Metapone madagascarica, Gregg, R. E., 1958

Gregg, R. E., 1958, Two new species of Metapone from Madagascar (Hymenoptera: Formicidae)., Proceedings of the Entomological Society of Washington 60, pp. 111-121 : 111-115

Metapone madagascarica sp. nov.

Worker. - Length, 6.91 mm.; head length (excluding mandibles), 1.50 mm.; head width, 1.08 mm.; head index, 0.72; thorax length, 1.83 mm.

Head, even without the mandibles, distinctly longer than broad (about 1 and 1/3 times longer than broad), widest in the occipital region and tapering concavely to the mandibular insertions where it is narrowest; occipital margin broadly and shallowly excavated, and concave. Head decidedly convex antero-posteriorly as well as transversely; gula convex; median cephalic groove very weakly indicated, becoming obsolete on the clypeus where it is replaced by a low, rounded carina, posterad. Frontal area absent, its position taken by a broad, curved epistomal suture which delimits the posterior border of the clypeus, and extends between the widely separated frontal carinae. The carinae are straight, parallel, and prominent where they cross the clypeus as trenchant ridges to its anterior margin, abruptly divergent and almost transverse at the antennal insertions, and again turning sharply backward through right angles, and continuing posteriorly to the region of the vertex, flaring slightly. The surfaces of the head below the carinae are broadly concave, forming shallow but distinct antennal scrobes, bounded and overhung by the carinae, though open ventrally. Median lobe of clypeus nearly quadrate, weakly and concavely truncate anterior to its small carina, and bidentate, that is, armed with two, small, blunt teeth projecting forward, and separated by a distance equal to the base of either. Lateral clypeal lobes narrow, sinuate, convex, and separated, from the genae by faint lines continous with the median portion of the epistomal suture. Ocelli absent; no ocellar pits. Compound eyes reduced to mere vestiges composed of 6 to 8 very minute and indistinct ommatidia; located on the sides of the head, at a point barely past the center as measured from the mandibles to the occiput, and on the edge of the scrobe. Mandibles stout, convex, anterior margins feebly carved to nearly straight, the masticatory border bearing five, heavy, blunt teeth, the apical ones best developed and the others diminishing slightly in size. Antennae 11-segmented; scapes short, flat, about 2 1/2 times as long as wide, with convex anterior and straight posterior margins; scapes almost fill the upper and deeper portions of the cephalic scrobes where they are overarched by the facial carinae. Funiculi longer than the scapes, decidedly flattened, but with the upper surface weakly convex and the lower surface flat to almost imperceptibly concave; funicular segments 2 to 7 much broader than long and gradually increasing in size; last three segments much larger, forming a spatulate club, the penultimate and antepenultimate members of which are nearly as broad as long, the terminal segment longer than broad and twice the length of the penultimate.

Thorax long and narrow, about 2 1/2 times as long as broad, and narrower than the head; humeri well-developed, Pro- and mesonotum fused with no trace of dorsal sutures; meso-epinotal suture distinct and slightly impressed, especially laterad. Entire thorax including epinotum, marginate to submarginate laterally, the bordering ridge continuing transversely across the front of the pronotum, setting off a distinct collar which joins the head at a low level. The margins continue also to the epinotal angles which then terminate in broad, dentate processes at the same level as the thorax, and finally turn ventrally to border the declivious face of the epinotum. Dorsum of the thorax moderately convex from side to side, feebly from anterior to posterior ends; basal face of epinotum nearly horizontal, but passing through an abrupt, slightly concave angle to the vertical declivity; basal face twice as long as the declivious face. Thoracic pleurae and epinotal sides vertical but noticeably concave. Petiole almost flat dorsally, subquadrate except that the posterolateral corners are divergent and produced into prominent teeth; the posterior border is broadly excised. The dorsum is separated from the sides, front, and back walls by marginate borders, the walls concave in each case, descending and converging mesially toward the midline, thus producing the appearance of a flaring, cuneate, petiolar node. Anterior peduncle short and constricted; posterior peduncle hardly more than an acetabulum for the condyle of the postpetiole. Petiole armed with a thin, translucent, median, ventral, blade-like keel, pointed at its middle. Postpetiole 2/5 wider than long, almost flat dorsally, marginate on all borders, but the ridge more rounded than the corresponding one on the petiole; anterior and lateral walls vertical and not tapering mesially, the post-petiolar node being thus no broader than the body of the segment. Anterior peduncle short, posterior- peduncle obsolete, the postpetiole joined to the gaster by a wide face, though leaving a deep constriction between the two. Ventral surface of postpetiole produced into a short, triangular, transverse tooth, as a ventral extension of the anterior wall. Mesothoracic spiracles appear to be covered by backward extending flaps developed from the tops of the pro-mesothoracic pleural sutures. Epinotal spiracles large and easily visible. Petiolar spiracles located at the base of the anterior peduncle, postpetiolar spiracles laterally on the node of this segment. Spiracles present on the first three gastric segments.

