characters the Nothybid state is apomorphic relative to the psilid state, but the psilids are apomorphic in characters 8 (at least partly) and 11. In characters 1, 5, and 6, polarity is uncertain, and, ifNothybidae and Psilidae are not sister-groups, it may not be reasonable to regard a character state present in one family as necessarily directly derived from that of the other.

An intriguing possibility, which I cannot at present regard as a probability, is the following: the Nothybidae are not closely related to any of the families here placed in the Diopsoidea , but are derived from near the Curtonotidae in the superfamily Ephydroidea (syn. Drosophiloidea). Because I cannot completely refute this idea, I point out some evidence for and against it. The Curtonotidae are considered to include the genera Curtonotum , Cyrtona , and Axinota . The following 13 conditions (a-m) could be considered to give some support to this hypothesis.

(a) The antennal structure of Nothybidae , described above, agrees with that of Curtonotum in most details, as it does with most diopsoids (other than Diopsidae ).

(b) In Nothybidae and Curtonotidae the external opening of the prothoracic spiracle is subcircular, instead of having the usual narrowly two-lipped conformation. This feature does not, however, give a separation from Psilidae , as mentioned above.

(c) The scutellum in Nothybidae has two pairs oflarge bristles on its margins. This agrees with Curtonotidae and most other ephydroid taxa, but in the typical diopsoid taxa there is only one large pair of scutellar bristles, the apical pair, and any others are much smaller.

(d) While Nothybidae are noted for the prominently hypertrophied subscutellum, that of Curtonotum more nearly approaches the nothybid condition than any other taxon included in the Diopsoidea .

(e) The presence of a mesopleural bristle in Nothybidae is in disagreement with other taxa here placed in Diopsoidea , but one or two mesopleurals are present in many taxa of Ephydroidea , including the Curtonotidae , but not the Drosophilidae . A mesopleural bristle is so widely present among schizophoran taxa, that its presence does not constitute a very particular point of agreement for the above families.

(f) The setulae on the tibiae in Nothybidae and Curtonotidae are arranged in longitudinal rows, a condition present in many other ephydroids. However, this character does not give a good separation from other taxa of Diopsoidea , many of which show a tendency for these setulae to become seriate.

(g) The tarsi of Curtonotidae (least so in Cyrtona ) are, like those of Nothybidae , remarkably long, slender and subcylindrical. In most other diopsoids the tarsi are either somewhat shorter, in relation to the tibiae, or somewhat more depressed.

(h) The subcosta in Nothybidae , as in Curtonotum , is fully developed to its distal termination in the costa very near but quite separate from the end of vein 1.

The variations in subcostal development in other diopsoid taxa do not include these precise features.

(i) In both the Nothybidae and Curtonotidae the anal region of the wing, immediately beyond the alular region, is narrowed, the margin here showing more or less concave curvature, and the much shortened but sclerotised distal section of vein 6 ends at or near the margin Although basal wing-narrowing occurs in other diopsoid families, it does not follow this pattern. I note here that J. McAlpine (1989) was mistaken in considering vein 7 (A2) to be visible in this region in both Curtonotidae and Cryptochetidae . The correct identities of the anal veins in these flies, as given by Hennig (1958), become apparent when the curtonotid genera are carefully compared with the less reduced forms of Drosophilidae . The structure in Cyrtona illustrates the true position of vein 6 and also shows how a secondary spur is liable to misidentification as vein 6 in the Cryptochetidae . I affirm that there is no trace of vein 7 beyond the alular region in any taxon of either Diopsoidea or Ephydroidea .

(j) In both Nothybidae and Curtonotidae there is a convex longitudinal crease of the wing membrane arising just beyond the origin of the distal section of vein 6. This crease is not the homologue of any true vein, and is not known to me in other taxa of Diopsoidea , though there is a trace of it in a few other ephydroid taxa, e.g., Diastatidae .

(k) In the male postabdomen of Nothybidae and Curtonotidae there is a somewhat similar degree of reduction of sclerites of segments 6 to 8, in contrast to the large tergite and sternite 5, with a tendency towards symmetry.

(1) The male genital segment of Nothybidae and Curtonotidae is directed posteriorly, in contrast to that of most taxa of Diopsoidea and Ephydroidea , in which the genital segment is directed ventrally. In the diopsoid family Psilidae there is also a strong tendency for the genital segment to be directed posteriorly.

(m) Pollock (1996) has recorded ovoviviparity in the curtonotid Cyrtona , a condition which it shares with Nothybus longithorax Rondani. This is apparently an infrequently derived condition in acalyptrate taxa, the few other known cases being listed by Pollock. However, it is not known if it is a groundplan condition for either Nothybidae or Curtonotidae .

