Apterostigma electropilosum

Distribution
This taxon was described from Dominican Amber (Miocene).

Nomenclature

 * † electropilosum. †Apterostigma electropilosum Schultz, 2007: 426, figs. 1, 2 (w.) DOMINICAN AMBER.

Description

 * HOLOTYPE (worker): AMBER: Oligo-Miocene; Dominican Republic; AMNH no. DR-14-984; no other locality data. USNM SIANT database specimen reference number 00443127. Deposited in AMNH. Measurements: head length = 1.06 mm; head width (not including eyes) = 0.68 mm; scape length = 0.99 mm; Weber’s length = 1.37 mm; metafemur length = 1.30 mm.
 * DESCRIPTION: In full-face view, head elongate, evenly rounded at the posterolateral corners and slightly concave at the median posterior border. As in all Apterostigma species, occiput drawn out posteriorly into a “neck” or “collar”; in this species, the collar short, not expanded posteriorly, and lacking integumental rugosities. Frontal carinae strongly produced, extending posterad to well past the level of the eyes. Vertexal carinae not visible, possibly obscured by the amber matrix and by the unusual texture of the integument, discussed below. Vestigial preocular carinae extending posterad to top of eye. Frontal lobes evenly rounded. Antennae with the typical attine number of eleven segments, the apical antennal segment 2.5× as long as the subapical segment, the subapical segment subequal in length to the pedicel. Clypeus clearly with a smooth, shining anterior border, produced medially into a broad, V-shaped angle. Mandibles with eleven teeth, all unusually sharp and showing no wear, teeth decreasing evenly in size toward the mandibular base. Lateral corners of the hypostoma produced into blunt, rounded “hypostomal teeth.” Eyes with six ommatidia across at narrowest circumference (subparallel to the transverse plane) and ten ommatidia across at greatest circumference (subparallel to the longitudinal axis). Eyes prominent and hemispherical, each hemisphere interrupted from behind (i.e., ventrally) by a straight line of occluding integument. Promesonotum with a pair of longitudinal, uniformly low carinae. Anterolateral mesonotal carinae apparently absent and humeral prominences vestigial. Posterior mesonotum with a pair of reduced, very short, almost vestigial carinae (“arista metanotal” of Lattke, 1997), best described as vestigial tubercles. Ventral mesopleural carinae present and complete, but not lamellate. Meso- and metacoxae of typical form, without lamellate or keel-like carinae. Propodeum carinate on the basal and declivous faces, the carinae essentially interrupted extensions of the promesonotal pair. Propodeal spines or tubercles absent, propodeal shoulder evenly rounded. Petiole short and thick, entirely lacking a node; anterior ventral tooth apparently absent. Viewed dorsally, postpetiole roughly as long as broad, and about half as broad anteriorly as posteriorly. First gastral (fourth abdominal) tergite strongly laterally carinate for at least threefourths of its length. Body covered with long, fine, simple, erect setae with a maximum length of 0.15 mm. Integument with a mottled, coarsely granulate texture that interferes with the study of microsculpture. On close inspection, this texture apparently caused by shining bubbles, possibly of an oily secretion, that arose from punctures in the integument while the amber was in a semiliquid state. A similar phenomenon was observed in a modern Apterostigma specimen embedded in Canada balsam by N. A. Weber. The shining clypeal border places this species in the pilosum group (sensu Lattke, 1997), one of two informal subgeneric groupings. The specimen keys out to A. wasmanni (southern Brazil) in Lattke’s (1997) key, but differs from that species in being less strongly sculptured and in having the median clypeal angle more pronounced. In habitus it is similar to many small cryptic species that key out to Lattke’s unrevised “pilosum complex” of species, but is distinct among them in combining evenly rounded frontal lobes, eleven mandibular teeth, and a medially angulate clypeus.
 * ETYMOLOGY: The species name indicates that this is a species of the pilosum group, and probably of the pilosum complex, in amber (electrum).