Gaster elongate, about as long as the combined lengths of the thorax, petiole and postpetiole, or a little shorter; elliptical, rounded and convex in all directions, the anterior border blunt while the posterior end terminates in a somewhat pointed pygidium that is faintly concave on its dorsal aspect, but deflected ventrad. Abdomen furnished with a small sting, partly concealed.

Coxae stout and bulbous. Femora inflated, especially of the meso- and metathoracic legs (about 1 1/3 times as long as broad), and laterally compressed, their ventral surfaces longitudinally grooved for the reception of the tibiae. Tibiae stout and partly compressed but less so than the femora. Foretibia armed with one small spine and a large, pectinate spur; the lower side of the fore-basitarsus pectinate for its full length, its apex ending in three stout teeth. Mesotibia provided with a small, barely pectinate spur, and three, stout apical teeth, two of them approximated; meso-basitarsus armed with three terminal teeth. Metatibia and meta-basitarsus idential with those of the middle leg, though more strongly developed. All tarsi equipped with large claws.

Sculpture - Clypeus, frons, genae, and antennal scrobes covered with fine, longitudinal striae, essentially parallel, but which fade out posteriorly, leaving the vertex, occiput, and posterior part of the genae, smooth and very shining, interrupted only by piligerous punctures. Anterior third of the gula similarly striate, posterior portion smooth and shining. Mandibles longitudinally striate and punctate. Entire dorsum and pleurae of thorax, including the epinotum, longitudinally striate (somewhat oblique on the pleurae), but the striations slightly finer than that of the cephalic sculpture, and diverging to the epinotal corners. Top of the petiole showing well-separated, hair-bearing punctures, its sides striate. Postpetiole and gaster with similar but finer punctures, and a faintly coriaceous texture. All areas of the body, even where most heavily striated, bright and shining due to absence of inter-strial sculpture. Legs and antennae also smooth and shining.

Pilosity: Short, scattered, yellow hairs on all surfaces of the head and thorax, many of them arising from discernible punctures especially on the vertex, occiput, and petiole. Hairs are longer and more readily visible on the mandibles, front margin of the clypeus, gula, coxae, lateral surfaces of the legs, and particularly the lower surface of the petiole and gaster. Pubescence limited to the funiculi, postpetiole, and gaster, on which areas it merges with the erect hairs so that it is difficult to distinguish one from the other. Pilosity is most abundant on the gaster.

Color: Head, including the mandibles, dark red-brown to blackish brown, the frons, center lobe of clypeus, anterior genae, and center of the occiput, lighter in color; thorax, petiole, and postpetiole red-brown; gaster, legs, and antennae partly yellowish brown.

Holotype: Worker; collected 15 km. east of Tulear, Madagascar, on June 7, 1935 by Harold Kirby (?). Collection notes accompanying it state that the ants were found in a stump and associated with T -[termites?] 4403. Deposited in the author's collection.

Paratypes: Eight other specimens; 4 workers, 1 female (see below), and 3 winged female pupae (1 pigmented), collected from the same nest as the holotype.

Female: Length, 9.09 mm.; head length (excluding mandibles), 1.54 mm.; head width, 1.12 mm.; head index, 0.73; thorax length, 2.67 mm. (dealated).

The female caste is so similar in many ways to the worker in this genus that one is reminded of the parallel situation in ponerine genera. It is, therefore, necessary to point out only the salient features of the queen which separates it from the worker caste. There follows a brief diagnosis.