Of the above arguments, (a), (b), (f), (k), (1), (m) may be seen as rendering relationships of Nothybidae to Ephydroidea as feasible as to Diopsoidea , while (c), (d), (e), (g), (h), (i), (j) may, to varying degrees, be seen as favouring the hypothesis of ephydroid relationships (with particular reference to the Curtonotidae ) over that of diopsoid relationships.

The above indications of possible relationship between Nothybidae and Curtonotidae seem to be countered by the following points, (n) to (s), which are more in accordance with diopsoid relationships for the Nothybidae .

(n) The Nothybidae lack the postvertical bristle, vibrissa, and seriate postocular setulae, as in Gobrya , Syringogastridae , and Diopsidae . Such a degree of reduction of cephalic bristles is unusual in the Ephydroidea and not found in the Curtonotidae .

(0) The Nothybidae lack the humeral, anterior notopleural, presutural, and sternopleural bristles. This reduction of thoracic bristles is in disagreement with Curtonotidae and most less reduced ephydroids, but is typical of the Diopsoidea .

(P) The Nothybidae lack the preapical dorsal tibial bristle, characteristic of the Curtonotidae , Diastatidae and many drosophilids, but uniformly absent in Diopsoidea .

(q) The costa in Nothybidae lacks the break at the subcostal position. This condition disagrees with probably all macropterous Ephydroidea , but agrees with the diopsoid taxa other than Psilidae .

(r) In the Nothybidae the basal end of the discal cell is strongly enclosed, but the second basal cell is confluent with the first basal cell because of an extensive break in vein 4. This condition contrasts with that in Curtonotidae , where vein 4 is complete but the basal end of the discal cell is confluent with the second basal cell. In those ephydroids with discal and second basal cells visibly separated, the basal crossvein separating them is generally weakly sclerotised. This difference between Nothybidae and typical ephydroids is most readily explained as an independent derivation of each condition from a plesiomorphic condition with both basal cells completely enclosed by well sclerotised veins, as in the Psilidae . A similar pattern of variation in these cells at a lower taxonomic level occurs in the family Neurochaetidae , where the two different apomorphic conditions distinguishing the genera Neurotexis and Neurochaeta have been separately derived from the plesiomorphic condition found in Anthoclusia and Neurocytta (D. McAlpine, 1993) .

(s) the Nothybidae lack the incomplete suture between abdominal tergites 1 and 2, present in the Curtonotidae and other less reduced forms ofEphydroidea. This suture is absent in all typical families of Diopsoidea .

For the above reasons I leave the Nothybidae in the provisional superfamily Diopsoidea . The problem of relationships between Nothybidae and Gobrya will be discussed below.

The Syringogastridae and Diopsidae

The neotropical genus Syringogaster was generally placed in the Megamerinidae until Prado (1969) erected for it the family Syringogastridae in a detailed taxonomic review. Griffiths (1972) regarded the Syringogastridae as the sister group of the Diopsidae (including Centrioncinae ), the two families together forming his "prefamily Diopsoinea". J. McAlpine (1989) accepted family status for Syringogastridae , but placed it as a sister group of Megamerinidae (including Gobrya ), a classification I consider too improbable for further consideration (see D. McAlpine, 1997).

I accept that Syringogastridae and Diopsidae (including Centrioncinae ) are sister groups on the basis of a different set of synapomorphies from those given by Griffiths. I review the eight autapomorphies listed by Griffiths (1972) in support of monophyly of the Diopsoinea as follows, drawing comparisons with other families (numbering as given by Griffiths except that characters (2) and (4) are separated into their components):

(1) Postvertical bristles absent. This is an apomorphy relative to the plesiomorphic state of Psilidae , but, because the apomorphic state is present in the groundplan of outgroups Nothybidae and Gobrya , it cannot be claimed as a primal autapomorphy for Diopsoinea (synapomorphy for Syringogastridae and Diopsidae sensu Hennig, 1965 ).

(2a) Only one fronto-orbital (ors)... present. This is perhaps an apomorphy relative to the presence of two pairs of fronto-orbital bristles, which is perhaps a groundplan plesiomorphy for the Psilidae . The outgroup Nothybidae is subject to interpretation as having one, two, or three fronto-orbitals. Doubt as to whether the foremost frontal bristle of Nothybidae is the homologue of a fronto-orbital (supraorbital) bristle arises from its unusual position, but the doubtfully inferred presence of three fronto-orbitals ( Hennig, 1958: fig. 54) seems not to rest on any firm evidence. Syringogaster has no fronto-orbital bristles, like Gobrya , but there is no evidence as to whether the condition in the former was attained by loss of a single such bristle or by simultaneous reduction of two bristles. For these reasons I am doubtful if the inferred presence of one pair of fronto-orbitals in the groundplan of Diopsoinea is an autapomorphy.

