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HOLOTYPE WORKER: TL 3.95, HL 1.02, HW 0.95, CI 93, SL 1.30, SI 137, PW 0.73, ML 0.38. Mandible outer margin strongly curving to a sharp apical tooth, the apex parallel to the anterior clypeal margin. (Holotype with material in mandibles, so mandibles and anterior clypeus described below from paratypes.) Median clypeus tapering and dipping away from the vertex centrally, antennal insertions separated from clypeus by a distance slightly more than the distance from nearest clypeal margin to the clypeal midpoint. In front view, head tapering slightly toward the mandibles, vertex rounded, eyes at upper corners. Bottom margin of eyes located above halfway point of the head and slightly above level of the antennal insertions; their inner margin slightly less than halfway from frontal lobes to sides of the head, their outline breaking the outline of the sides of the head. Antennae 12-segmented, the scape extending beyond the vertex by more than half its length. Mesosoma broad and shallow in profile, sloping rather evenly from the anterior pronotum to the posterior propodeum, a slight depression at the metanotal groove and an even slighter one at the promesonotal suture, propodeal declivity distinct but slight. Petiole about 1.5 times longer than tall, its anterior edge rising only about the same distance as the length of the peduncle, then sloping up for a distance slightly less than the height of the posterior edge. Color: Reddish orange head and mesosoma contrasting against a mostly black gaster. Head even in color, mandibles same shade as the remainder of the head. Mesosoma, legs, and petiole same color as head, although coxae slightly darker. Gaster not entirely black but with four grey stripes made by whitishclear strip along posterior of each gastral tergite; strip is slightly wider than maximum width of the scape. Anterior gastral tergites approach color of mesosoma centrally. Pilosity: Head dominated by recumbent silver hairs interspersed with long, standing hairs on frons and central clypeus. Standing hairs vary in height, but pair closest to vertex as long as maximum width of eyes. Mesosoma with even silver sheen created by recumbent hairs, propodeum with two pairs of long, standing hairs. Petiolar node with four long, backward-pointing hairs arranged in two pairs, one on each side of its highest point; inner hairs slightly shorter than outside ones. Each gastral tergite with about ten long, silver hairs immediately anterior to posterior grey strip. In addition, two adjacent pairs of long hairs lie in line along middle of each tergite. Sculpturing: Head with slight puncturing and body with shallow whorls, but mostly shining.
PARATYPE WORKERS: TL 4.50-5.15, HL 1.23-1.28, HW 1.03-1.13, CI 81-93, SL 1.37-1.42, SI 121- 137, PW 0.82-0.93, ML 0.40-0.47. Five teeth on the masticatory margin visible when the mandibles are closed, declining in size from the apex. Clypeal margin almost straight but curving out slightly. Scapes extending beyond the vertex by a distance less than half their length.
Similar species: The flattened petiole, monochromatic reddish anterior and contrasting black gaster appear unique in this species. Among unidentified collections from Borneo, only two species have a resemblance, but the one closest in coloration has a tall petiole, and the one similar in shape is monochromatic black and overall too narrow.
Given that it has only been collected on Yap Island in Micronesia, it appears to be a poor disperser and could easily be an island endemic.
Etymology: Erythrocephalus is Latin for “red-headed,” which is the distinguishing feature of this species.
Type locality: Yap Island, Yap State, Federated States of Micronesia
Type series: Holotype worker: FSM Yap: Yaptown, Yap I., Mt. Matade (“ No. 1087,” Townes, 12-VII- 1946, NMNH). Paratype workers (2): FSM Yap: Yap I. (Goss, “Jul-Aug” 1950)
Type specimens: Holotype: casent0173108