The female is winged, although the single adult specimen before me had become deaelate, so fully expanded wings for description are lacking. Three pupae, however, have well-developed wing sacs. The female caste differs from the worker by its overall large size, the cephalic and thoracic striae or rugules which are a trifle coarser, the presence of large, flat, oval, compound, eyes at the middle of the sides of the head, composed of a great number of ommatidia (longest diameter of the eye slightly less than the distance from its anterior edge to the insertion of the mandible), three distinct ocelli on the vertex, and the anterior clypeal teeth which are smaller and blunter. A pronounced, arcuate pro-mesonotal suture is present, the mesoscutum has distinct parapsidal furrows, the scutellum is separated by a well-marked suture, and the metanotum is distinguished by deeply impressed boundaries. The epinotum shows the posterior corners rounded (denticles reduced to slight carinae), and the basal face is rounded, passing gradually into the declivity without an angle, the whole segment narrower than in the worker. Petiole and postpetiole are smaller and both are more quadrate than the corresponding segments of the worker, where they are slightly transverse. Dorsal surfaces of both are furnished with fine, curved, transverse striae. The pleurae, and sides of the petiole and postpetiole have enough minute interstrial sculpture to cause a faint dullness to the otherwise shining surface. Pilosity over most of the body is sparser, especially on the gaster. Whether this is natural or due to a worn specimen, it is impossible to tell at present.

In Wheeler's key to the species of Metapone (1919), this ant runs to couplet 5 because of the bluntly bidentate clypeus. At the time this key was produced, there were two species known having the character mentioned, and madagascarica may be distinguished from them in the following manner.

From tillyardi it differs by larger size (6.91 vs. 5.5-6 mm.), a more quadrate petiole which is somewhat more excavated behind, by a rectangular and transverse (rather than oval) postpetiole, and in color which is dark reddish brown to black on thorax and head in contrast to castaneous brown of tillyardi . The head is proportionately longer also (1.38 vs. about 1.25 times as long as broad).

From bakeri it can be separated by a relatively longer head (1.38 vs. less than 1.25 times as long as broad), the presence of five rather than four mandibular teeth, a posterior clypeal suture, striate sculpture of the body (in contrast to smooth), petiole less deeply excised behind, shorter and stouter legs with more inflated femora, red-brown color instead of black, and a difference in size, which is indeed very notable (9.1 vs. 6.4 mm.). It should be stated that these comparisons are between the females of the two species owing to absence of the worker of bakeri which has yet to be discovered. The differences in dentition and in body sculpture however, leave no doubt of the distinctness of these forms.

M. madagascarica is to be distinguished from gracilis , a species which Wheeler described in 1935, again on the basis of the females. It has larger size (9.1 vs. 7 mm.), the ocelli are all nearly the same size, the anterior one being only slightly larger than the laterals in contrast to that of gracilis , antennal scapes almost 3 times as long as broad (not 4 times), and the petiolar node has a concave anterior surface, the dorsal surface weakly convex and from above subquadrate, being only minutely wider than long (1 and 1/3 times longer than broad in gracilis ).

Prom jacobsoni , it differs in larger size (9.1 vs. 6.4 mm.; only the female of jacobsoni has been described), head 1 1/4 times as long as broad instead of 1 1/2, clypeal suture visible, eyes almost in the exact middle of the head, epinotum more than one-half as wide at the rear as at the front, petiolar node 1 1/4 times wider than long ( jacobsoni about 1 1/3 longer than wide), anterior wall of petiole concave, peduncle less than one-half as long as the node, postpetiole a little wider than long (not fully quadrate), and postpetiole with curved, transverse striae rather than shagreened. In many respects the two ants are very similar, to judge from Crawley's description, but the above differences appear to hold and should serve to distinguish them.

From johni it may be told by the shape of the antennal scapes which are broadest in the middle, whereas in johni they are predunculate at the base, broadening apically (or as Karawajew puts it, "ham-shaped" - schinkenartige Form). This situation obtains also in M. greeni . Mandibles have 5 teeth instead of 4, the clypeus is bidentate rather than truncate and feebly concave, and the petiole is less convex dorsally and lacks a tooth posteriorly following the ventral lamella, but the node has sharper and more tooth-like posterior corners. The postpetiole displays a pointed transverse process instead of three, rounded transverse ridges.