(2b) Only... one vertical bristle (vte) present. This could be a valid autapomorphy, though its interpretation is disputed by Feijen (1989) on improbable grounds.

@ Only one postalar bristle present. As this condition is present in the outgroups Nothybidae , Psilidae , and Gobrya , it cannot be claimed as a primal autapomorphy for Diopsoinea.

(4a) First and second abdominal terga fused, forming syntergum which is the largest sclerite of the abdomen. Partial fusion of tergites 1 and 2 is evidently present in the groundplan of the Schizophora. As complete fusion is present in all likely diopsoid outgroups ( Somatiidae excluded) this cannot be claimed as an autapomorphy for Diopsoinea.

(4b) Basal segments of abdomen (especially the second segment) elongate, but distal segments becoming short and wide, so that the abdomen has a petiolate appearance. This condition is present in the outgroup Gobrya and to a varying extent in many elongate acalyptrate flies of various families. In several primitive diopsid genera the condition is only slightly developed. Hence its status as an autapomorphy for Diopsoinea is unconvincing.

(5) Seventh sternum (male) forming complete ventral band of sclerotisation, fused with inverted eighth sternum on right side... This may be a genuine autapomorphy but it needs more investigation within the Diopsidae where sternite 7 is variable. The fusion of a ventrally placed sternite 7 with sternite 8 on the right side does not occur in outgroups.

(6) Seventh and eighth tergum vestiges (male) lost. This is the condition in all diopsoid families and most other families of Schizophora. It is therefore illogical to give it as an autapomorphy for Diopsoinea.

(7) Seventh left spiracle (male) lying within seventh sternum. While this condition may be in the groundplan of Diopsoinea, its presence in Gobrya , which otherwise has a rather different protandrium ( Fig. 8 ), precludes its recognition as a primal autapomorphy for Diopsoinea.

(8) Aedeagus (male) rather short, with a complex distal section which bears lobes or processes. There is a strong resemblance between the aedeagi ofSyringogaster and certain diopsids (compare figs 79 and 80 of Griffiths, 1972, and the figures of Sphyracephala spp. of Feijen, 1989), even though homology of individual lobes has not been demonstrated. This condition, according to the above general description, occurs also in Gobrya ( Fig. 12 ), but not in the investigated taxa of Nothybidae and Psilidae . The evidence suggests that this condition of the aedeagus may be a synapomorphy for Gobrya and Diopsoinea, rather than an autapomorphy for Diopsoinea.

Despite the above arguments, I believe that the taxa constituting Griffiths' Diopsoinea together form a monophyletic group as indicated by the synapomorphies for Syringogastridae and Diopsidae set out in Table 1. Four of these, (a) the presence of a supra-alar carina, (b) the cylindrical extension of metathorax, (c) the presence of tarsal sawlines, and (d) the reduction of the inner vertical bristles (together with general cephalic chaetotaxy) call for special comment.

(a) The supra-alar carina (Figs 34-36) is a structure which, within my experience, is peculiar to the Syringogastridae and Diopsidae . It is probably at its most primitive condition in Centrioncus (including Teloglabrus , Fig. 35), where it consists of a well-defined ridge on the surface of the mesoscutum passing posterodorsally from the postnotopleural ridge (as defined by D. McAlpine, 1991: 32 -33) to the base of the supra-alar bristle. In the Syringogastridae and most Diopsinae the supra-alar bristle is vestigial or absent (probably as a convergent apomorphy in the two groups), but the carina remains. In the Diopsinae (sensu Hennig), other than the Teleopsis complex (Fig. 36), the supraalar carina is more extended posteriorly than in the Syringogastridae , so that in these forms which possess a supra-alar bristle (or a secondary hair at the summit of the carina) it lies only slightly in advance of the dorsomedially displaced postalar bristle.

In the genus Teleopsis the summit of the supra-alar carina is produced as a large spinous process (the supraalar spine) and the lower part of the carina is more or less obsolete. This highly apomorphic condition is the only modification known to me in the Diopsoinea involving significant reduction of the supra-alar carina. The supra-alar carina is a quite distinct development from the horizontal lamina formed by the postnotopleural ridge in the Megamerinidae , some Coelopidae (genus Coelopa , see D. McAlpine 1991, fig. 7), Curtonotidae (especially Curtonotum ), some Psilidae (genus Loxocera ),

and some Platystomatidae (e.g., genus Giraffomyia ).

