Dacetinops cibdelus

E.O. Wilson first discovered this species when he found nests of Dacetinops cibdelus in a tract of rain forest at the Busu River, near Lae, New Guinea in 1955.

Identification
Brown & Wilson (1957) - Although from its general habitus this species seems to belong to the Dacetini, a closer look does not bear out placement with that tribe. In the first place, its resemblance is general, and not particular to anyone dacetine genus or subtribe. The shape of the head and mandibles are fundamentally different from those of any dacetine, as is also the arrangement of the spongiform appendages, which at first sight are so dacetine-like. The antennae are ll-segmented, like those of the primitive dacetines, but the distinct club is not a dacetine feature; the palpi of Dacetinops are segmented 2, 2, against 5, 3 for the primitive dacetines and 1, 1 for the higher dacetines. The details of structure of the alitrunk and petiolar node are also not like those of any dacetine, and the sculpture recalls that of the dacetines only at the gastric base, but even here, the costulae are of a basically different type. Ties with the Basicerotini are even fewer, the position of the eyes being one important difference: there seems to be no need to compare further with basicerotines.

The closest similarity holds with the neotropical genus Lachnomyrmex. Lachnomyrmex also has an 11-segmented antenna, but the club is 2-segmented, has no posterior expansion of the head, as in Dacetinops, and the form of the node is somewhat different, as well as the proportions of the parts of the alitrunk. The differences here are not as serious as those between Dacetinops and the dacetines. Dacetinops appears to belong, with Lachnomyrmex, to a group of small myrmicines that includes also the New World Rogeria and Adelomyrmex, as well as the primitive Agroecomyrmex of the Baltic Amber.

Distribution based on Regional Taxon Lists
Indo-Australian Region: New Guinea.

Biology
Brown & Wilson (1957) - The six collections were all made on the forest floor in heavy to medium rain forest. Nos. 978 and 1052 were strays taken from soil-leaf litter berlesates. No. 899 was a stray sample from the forest floor, beneath a log. No. 942 was a small nest in a cavity under the bark of a Zoraptera-stage branch about 6 cm. in diameter, buried in the leaf litter; the queen and two workers were taken. No. 1113 is a queen with one worker, originally taken with a few larvae and two eggs in a small cavity in the middle of a small piece of rotten wood buried in the leaf litter. This apparently incipient colony was kept in an artificial nest for 10 days, but showed no signs of predatory or nest-founding behavior during that time. All of the collections were made during the first three weeks in May, 1955.

From these observations, we may perhaps conclude that D. cibdela is normally a dweller in the leaf litter of the rain forest floor, where it frequently, perhaps usually, nests in or beneath the bark of rotting logs or other large or small masses of rotting wood. Apparently the nests are small in volume and in population, like those of other specialized small myrmicines with similarly slight differences separating the female and worker castes. The workers of this species walk in a slow, deliberate fashion reminiscent of dacetines and basicerotines.

Nomenclature

 *  cibdelus. Dacetinops cibdela Brown & Wilson, 1957: 4, figs. 1-3 (w.q.) NEW GUINEA. Wheeler, G.C. & Wheeler, J. 1957a: 1 (l.). See also: Taylor, 1985: 53.

Worker
Holotype. TL 2.7, HL 0.64, HW 0.59 (CI 91), ML 0.16 (M25), WL 0.76, petiole L 0.22 mm. Index of cephalic depression (ICD) is about 62. Measurements and indices are the ones used in recent works on Dacetini by Brown (see especially Brown, 1953, Amer. MidI. Nat., 50: 7-15).

Form of head and mandibles as shown in Figures 1 and 2. Scrobes sharply defined, each divided partially by a fine anterior carina, and able to receive the entire antenna except the apical part of the club; upper scrobe margins narrowly lamellate. Pronotum margined in front, submarginate along the sides; humeral angles obtuse, but distinct, subtuberculate. Propodeal region of alitrunk short, tapering rapidly behind promesonotum; propodeal declivity weakly concave from side to side, bounded above by an ogival margin, and marginate laterally. Propodeal teeth acute, feebly down-curved toward their apices, their bases separated· by about 4 times their length. Propodeal spiracles not far under the teeth on the lateral margins of the declivity, facing posterolaterad. Petiolar node seen from above approximately as broad as long, with strongly rounded sides, widest near midlength. Postpetiole about half again as broad as long, ellipsoidal or subreniform as seen from above, the more strongly rounded margin posterior. Gaster with a short, straight anterior margin opposite the postpetiole, the sides rounded away on each side.

