Proceratium diplopyx, Brown, W. L., 1980

Brown, W. L., 1980, A remarkable new species of Proceratium, with dietary and other notes on the genus (Hymenoptera: Formicidae)., Psyche 86, pp. 337-346 : 337-342

Proceratium diplopyx new species

Figs. 1, 2.

Holotype worker: TL 6.0, HL (including clypeus) 1.44, HW 1.25, ML (beyond clypeus) 0.15, scape L 1.12, eye diameter 0.12, WL 1.77, petiole L inside view 0.70, gaster L 1.97, hind tibia L 1.26, hind femur L 1.53 mm. CI 87, SI 90. (A single paratype worker hardly differs from the holotype by more than the usual errors of measurement, except that the head is slightly wider: HW 1.29 mm, CI 90.)

Habitus well portrayed in figures 1 and 2. Figure 2 shows the head tilted slightly back from the full-face view plane, so that the posterior cephalic margin appears straight and is slightly surpassed by the scapes laid back in repose. In perfect full-face view, the center of the posterior margin is feebly concave, and the scape laid back does not quite attain it. Median clypeal lobe raised, broad and rounded, with a faint median sulcus and a tendency toward flattening, or even shallow emargination, of the middle of its anterior border, especially as viewed when the head is tilted back. Frontal area narrow-lanceolate and deeply impressed. Eyes each composed of a single, large, clear, convex facet that projects beyond the lateral margins of the head in full-face view.

Mandibles each with 4 sharp teeth, including the apical; because of full closure, the presence of an additional tooth at the basal angle cannot definitely be excluded as a possibility. Labrum retracted against the rest of the under-mouthparts, difficult to see, but appears to be medially sulcate on its visible (extensor) surface and weakly bilobate, with a median excision of its free apical margin. Outside the lateral labral margins can be seen clearly 3 segments of each maxillary palp and 2 segments of each labial palp, so that the palpi must include at least 4 and 3 segments respectively.

Underside of head shallowly concave and weakly rugulose, sunken between thick, rough, raised, ventrolateral cephalic margins ("occipital carinae") that originate near the mandibular insertions.

Antennae with segment II (pedicel) longer than broad; III-VIII about as long as broad to slightly longer than broad; IX-XI slightly broader than long; apical segment about 2 l/2 times as long as broad; the length-breadth ratios vary somewhat in different perpendicular views of the antennal axis.

Trunk as seen from dorsal view weakly pyriform, evenly convex and slightly broader across pronotum (0.94 mm in holotype) than across propodeum and metathorax (0.76 mm), with only a very feeble constriction near truncal midlength, but convexities of mesonotum and propodeum as seen in side-view profile separated by a slight but distinct metanotal impression. Propodeum strongly convex in both directions, passing into declivity through a smooth curve flanked on each side by a short, upturned tooth; declivity smooth and shining, flanked on each side by a low margin bearing a short denticle at the bottom of each concavity, and an upturned, triangular, metapleural tooth or lobe at its ventral extremity.

Propodeal spiracle small, with a nearly round aperture, directed posterolaterad. A curved and rather deep sulcus marks the approximate juncture of propodeum with meso- and metathoracic sclerites below it.

Petiolar node pyriform or subclavate, with feebly suggested peduncle, about 0.47 mm wide across the widest part (near posterior end) in holotype, and about 0.66 mm long. Ventral keel forming an obtuse tooth just behind midlength.

Postpetiole with broadly rounded sides, diverging caudad to the greatest width, a little before the posterior margin (W 0.89 mm in holotype), which is rather sharply constricted. Median posterodorsal surface of postpetiole weakly set off as a high, rounded boss; anteroventral shelf or lip well developed, trailing a short, septate carina caudad.