(b) The cylindrical posterior extension of the metathorax is found only in the Diopsoinea among the taxa of Diopsoidea and is usually quite short ( Figs 38, 39 ). As a prerequisite to the cylindrical extension, there must be a well sclerotised metathoracic postcoxal bridge to provide support for its lower part. Such a postcoxal bridge is present in all available taxa of Diopsoinea, as in a number of other schizophoran taxa. The upper part of the cylindrical extension is developed from the margin of the metanotum, a sclerite which occurs in most schizophorans as an inconspicuous transversely attenuated rim on the posterior margin of the postscutellum. In the Diopsoinea the metanotum is always somewhat better developed, and in Syringogaster papaveroi Prado it is remarkably large ( Fig. 38 ). A cylindrical extension of the metathorax similar to that of the Diopsoinea occurs in the platystomatid subfamily Angitulinae .

(c) A tarsal sawline consists of a well defined linear longitudinal series of short, compressed cuneate setulae situated on either the anterior or posterior side of a tarsal segment. The sawline is well differentiated from any other longitudinal series of tarsal setulae, its component setulae being typically shorter and more closely placed, so that it may look like a continuous line under low magnification ( Fig. 40 ). Its setulae usually consist of two kinds, which alternate along its length ( Figs 41 -43 ), the larger being longitudinally grooved with the basal socket usually evident, the smaller being almost smooth, arising at a different angle to the larger ones, and without evident basal sockets. However, it should be remembered that the electron micrographs may sometimes fail to show existing basal sockets as they do not indicate more transparent zones of cuticle. Often a larger setula and its distally adjacent smaller setula are set on a common basal prominence as in Fig. 43.

A sawline is present on the mid basitarsus (mid tarsal segment 1) of all diopsids examined except Sphyracephala (Sphyracephala) brevicornis (Say) and even in the latter there is a loose posterior series of less specialised setulae which are probably homologous with the sawline of other genera. In Sphyracephala (Hexechopsis) beccarii (Rondani) the sawline is identifiable on the posterior surfaces of mid tarsal segments 1 and 2, but is somewhat atypical in consisting of longer, less crowded setulae than in most diopsids. Sphyracephala and Pseudodiopsis differ from other diopsids in the absence of sawlines on the hind tarsus, whereas other genera examined have at least the anterior side of hind tarsal segment 1 with a sawline, except Centrioncus , which has well developed sawlines only on the posterior surfaces ofhind tarsal segments 1-4. A sawline is present on the fore tarsus (posterior surface of segment 1 only) only in the advanced diopsine genera (e.g., Diasemopsis , Cyrtodiopsis , Teleopsis , and Diopsis ). In Centrioncus well developed sawlines are present on the posterior surfaces of mid tarsal segments 1-4 and also extend for most of the length of the mid tibia on the posterior surface.

In the two presently available somewhat morphologically divergent species of Syringogaster ( S. papaveroi Prado , Brazil, and Syringogaster sp., Costa Rica, see Fig. 40 ), both anterior and posterior sawlines are present on segments 1-4 of the mid tarsus and anterior ones on the hind tarsus in both sexes, but sawlines are absent from the fore tarsus.

From the distribution of tarsal sawlines in diopsids it can only be confidently stated that the groundplan for the family includes the presence of a posterior sawline on mid tarsal segment 1. There is a possibility, however, that the groundplan includes a more extensive presence of tarsal sawlines, and, in view of their presence in Syringogastridae , Centrioncinae , and Diopsinae , the reduction of sawlines in Sphyracephala is apparently a derived state.

In a non-exhaustive survey of cyclorrhaphous families I have found tarsal structures resembling diopsid sawlines to a varying extent only in the Platypezoidea (syn. Phoroidea; families Ironomyiidae , Sciadoceridae , Phoridae , Platypezidae , but not Lonchopteridae ; Opetiidae not examined), certain Ephydroidea (syn. Drosophiloidea sensu Hennig, 1958), and in the Glossinidae (superfamily Muscoidea = Calyptrata). The survey revealed some diversity in setation and spination of the tarsi. In some groups there are very loose series of spaced spines. In others the setulae of the basitarsus have a tendency to form several longitudinal series, most conspicuous in Neriidae , Nothybidae , and some calyptrates, but, outside the previously mentioned groups, none shows such a distinct, dense, anterior and posterior series as do the Diopsidae and Syringogastridae .

In the Ephydroidea typical basitarsal sawlines occur apparently only in the Curtonotidae and a number of genera of Drosophilidae . In the Drosophilidae they are not restricted, as has been sometimes supposed, to the subfamily Steganinae but occur also in some species of Drosophila ( Castro, 1953, and author's observations). They commonly consist of two kinds of processes alternating in each series, as in the Diopsoinea. The tarsal sex-combs present in males of some Drosophila species are quite different from sawlines. Other ephydroids (e.g., Diastatidae , Camillidae ) have loose longitudinal combs of setulae on the basitarsi, but no sawlines.

The distribution of presence of tarsal sawlines in the Cyclorrhapha suggests that their presence is an apomorphy of infrequent arisal, having probably arisen as few as three times in the Schizophora. Their presence in the groundplans of Diopsidae and Syringogastridae is significant evidence for the monophyly of the Diopsoinea and emphasises its morphological distance from other diopsoid groups.

