Tyrannomyrmex legatus

This rare ant was found in leaf litter in Sri Lanka.

Identification
Tyrannomyrmex legatus is most easily distinguished from Tyrannomyrmex rex and Tyrannomyrmex dux by differences in pilosity, sculpture and the shape of the petiole and postpetiole. T. rex is almost lacking pilosity on the mesosomal dorsum, while the whole dorsal surface is covered with long erect hairs in T. legatus and T. dux. The foveolation is weaker in T. rex, especially on the mesosoma where the foveae on the mesosoma are small with most interspaces equal or wider than their diameter. Tyrannomyrmex legatus can be most easily separated from T. dux by the shape of the petiole, which is much more robust in the former. In lateral view, the peduncle of the petiole is not clearly differentiated, with an abrupt anterior slope of the node. There is also a conspicuous antereoventral projection of the petiole in T. legatus which is absent in T. dux.

Distribution based on Regional Taxon Lists
Oriental Region: Sri Lanka.

Biology
T. legatus was collected by Nihara R. Gunawardene in 2006 from leaf litter in a lowland dipterocarp undisturbed forest in southern Sri Lanka near a stream at the bottom of a slope in the drier period of the year.

Castes
Known from a single worker.

Description
Holotype worker: Sri Lanka, Sinharaja Forest Reserve, N 06˚ 24.697'–N 06˚ 24.823'; E080˚ 25.123'–E 080˚ 24.991', 432m-571m, 25 MAR-07APR 2006, CTFS Plot, Winkler Sacks, N.R. Gunawardene, 15-18. Collection Code ANTC4038.

Holotype deposited in the Museum of Comparative Zoology, Harvard University, Cambridge, Massachusetts, USA.

Worker measurements: HW 0.52, HL 0.72, EL 0.05, SL 0.54, PrW 0.47, ML 0.99, PL 0.35, PPL 0.22, PW 0.29, PPW 0.28, GL 0.76, TL 3.04, CI 72, SI 104.

Description of worker: Head in full face view longer than wide, sides and posterior margins rounded, sides slightly tapering anteriorly. Mandibles triangular, masticatory margin edentate except for two blunt apical teeth, subapical tooth close to and slightly smaller than apical tooth. When mandibles closed, gap at mastigatory margin v-shaped. Palp formula 2, 2. Clypeal anterior margin protrudes above mandibles and is thickened, bearing several straight, stiff hairs, clypeus posteriorly narrowly inserted between frontal lobes. Clypeus lacking carinae, bearing a few irregular shaped foveolae. Frontal lobes present and short but prominent, rounded and obscuring antennal sockets. Antennae 11-segmented with weakly defined three-segmented club, apical segment being largest and entire club equal in length to rest of funiculus, excluding pedicel. Scape somewhat shorter than head length, shallowly curved at base. Eyes small and irregular composed of 4 or 5 poorly defined ommatidia and situated slightly anterior to midlength of head. Mesosoma without mesosomal suture, forming a slightly convex outline in side view. In dorsal view mesosoma is widest in promesonotal area, decreasing in width posteriorly. Anteroventral corner of pronotum rounded. Propodeum armed with two very small, triangular denticles. Propodeal lobes broad and rounded. Petiole without clearly differentiated peduncle, in side view node somewhat thickened and rounded, anterior face less rounded than posterior face, in dorsal view longer than wide. Anteroventral lobe or projection present. Postpetiole wider than long; in dorsal view anterior margin concave and posterior margin convex. First gastral tergite covered with microreticulum fading well before half of its length, remainder of gaster smooth. Middle and hind legs without tibial spurs. All surfaces of the head, mesosoma, petiole and postpetiole completely covered with numerous large round foveolae almost touching each other. Space between foveolae smooth and shiny. Long, stiff, erect, white hairs emerging from the center of each foveola. Abundant erect hairs present on body appendages, including antennal scape as well as funiculus; hairs present on all leg segments and on both dorsal and ventral surfaces of mandibles; those on ventral surface not differing visibly in structure from rest of pilosity. Body color reddish, appendages a lighter reddish color.

Etymology. legatus refers to a military commander appointed by the Roman Senate.