Strumigenys lilloana

Identification
Bolton (2000) - A member of the Strumigenys lilloana-group. Only Strumigenys minuscula is also included in this group. The two separate easily as the antenna is 4-segmented, the upper scrobe margin is sinuate and the preocular carina is visible anteriorly in minuscula, whereas the antenna has the usual 6 segments, the head is heart-shaped and the preocular carina is completely concealed by the expanded frontal lobe in lilloana. In addition, in minuscula the head is narrower (CI 86), the dorsolateral margination of the pronotum is hairless behind the humeral angle, and the basigastral costulae arise across the whole width of the first gastral tergite.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Brazil.

Nomenclature

 *  lilloana. Glamyromyrmex (Chelystruma) lilloana Brown, 1950a: 23, fig. 1 (w.) ARGENTINA. Combination in Chelystruma: Kempf, 1959d: 338; in Pyramica: Bolton, 1999: 1672; in Strumigenys: Baroni Urbani & De Andrade, 2007: 122. See also: Bolton, 2000: 201.

Worker
Holotype. Total length 1.91 mm., head length 0.51 mm., alitrunk length 0.47, cephalic index 98, mandibulo-cephalic index 19. Maximum width of pronotum 0.34 mm.

Head broad shield-shaped, broadest at about the posterior third, dorsal surface gently convex in both directions ; posterior excision broadly arcuate, rather shallow. Dorsolateral borders of the head broadly extended and overhanging the deep antennal scrobes. Eyes small, consisting of less than a dozen facets, situated a little behind the midlength of the head astride the ventral borders of the scrobes. Subocular lamina without a tooth anteroventrally.

Antennae short; scapes very faintly S-shaped, a bit more than half as long as the funiculi, slender basally and with the distal 2/3 moderately incrassate, broadest at about the midlength; funiculus short and thick as in other Glamyromyrmex and, related genera, the apical segment equal in length to the remainder of the funiculus; segments I and IV subequal, but the latter much the broadest; II and III subequal, together approximately equaling IV.

Clypeus 1/5 broader than long, weakly convex, its anterior apron projecting and convex, forming a blunt, rounded obtuse angle in the middle anteriorly. Mandibles stout, convex, strongly projecting and apically arched ventrad; outer borders convex in outline. Basal lamella translucent, fairly narrowly rounded, proximal border sloping gently, distal border dropping abruptly to meet the base of the first tooth of the apical series without a diastema intervening; base of lamella about as broad as the space occupied by the first three teeth of the apical series. Apical series of the typical Smithistruma pattern, with 7 long, acute teeth, tooth 3 longest, 4-7 decreasing in length; four rather irregularly fused, subacute denticulae, followed by the long, acute apical tooth, which is about as long as tooth 3 of the principal apical series. At full mandibular closure, opposing apical teeth cross, each projecting laterally for some distance.

Alitrunk with strongly depressed and very sharply marginate dorsum, seen in profile evenly and gently arched from the anterior pronotal border to the posterior mesonotal border. Pronotum broadest anteriorly, 2/3 as broad as the head ; anterior border rounded, cultrate, lateral margins sharp, overhanging the sides, humeral angles bluntly rounded. Mesonotum broad-oval, about half as wide as the pronotum ; promesonotal suture obscure, arcuate; posterior mesonotal border subtruncate, raised slightly above the short, posteriorly sloping dorsal surface of the propodeum. Seen from above, the mesonoto-propodeal constriction strong. Propodeal dorsum short and narrow, continuing the lateral margins onto the propodeal teeth. These teeth diverging behind, lamellate, compressed, about half as long as their inter basal distance; seen from the side acute, translucent, with straight horizontal dorsal borders, continued below as translucent infradental lamellae, each of which widens below to form an angular ventral tooth or plate.