(d) The genera Diopsina and Cyrtodiopsis include several remarkably hirsute diopsid species (some well illustrated by Feijen, 1981), having many long setulae on the head, legs, scutellum, and other parts of the thorax and abdomen, some of those on the head and thorax tending to a symmetrical arrangement. Also, in Pseudodiopsis there is a linear fringe of setulae on the frontal orbits. In many taxa of Schizophora there are minor setulae on the orbital plates and elsewhere on the head, but these, for the most part, do not intergrade with true fronto-orbital bristles. In those diopsids with setulae or hairs on the ocellar tubercle their size is similar to and dependent on that of the other frontal setulae, and in Cyrtodiopsis they show the same modified apices. However, Feijen (1983) supposes that those setulae which appear to be in the position of ocellar and frontoorbital bristles are in fact the homologues of these bristles in other dipterous families. On this basis he attributes the presence of a pair of ocellar bristles and of "several" fronto-orbital bristles to the groundplan of both the Diopsoinea and the " Diopsidae " (s.str., i.e. the subfamily Diopsinae of Hennig, 1965), and declines to recognise the two really distinct pairs of cephalic bristles present in many diopsines as homologous with the two pairs present in centrioncines. The two pairs of cephalic bristles present in the groundplan of the Diopsidae are most logically treated as outer vertical (vte) and frontoorbital (ors) bristles as indicated by Hennig (1965: figs. 45, 46). Also, it can be stated that, in the groundplan of the Diopsidae , the ocellar bristles are undifferentiated from frontal setulae, though well differentiated proclinate, divergent ocellar bristles are present in the groundplan of Syringogastridae . As the ocellar bristles of Syringogastridae appear to be homologous with those of Psilidae and more remote outgroups, it is probable that their presence is a groundplan plesiomorphy for the Diopsoinea.

In addition to the autapomorphies for the Diopsoinea given in Table 1, the presence of densely microtrichose crazed cuticle on the face is almost certainly a groundplan condition for Diopsoinea, and may be an autapomorphy. It is present, with some variation, in Centrioncus , Sphyracephala , and Syringogaster (Figs 20, 22, 24), i.e. in all major clades of Diopsoinea, or at least in their more "basal" taxa ( Sphyracephala being a remarkably primitive genus of Diopsinae ). The crazed appearance of this cuticle is produced by numerous fine but apparently deep suture-like grooves, with a mainly almost vertical orientation. Some of the grooves appear to widen in an irregular manner, probably through shrinkage of the cuticlr in drying. The grooves divide the surface of the cuticle into many vertically elongate plates, most of which bear a single microtrichium each. The scale-like structures on the face of Syringogaster are homologised with microtrichia, or at least with their dilated bases, because of their similarity to the facial microtrichia of Centrioncus (compare Figs 20, 22).

Because of lack of knowledge of ultrastructure of the face in other acalyptrate families, I hesitate to class the presence of densely microtrichose crazed cuticle on the face as a definite autapomorphy of the Diopsoinea, though it may be so.

The parafacial of Centrioncus , Sphyracephala , and Syringogaster has a dense covering of "pubescence", in the first two of similar size to that on the face. However, these parafacial hair-elements differ from those on the face in being wholly or partly socket-based macrotrichia (Fig. 23). (Electron microscopy does not always enable

ready discrimination of macrotrichia from microtrichia as the membranous rings surrounding the bases of the former are distinguishable only if somewhat sunken). I therefore regard the presence of dense, minute parafacial macrotrichia as a groundplan condition of Diopsoinea, but I cannot determine if it is an autapomorphy for Diopsoinea, because it has not yet been demonstrated if the condition is also present in outgroups.

The absence of any dorsocentral bristle is a groundplan apomorphy for the Diopsoinea, judging from the universal absence of such a bristle among the included taxa. I do not, however, treat the condition as an autapomorphy, as it is shared with the outgroup Gobrya . Presence of a dorsocentral has been claimed for some diopsids, but this is an error. The large bristle that looks like a dorsocentral in some taxa (e.g., in fig. 61.1 of Peterson, 1987) is the medially displaced postalar bristle, as discussed below. The pitting along the median ventral suture of the sternopleura in some taxa of Diopsoinea shows some interesting diversity. In Syringogaster sp. ( Fig. 26 ), there is a single median series of relatively few, spaced, deep pits, of which the foremost is the largest The suture is apparent as a dark internal line (therefore not visible in the electron micrograph). The condition in Centrioncus spp. is very similar, but the pits are more numerous and crowded. In most Diopsinae the median sternopleural suture is externally apparent as a groove or ridge, sometimes as a narrow ridge lying within a groove. In most diopsine taxa there are no pits associated with this suture, but in Sphyracephala sp. ( Fig. 27 ), a somewhat primitive diopsine, there is a series of pits on each side of a slight median ridge.