The remainder of the abdomen forms the most extraordinary structure of this body region known among the ants (figure 1). The second gastric (fourth true abdominal) tergum is grossly hypertrophied posteriad beyond the anteroventral opening, from which issues the true abdominal apex, with the exserted apical segments extending ventro-cephalad. The hypertrophied posterior extension of the second gastric tergum is permanently curled anteroventrad to form a short, bluntly rounded, false gastric apex, so that the real sternum of this segment is externally represented only by a small anteroventral piece, triangular in side view. The incurled ventral surface of the tergal extension is furnished with a series of coarse, sharp rugae that tend to extend vertically or obliquely part way up the lateral surfaces, and run partly transversely across the concavity in the holotype (in the paratype worker, the posterior rugae tend to run lengthwise, following the curve of the curl). From above, the hypertrophied tergum is cylindrical, 1.3 mm long, with almost straight (very feebly concave), parallel sides and a broadly rounded posterior outline, and is almost exactly (0.87 mm) as wide as the postpetiole. (In the paratype, maximum postpetiole W 0.92 mm, maximum second tergal W 0.90 mm.)

In both specimens the gastric apex is extended as 3 stout visible segments and the strong, exserted sting; undoubtedly these are all retractile to some degree.

Legs rather long and slender, though both femora and tibiae are gradually incrassated from base toward apex; hind leg: femur L 1.53, tibia L 1.26, metatarsus L 1.0 mm. Tibial spurs one on each leg (small on mid tibia), pectinate, but only feebly so on mid tibia. Claws on all legs slender, simple.

Head, trunk, petiole and postpetiole densely and moderately coarsely sculptured, opaque generally, but with minor glancing reflections here and there from individual rugulae or the bottoms of punctures. On the head, the sculpture is finest and most shallow, with rugulosity running in the directions shown in fig. 2, and more or less longitudinally on the sides of the head. Mandibles (except for their smooth, shining apices), median clypeus and frontal lobes rather coarsely and unevenly striate. Trunk, petiole and postpetiole densely rugose to scabriculous, becoming scabriculous-muriculate, or even denticulate on propodeum, petiolar node, and both tergum and sternum of postpetiole. Hidden throughout these roughly sculptured surfaces are numerous small but deep punctures with central, piligerous tubercles. The rugae of the postpetiole are longitudinal and subconcentrically curved as seen from above.

Second gastric (fourth true abdominal) tergum predominantly smooth and shining over most of its dorsal, lateral and posterior surfaces, but with numerous, spaced piligerous papillulae throughout, giving way to piligerous punctures caudad, and to the aforementioned rugae ventrad. Apical segments of gaster delicately strigulate, shining. Legs and antennae finely and densely reticulate-punctulate, the antennae distinctly so, and matt; the legs more superficially so, and weakly shining in part. Coxae obscurely rugulose in addition.

Body and appendages covered with an abundant pilosity consisting of fine, curved, tapered, whitish hairs, mostly 0.05 to 0.2 mm long and obliquely standing (straighter and more erect on clypeus, antennae and legs). A short, dense pubescence is also present and widespread, and especially noticeable on antennae and legs, where it is appressed or subappressed and lies longitudinally, and on posterior surface of large gastric tergite, where it is mostly decumbent. Apical gastric segments, especially the last two, with luxuriant bands or brushes of long, fine, pale hairs.

Body color deep reddish-brown, almost mahogany; second gastric (IV abdominal) segment brighter, more reddish; mandibles, antennae, legs and apical gastric segments ferruginous yellow.

Queen, male and larvae still unknown.

Holotype (Museum National d'Histoire Naturelle, Paris) and one paratype worker (Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA) taken in a leaf litter berlesate in "foret dense humide de moyenne altitude" (about 1000 m) at

Iaraka, on the eastern side of the Baie d'Antongil, Province de Tamatave, Malagasy Republic, on 26 November 1969, by J. -M. Betsch.

This altogether extraordinary ant is distinguished at once from its congeners by the strongly produced and downcurved "false apex" of the second gastric segment, as well as by the form of the propodeum, and several minor characters of sculpture, etc. It is the first species of its genus to be taken on Madagascar, and its must be placed in a species group of its own. Its relatively large size, large but singlefacetted eyes, elongate petiole, coarse sculpture and developed propodeal teeth ally it with the stictum group of primitive species more closely than any other group.