Cyrtona

Pollock, J. N., 2002, Observations on the biology and anatomy of Curtonotidae (Diptera: Schizophora), Journal of Natural History 36 (14), pp. 1725-1745 : 1727-1732

Cyrtona anatomy

Figure 1 illustrates the general view of the female y. The wings at rest are held one over the other, above the dorsum of the abdomen. The general colouration is cryptic, with patches and bands of dark brown intermingled with lighter brown and nearly white areas. The head has a proclinate fronto-orbital, above that a small reclinate bristle, and above that again a large reclinate bristle. The post-ocellar bristles are cruciate. The antenna has a long–plumose arista. The eyes are bare, and dull olive with bronze re ections in life. The thorax has the strongly convex dorsum characteristic of the family. The disc of the scutellum is bare. Randomly arranged setulae cover the scutum. There is a small dark spot at the base of each dorsal thoracic setula. The subscutellum is well developed. The subcosta is complete. The anal area of the wing is somewhat reduced, and the alula is small. The mid and hind legs bear rows of minute close-set setulae laterally on the tarsi. Under the microscope, particularly with the aid of the SEM, these rows can be seen to be composed of dual, squat, conical setulae. Two of the dual units are drawn in gure 2. Each unit has a socketed component bearing a curved tip, and a slightly shorter, unsocketed bract-like component, closely applied to the side of the rst. The anteroventral face of the front femur bears a short row of bristles (about 6–12) making a distinct ctenidium. The thorax of one specimen was dissected, con rming the presence of the tergal branch to the depressor muscle of the mid-trochanter (TDT muscle).

There are seven pairs of spiracles in the abdomen, symmetrically placed in the membrane. The male postabdomen (gures 3, 4, 5) has well-developed separate tergites 6 and 7: both are symmetrical. Tergite 7 is larger than tergite 6. Sternite 6 is symmetrical; it is quite large in Cyrtona sp. X, but its degree of development diVers in other species. It lacks bristles. In Cyrtona sp. X, a sclerite regarded as sternite 7 is small and strut-like; it is asymmetrically placed on the left latero–ventral aspect of the abdomen, linking sternite 6 and tergite 7. The 10th sternite is represented by a pair of slender struts arranged in the shape of a V. The base of the V is near the base of the cerci, but the two limbs of the V do not quite join each other (gure 4). At the other end, the arms articulate with a pair of appendages termed here presurstyli, corresponding to the parameres in McAlpine’s (1987) treatment of Curtonotum , and lie close to the posterior margin of the hypandrium. The left and right presurstyli, operated by the limbs of the 10th sternite, work as a pair, swinging strongly inwards; this action was observed in living specimens. As shown in gures 4 and 5, the postsurstyli of Curtonotum are absent from Cyrtona , probably due to the absence of the narrowing of the ovipositor segments of the female abdomen in the latter genus, which the appendages are normally adapted to grip externally. The hypandrium bears a pair of small projections regarded as pregonites (gonopods). They lie proximal to the presurstyli (see gure 6); they are not articulated. The cerci are simple and unmodi ed; they are well-separated, blunt, long haired, and inserted laterodorsal to the anus.

Despite certain diVerences between the various species of Cyrtona , in general the aedeagus can be described as symmetrical, bird’s head shaped (i.e. having a swollen base with a long beak-like projection), and usually bearing lateral microspinulated sacs. It is carried on a platform that can be raised or lowered by action of the aedeagal apodeme, which is curved (gure 11), and attached at the other end to the midline of the hypandrium. The aedeagus is also capable of a ‘nodding’ type of articulation on this platform. In some species (e.g. Cyrtona sp. X), there is a small plate present at the posterior base of the aedeagus, referred to here as the cordiform plate, because of its close resemblance to the sclerite of that name in Glossina . Due to the shape of the aedeagus, the gonopore is directed anteriorly with respect to the axis of the aedeagal apodeme, in the resting position (gure 3). The aedeagal apodeme can, however, be protruded, and this carries the aedeagus bodily forward and ventrally so that the gonopore is directed postero–dorsally. The proximal lip of the gonopore is more protruding than the distal lip ( Cyrtona sp. Z, gure 11b). The parameres are perhaps represented by the sclerotized elements arising from either side of the base of the aedeagus, each having its apex fused to that of the opposite partner.

The ejaculatory pump is rather small but robust, detached from the end of the aedeagal apodeme that is attached to the body wall, from which zone the pump is presumably derived, in all Cyrtona species examined. It is possible to trace the ejaculatory duct from the pump almost all the way to the aedeagus (gure 6), by-passing most of the length of the aedeagal apodeme. This proves the identity of the aedeagus on the one hand, and of the aedeagal apodeme on the other.

Each testis ( Cyrtona sp. Y) is a long curved tube having a colourless (or nearly so) wider apical part, with the proximal parts lower down the system having an orange-brown vestiture (gure 7a). A tube from the testis runs parallel to and is bound to its partner, making a double tube, also orange-brown in colour. There are two pairs of male accessory glands, both colourless. One pair (type I) is long, but not quite as long or as wide as the pair of testes: it contains opaque white material. The other pair (type II) is small, appearing as a two-lobed swelling at the junction of these glands and the testes, with the ejaculatory duct: it contains transparent material.

The female abdomen is not adapted for the telescopic extension or withdrawal of the terminal segments as in many ephydroid ies (gure 9a). The rst seven abdominal tergites of the Cyrtona species studied here (females cannot be separated to species until copulating pairs have been obtained) are well formed. There is no abrupt narrowing of the abdomen after segment 5, as there is in Curtonotum quinquevittatum (see below), to make an extensible ovipositor. The 8th tergite is much smaller than the 7th, and it is divided into two lateral parts. The epiproct is simple and complete. The 1st abdominal sternite is vestigial. The 2nd is crescentshaped, the arms embracing the vestigial 1st sternite. Sternites 3–7 are subquadrangulate, forming a series of sclerites of gradually diminishing length, though the width remains constant. The eighth sternite is divided into two lateral symmetrical elements, irregular in shape. There is a very small hypoproct. The cerci are small.

Figures

FIG. 1. Cyrtona sp., left lateral aspect of female y, left wing omitted.