A possible evolutionary sequence for these structures is as follows. The uniform median groove, representing the median ventral suture in such outgroups as the Psilidae , has become sunken in such a way that it is represented on the surface only by a series of pits (as in Syringogaster and Centrioncus ). A further strengthening of the suture brought about emergence of the suture as a surface ridge dividing the originally uniseriate pits in two (as in Sphyracephala ) Further modification of the thorax brought about loss of the pits (as in Cyrtodiopsis , Diopsis etc). In Gobrya cyanea there is weak transverse rugosity on the posteroventral parts of the sternopleura ( Fig. 25 ), but this condition cannot form part of the above series, as Gobrya lies outside the Diopsoinea phylogenetically.

Because the above sequence is inferred partly from a particular interpretation of phylogeny within the Diopsoinea, it cannot be classed as primal evidence for inferring phylogenetic relationships among the included taxa. It is reasonably certain from their taxonomic distribution that median sternopleural pits occur in some form in the groundplan of the Diopsoinea. Because what appear to be rudimentary sternopleural pits occur in Gobrya , I do not list the presence of these pits as an autapomorphy of Diopsoinea.

The assertions of Feijen (1983; 1989), that the (probably upper Eocene) fossil Prosphyracephala was

a true sphyracephaline contemporary with true diopsines, and that Syringogastridae and Centrioncinae (Centrioncidae in Feijen's classification) are sister groups which separated from each other before the end of the Cretaceous, do not arise from a logical treatment of the available data. In my view, the primary groupings of Diopsidae given by Hennig (1965) are more likely to be phylogenetically valid than either those of Feijen or those of Steyskal (1972).

The family Syringogastridae was well characterised by Prado (1969) and treated as a monophyletic group by Griffiths (1972). J. McAlpine (1989: table 116.2) gave several autapomorphies for the Syringogastridae , but unfortunately treated the remotely related Megamerinidae as the relevant outgroup. Therefore the majority of given character states, though apomorphic in the broader field, are not autapomorphies for Syringogastridae . The following four conditions (a-d) would appear to be distinctive syringogastrid autapomorphies, if they can be confirmed for more species than are at present available to me.

(a) Pleurotergite, without convex callus. In outgroups of various levels in the Schizophora there is a convex callus on the pleurotergite, which, in the Diopsinae , bears a cuticular spine, unfortunately termed "metapleural spine" by Feijen (1983).

(b) Anterior margin of metathoracic spiracle with blunt cuticular spine (Fig, 29). This is a distinctive syringogastrid condition, not encountered in outgroups.

(c) Median panel offace with dense covering of scales (Figs 19, 20). These are probably modified microtrichia (pruinescence) as suggested by comparison with the corresponding surface in Centrioncus (Fig. 22), but I have not encountered a similar facial vestiture in my limited studies of other flies under the scanning electron microscope.

(d) Subscutellum vestigial ( Fig. 31 ). In most taxa of Diopsoidea there is a distinguishable subscutellum between the scutellum and postscutellum, which forms a convexity separate from that of the latter. A convex subscutellum of variable size is present in the Diopsidae and in Gobrya ( Fig. 30 ), but in the available syringogastrids it can be detected only as a linear rim on the dorsal margin of the postscutellum bordering the subscutellar membrane.

As the family Syringogastridae includes a single genus, Syringogaster , of limited morphological diversity ( Prado, 1969), its monophyletic status seems very probable, though I cannot yet prove that all the above conditions are in its groundplan.

The family Diopsidae has been characterised as a monophyletic group by Hennig (1958) and Griffiths (1972). Because some of the character states given as evidence for monophyly, particularly in the list of Hennig, are not demonstrably groundplan autapomorphies for Diopsidae , I would base my argument for monophyly principally on the following six autapomorphies (a-f).

(a) Antenna porrect; segment 2 not cap-like, without dorsal slit or seam; segment 3 short, not dejlexed, without dorsobasal process fitting into cavity of segment 2, with aristal insertion not closer to basal than to distal extremity (see Feijen, 1983: figs 4-6). The antenna of Syringogastridae ( Figs 17, 18 ) has much the same complex structure as that of the Psilidae as described below among groundplan characters ofDiopsoidea. Also, the arista is bipectinate. These features, with the possible exception of the bipectinate condition of the arista, which is variable in the Psilidae though a consistent condition ofNothybidae and Gobrya , are p1esiomorphic compared with the contrasting features of the Diopsidae , in which the antenna has more simplified articulation between segments 2 and 3, and more nearly dorsoventrally symmetrical segment 3.