Spongiform appendages of petiole, postpetiole and gaster finely areolate, apparently composed of cuticular material, not arranged in distinct lobes like those of the dacetines, but narrowed medially below, where masses of opposite sides are joined (Fig. 2).

About 10 coarse, fairly distinct longitudinal costae across the head between the ends of the scrobes, these converging and anastomosing anteriad between the frontal lobes, and joined by short transverse ridges to form a coarse reticulum (not shown in the figures). The bottoms of the large pits or foveolae thus enclosed are sculptured finely and are stibopaque. Disposition of costulae on clypeus shown in Figure 1; interspaces here finely sculptured and subopaque. Underside of head coarsely rugo-reticulate. Mandibles coarsely striate at base, becoming smooth and shining apicad, with scattered punctures. Dorsum of alitrunk with smooth, straight, heavy longitudinal costae running from anterior pronotal margin to the beginning of the propodeal declivity (10 costae across pronotal dorsum), shining and with more or less shining interspaces. Sides of alitrunk and dorsal surface of petiolar node coarsely rugo-reticulate. Basal half of postpetiole and of gaster with coarse longitudinal costae (9-10 across gastric base), remainder of gaster, postpetiole, declivity and concave lateral faces of propodeum smooth and shining, often with scattered punctures. Legs, antennae, scrobes and a band along each side of the first gastric sternum densely punctulate, opaque.

Long, fine, tapered hairs scattered over dorsum of head (those nearest the cephalic borders are shown in Figure 1), alitrunk, both nodes and gaster as well as a few on the gular surface of the head, on the coxae and on the underside of the femora; length ranging about 0.12-0.19 mm. Short, fine, appressed to decumbent hairs forming a pubescence on the legs, antennae and sternum and apex of gaster; similar hairs are sparsely distributed over both surfaces of head, mostly one hair to a foveola, and over mandibles.

Basic body color deep brownish red; mandibles, legs and antennae, especially the club and the first funicular segment, more yellowish.

Total maximum variation for all series: TL 2.2-2.6, HL 0.54-0.63, HW 0.50-0.57 (CI 91-93), ML 0.15-0.16 (MI 24-27), WL 0.65-0.76, petiole L 0.18-0.22 mm. Greatest intranidal variation occurs in series No. 1052: TL 2.2-2.5, HL 0.54-0.62, HW 0.50-0.56 (CI 91-92), ML 0.15 (MI 25-27), WL 0.65-0.75 mm. Very little variation among the workers of these lots. Sculpture, particularly of cephalic dorsum, varies in minor details; spongiform appendages a trifle more voluminous in some specimens than in others.

Queen
Paratypes, dealate. 3 specimens, taken with workers (Nos. 942, 1052, 1113, the last in alcohol, not measured). Deposited in the Museum of Comparative Zoology and elsewhere with the workers. Queen variation (Nos. 942 and 1052): TL 2.6-2.8, HL 0.58-0.62, HW 0.56-0.60 (CI 96-97), ML 0.17-0.19 (MI 29-30), WL 0.79-0.85 mm.

Larva
A single medium larva was preserved in alcohol. This specimen is short and thick, with head turned ventrad. Without proper preparation, none of the details of this larva can be made out, except that the hairs are varied in length, with some of the longer dorsal ones anchor-tipped. This larva has been sent to Dr. G. C. Wheeler for expert study (See Breviora No. 78).

Type Material
Holotype worker (deposited in the Museum of Comparative Zoology) taken in rain forest at the lower Busu River, near Lae, New Guinea (E. O. Wilson leg., No. 1058), May 17, 1955, either as a stray or in berlesate from under bark of a large Zorapterastage log. Three additional workers (paratypes) were taken in this collection and bear the same number.

Paratypes, workers. 9 mounted dry, 3 in alcohol, all collected in the same tract of forest as the holotype (Wilson Nos. 899, 942, 978, 1052, 1058, 1113). Deposited in Museum or Comparative Zoology, U. S. National Museum, Coll. G. C. Wheeler, and one or more each in Australian and European collections as yet unselected.