Petiolar peduncle fairly long; posterodorsal disc flattened, marginate anteriorly and laterally, twice as broad as long, with weakly convex surface, the anterior border straight and forming a rather sharp summit if viewed from the side. Sides of node converging behind and each giving rise to a broad, thin, clear, leaf-like lamelliform lobe directed laterally, posteriorly, and deflected a bit below the horizontal, apex narrowly rounded. A band of this same subspongiform material running medially along the midventral line of the petiolar peduncle. Postpetiolar node subrectangular, the posterior border rounded, almost twice as broad anteriorly as long and about 1/3 again as broad as the petiolar node, dorsal surface rather strongly convex; completely surrounded by a thin, vesiculate lamelliform or subspongiform horizontal extension much like the appendages of the petiole in consistency, the transverse anterior border narrow, the lateral lobes sweeping posteriorly and broadening to the anterolateral gastric margins where each ends in an acute apex. Postpetiole below with luxuriant festoons of subspongiform tissue, which meet a spongiform pad on the anteroventral gastric surface. Gaster broad-oval, somewhat depressed above; anterior border transverse, bordered by a thin sinuate lamella. First gastric sternite on each side weakly impressed or concave anteriorly; dorsolateral borders of the first gastric tergite bluntly marginate along the anterior half.

Body in general smooth and highly shining; with very feeble, dilute subreticulation on the cephalic dorsum and weak indications of longitudinal striation on the alitrunk dorsum which do little to interfere with the high polish of the integument. Propodeum, especially the declivity, transversely striate. Basal gastric costulae straight, rather fine and long, extending about half the length of the first gastric tergite, radiating from bilateral sources, with a smooth, narrow median space between the two bundles smooth and shining, as is the remainder of the gastric surface. Legs shining, but antennae and mandibles weakly and densely punctulate, only feebly shining.

Erect pilosity scanty, consisting of erect, straight or slightly curved bristle-like hairs: one pair on the occiput, a pair of curved ones on the humeral angles, three straight ones on each dorsolateral promesonotal margin, a few on the dorsal surfaces of each node, and a more abundant, but still sparse, growth on the gastric dorsum, where they are longest and straightest on the posterior dorsum.

Except for the erect occipital pair, the dorsal cephalic pilosity is reduced to a dilute and very inconspicuous pubescence, closely appressed and anteromedially directed, coarser on the posterior clypeus and becoming very fine and dense along the anterior clypeal border. Legs with abundant, rather long, stout subreclinate hairs; antennae and mandibles densely clothed with short, fine appressed hairs.

Color dark brown; petiole and postpetiole lighter and more yellowish, legs and antennae sordid yellow, appendages of petiole and postpetiole yellowish, of ventral surface of gaster, more whitish.

Paratypes. The four workers sent with the holotype show variation of visible degree only in slight differences of size and proportion. Total length 1.88-2.03 mm., head length 0.51-0.55 mm., alitrunk length 0.46-0.53 mm., cephalic index 96-98, mandibulocephalic index 19-20.

Bolton (2000) - TL 1.9-2.3, HL 0.54-0.56, HW 0.52-0.54, CI 93-100, ML 0.09-0.12, MI 17-22, SL 0.22-0.26, SI 42-48, PW 0.34-0.38, AL 0.50-0.54 (2 measured). The mandibles are fully closed in the few specimens available; shortage of material precludes dissection. However, on the left mandible what appears to be the anterior margin of the basal lamella is just visible in front of the anterior clypeal margin, immediately followed by the tooth row without a diastema. On the right mandible there is a distinct gap or diastema between the basal tooth and anterior clypeal margin. Upper scrobe margins in profile thick behind level of eye, the latter with 5 ommatidia in the longest row. Frontal carinae very broad in full-face view, convex and continuous with the expanded convex fronta1 lobe; the head capsule in this view, excluding the mandibles, strikingly heart-shaped. A single fenestra on each side immediately above the antennal insertion. On postpetiole the lateral lobe extensive and strongly projecting laterally, extensively overhanging the ventral lobe so that the latter is not visible in dorsal view. All waist appendages are more lamellate than spongiform. Discs of petiole and postpetiole in dorsal view both much broader than long and glassy smooth; sides of petiole node converge posteriorly. Disc of postpetiole with anterior margin transverse. Sharp dorsolateral margins of pronotum behind humeri, and lateral marginations of mesonotum, with sparse stiff simple hairs that project dorsolaterally. Petiole, postpetiole and first gastral tergite with short simple standing hairs. Head and body almost entirely unsculptured, here and there with faint superficial reticular patterning on dorsal head and alitrunk; propodeum with 2-3 arched transverse rugulae where dorsum meets declivity. Basigastral costulae present on each side of a clear median strip; longest costulae extend almost half length of tergite.

Type Material
Bolton (2000) - Holotype worker and paratype workers, ARGENTINA: Tucuman, in garden of Instituto Miguel Lillo, 20.iii.1948 (N. Kusnezov) [examined].