Feijen has reversed the evolutionary polarity of most of these antenna1 features in the Diopsoinea so far as he has described them, but it must be pointed out that the condition in the most acceptable outgroups to the Diopsoinea is similar to that of Syringogastridae . The strongly dorsoventrally asymmetrical segment 3 with arista inserted dorsally well before mid-length, is very probably a groundplan condition of the Schizophora (and perhaps a synapomorphy for Syrphoidea and Schizophora, Cumming et al. 1995). The condition present (to variable degrees) in typical representatives of the Pseudopomyzidae , Neriidae , C1usiidae, and Diopsinae is almost certainly apomorphic.

(b) Postalar bristle displaced dorsomedially (Fig. 35). The Syringogastridae retain the probably plesiomorphic position of the postalar bristle on the lateral surface of the mesoscutum, no higher than the summit of the supraalar carina (Fig. 34), as in the outgroups Psilidae , Nothybidae , and Gobrya . In the Diopsidae the postalar bristle has moved to a more dorsomedial position and in some taxa has subsequently lost its distinction from the mesoscutal setulae (as in Fig. 36). The degree of displacement of the postalar in Centrioncus , though quite noticeable, is less extreme than in other diopsids (subfamily Diopsinae ).

(c) Sockets of major pair of scutellar bristles situated at apices of elongate horn-like processes. This condition is present in all taxa of Diopsidae , but is absent in all out-groups (e.g., Syringogastridae , Gobrya , Figs 30, 31 ). Setiferous scutellar horns have arisen independently in several families of Schizophora (e.g., Chloropidae , Ephydridae ), but only in the platystomatid subfamily (? or tribe) Angitulinae do they closely resemble those of Diopsidae . This is interesting, because the Angitu1inae are also convergent with Diopsoinea in metathoracic structure and the nature of the articulation between thorax and abdomen.

(d) Fore coxa andfemur enlarged (fore leg raptorial). This condition in the Diopsidae is accompanied by the presence of short, incrassate, seriate ventral fore femoral bristles of variable distribution. Such bristles are present in outgroups of two different degrees of removal, viz. Syringogastridae and Gobrya , but these groups, as well as all other families of Diopsoidea , lack the enlargement and raptorial modification of the foreleg: hence the deduction that lack of the raptorial modification is the plesiomorphic state for Diopsoinea. Somewhat similar raptorial enlargement of the foreleg to that of Diopsidae has evolved infrequently in other schizophoran taxa, e.g., in Ochthera and Stratiothyrea (Ephydridae) , Aragara (Chloropidae) , Rhinotora and allied genera ( Heleomyzidae ), and to a less marked extent in certain sepsids and other taxa.

(e) Basal crossvein (tb, bm-cu, or base of M3+4) absent. Among families referred to the Diopsoidea this condition is present only in the Diopsidae . The condition has arisen several times in the Schizophora, mainly in taxa of small body size. Its occurrence is rarer in groups with the size range ofDiopsidae, e.g., certain curtonotids, which have probably undergone an increase in size, as evidenced by the smaller body-size in their outgroups.

It is not an aim of this paper to elucidate in detail the internal phylogeny of the Diopsidae , but I note that the characters which are used by Steyskal (1972) and Fe~jen (1989) to characterise the Sphyracephalini or Sphyracephalinae include no likely apomorphies. Pseudodiopsis therefore remains a possibly distinct genus from Sphyracephala in my view, as in that of Hennig (1965) and others, because I can find no demonstrable synapomorphies uniting it with Sphyracephala . Also, the phylogenetic diagram of Shillito (1971) is not based on principles of Hennigian cladistics.

Feijen (1983) has demonstrated that Centrioncus is a polytypic genus, though previously entomologists determined all specimens from many African countries as C. prodiopsis Speiser (e.g., Steyskal, 1970a). Feijen has further grouped these prodiopsis-like species into two genera, Centrioncus s.str. and Teloglabrus , though the slight differences given in his key, some of them admittedly inconsistent, would hardly seem to justifY generic segregation. However, he states that: " Centrioncus [s.str.] are characterized as a monophyletic group by the followinggroundplanconditions, whichareapomorphous with respect to the groundplan of the Centrioncidae: (1) Costal cell partly or wholly glabrous. (2) Subcostal cell absent." These character states are also given in his table 4. I have checked these characters for my available specimens of Centrioncus (s.str.) decoronotus Feijen and three " Teloglabrus " spp. (from South Africa and Zimbabwe, not readily identifiable from Feijen's key). Among the numerous specimens of C. decoronotus there is a little variation in the microtrichiation of the costal cells, but the range of variation among the " Teloglabrus " spp. is extreme, as indicated in Feijen's own key. These centrioncine flies have a much reduced subcostal cell because of the close proximity of the subcosta to vein lover most of its length, and separation of the two veins is best appreciated in anterodorsal aspect. The subcosta touches or almost touches vein 1 on part of the extent of the second costal cell, but has distinct and complete sclerotisation, and, though there is a distal divergence at the pterostigma, the intervening space is partly sclerotised. I am unable to demonstrate a significant degree of difference in my material of the centrioncine taxa in the separation of these two veins. Feijen's study is based on a much larger range of centrioncine taxa than is my present one, but, even with this reservation, it is apparent that neither of his two stated apomorphies can be logically treated as evidence for accepting a monophyletic group Centrioncus sensu Feijen. I therefore recommend that Teloglabrus Feijen be treated as a synonym of Centrioncus Speiser.

Shillito (1971) and Feijen (1989) refer to a median suture-like groove of the facial region of some diopsids as the facial sulcus. A comparison between various diopsid taxa, commencing with the less apomorphic Centrioncus , shows that the facial sulcus does not divide the face medially as has beenassumed, butthatthe facial sulcus is actually the face, which has become greatly narrowed in more advanced diopsids (e.g., Diopsis , Teleopsis ) by the encroachment of the more strongly sclerotised parafacial. The supposed absence of the sulcus in species of Sphyracephala and Pseudodiopsis ( Feijen, 1989: p. 68) is due to smaller difference in degree of sclerotisation between parafacial and face and less narrowing of the face in these taxa (see Fig. 23). Differences in degree of development of the facial sulcus among the groups within the genus Sphyracephala may have been exaggerated. Among the diverse Sphyracephala material available to me, the specimen with the seemingly most distinct facial sulcus is one of S. brevicornis (Say) in which the face has collapsed slightly in drying. The distinction between face and parafacial in Sphyracephala is demonstrated by the presence of microtrichia on the crazed cuticle of the former (Fig. 24), compared with minute socket-based macrotrichia on the smooth cuticle of the latter (Fig. 23), though this is hard to appreciate without electron microscopy.

The so-called facial teeth of certain diopsids are lobes on the ventral margin of the genoparafacial sclerite, not of the face.

Figures

Figs 5-12. 5, Nothybus decorus, left antenna, vestiture and arista (segment 6) simplified. 6, Gobrya cyanea, antennal segments 3-6 (note absence of segments 4, 5). 7, Somatia aestiva (Fabricius), antennal segments 3-6. 8, G. cyanea, protandrogram (sclerites of segments 5-8 of male abdomen shown as if split along median ventral line and spread flat). 9, G. cyanea, female postabdomen, ventral view. 10, 11, G. cyanea, epandrium and associated structures, posterior and right lateral views. 12, G. cyanea, aedeagus, right lateral view. c, cercus. ds, compound dorsal sclerite probably including tergite 6 and stemites 6 to 8. ep, epiproct. s5 -s7, stemites 5-7. ss, surstyli. t5-t8, tergites 5 to 8. ts6, tergostemite 6.

Figs 38-43. 38, Syringogaster papaveroi, metathoracic region, right lateral view x75, abdomen and haltere removed, secondarily enlarged metanotum indicated. 39, Cyrtodiopsis sp., metathoracic region and base of abdomen x79, abdominal tergite 1 (indicated) concealing metanotum. 40, Syringogaster sp. (Costa Rica), mid tarsus, anterior view x22l, sawline indicated. 41, the same, detail of sawline on mid basitarsus x2250. 42, Centrioncus decoronotus, part of posterior sawline of mid basitarsus x1740. 43, Cyrtodiopsis sp., the same x1485.

Figs 25-31. 25, Gobrya cyanea, median ventral region of stemopleura x358, showing rugosity (7 incipient stemopleural pits). 26, Syringogaster sp. (Costa Rica), median ventral region of stemopleura x185, showing single median series of pits. 27, Sphyracephala beccarii, median ventral region of stemopleura x235, showing double series of pits. 28, G. cyanea, part of left side of thorax x165, showing metathoracic spiracle, katepimeral membrane indicated. 29, Syringogaster papaveroi, same part of thorax x162, haltere removed, cuticular spine indicated. 30, G. cyanea, scutellum and postscutellar structures x149, subscutellum indicated. 31, Syringogaster sp. (Costa Rica), same parts x127, subscutellum obsolete.

Figs 13-18. 13, Gobrya cyanea, head, facial view xSO. 14, G. cyanea, vertical region of head xl0S. IS, G. cyanea, region of antennal bases x249, ptilinal fissure indicated. 16, G. cyanea, base of arista x800, showing direct insertion of segment 6 into socket of segment 3. 17, Syringogaster sp. (Costa Rica), facial region of head and antennae x144. 18, the same base of left arista x1990, segments 4, S indicated.