Aretidris

The known distribution of the genus shows it is restricted to high elevation sites in the Phillipines. Aretidris nest in rotten logs and forage individually in the leaf litter during the day. They occur at elevations greater than 900 m a.s.l. on the island of Luzon.

Identification
General (2015) - worker: Palp formula: 3, 2. Antennae 12-segmented (including antennal scape) with distinct 3-segmented club. Spur formula: 0, 0. Antennal scrobe absent. In full face view, gena bounded laterally by a longitudinal ridge that runs from dorsal edge of eye to mandibular insertion and is noticeably thickened anteriorly. In full face view, labrum visible below the anterior clypeal margin, even when mouthparts are fully withdrawn into the head. Mandibles with a long narrow basal stem such that a large gap exists between the basal margin of the mandible and the anterior clypeal margin; masticatory margin with a row of 14 small teeth or denticles. In lateral view, promesonotum strongly convex. Entire length of anterior margin of katepisternum produced into a thickened flange, obscuring the posterior margin of procoxa. Metanotal groove strongly impressed. Propodeum convex with a denticle at the junction between the propodeal dorsum and declivity. Petiole sessile. Protuberance or tooth present above and anterior to petiolar spiracle. Petiole slightly larger than postpetiole. Sting long and functional.

Aretidris  is unique among ant genera, with a combination of narrow-based mandibles with a denticulate masticatory margin, gena with a ridge running from the dorsal edge of the eye to the mandibular insertion, palp formula 3 : 2, convex propodeum armed with a denticle, metapleural gland orifice at the apex of the propodeal lobe, and a protuberance over the petiolar spiracle.

This genus shares some similar characters, e.g., bicarinate median clypeus, with Lordomyrma. However, Aretidris  has narrow-based mandibles, a genal ridge, and a convex propodeum, all characters absent in Lordomyrma as currently defined. Lordomyrma , moreover, has an antennal scrobe (present but poorly developed in Lordomyrma furcifera, Lordomyrma infundibuli, and Lordomyrma crawleyi, long frontal carina, and propodeal spines, all characters absent in Aretidris (see Taylor 2009, 2012).

Ward et al. (2015) found Aretidris (as Myrmicine Genus #26 PH02) to be a sister taxon to the genus Vollenhovia in the Crematogastrini. These two genera are not particularly similar morphologically, sharing only a couple of petiolar features: a protuberance over the petiolar spiracle (also found in Gauromyrmex Menozzi, 1933 and Romblonella) and a lack of a petiolar peduncle. That Aretidris and Vollenhovia together are sister to Calyptomyrmex is even more unexpected and problematic. I can find no morphological similarities between Aretidris and Calyptomyrmex.

Aretidris is already included in the myrmicine generic key of General & Alpert (2012), as “Unnamed Genus PH03”. Only a simple substitution of the name is necessary to key it out among the ant genera of the Philippines.

Castes
Known only from the worker caste.

Nomenclature

 *  ARETIDRIS [Myrmicinae: Crematogastrini]
 * Aretidris General, 2015: 132. Type-species: Aretidris buenaventei, by original designation.

Worker
Palp formula: 3, 2. Antennae 12-segmented (including antennal scape) with distinct 3-segmented club. Antennal scrobe absent. Antennal scape weakly incrassate, reaching beyond the posterior margin of head by at least the thickness of the distal part of scape. In full face view, gena with a longitudinal ridge that runs from dorsal edge of eye to mandibular insertion and is noticeably thickened anteriorly. Gena reticulate. Frontal lobes longitudinally striate. Frontal carina short, ending at about mid-length of eye. Clypeus bicarinate; median part narrowly inserted between frontal lobes; anterior margin simple, almost straight, and without an isolated median seta. Labrum visible below anterior clypeal margin, even when mouthparts are fully withdrawn into the head. Mandible smooth, with a long narrowed base such that a large gap exists between the basal margin of the mandible and the anterior clypeal margin, and with 14 small teeth or denticles; apical and subapical teeth largest and the rest diminishing in size posteriad. Posterior margin of head strongly convex. Lateral margin of head converging anteriorly. Eyes located laterally on the head just anterior of the mid-length, and convex, breaking the lateral margin of head. In lateral view, mandibles bent downward apically. Eyes with eight ommatidia in longest axis. Promesonotum and propodeum convex, separated by a prominently impressed metanotal groove. Entire length of anterior margin of katepisternum produced into a thickened flange, obscuring the posterior margin of procoxa. Denticle present where propodeal dorsum meets propodeal declivity. Propodeal spiracle circular, located at least one diameter from edge of declivity. Metapleural gland orifice circular, directed posteriorly (best observed in oblique posterior view), without guard hairs, located at the apex of the propodeal lobe; gland bulla small. Longitudinal ruga present above metapleural gland orifice. Petiole sessile, slightly larger than postpetiole; spiracle below base of anterior face; a protuberance or tooth above and anterior to petiolar spiracle; node rounded, junction of convex petiolar dorsum with anterior and posterior faces indistinct; subpetiolar process absent. Postpetiole slightly flattened dorsally, dorsum forming rounded angles with anterior and posterior faces; subpostpetiolar process present as a low rounded lobe in anterior half of sternite, its anterior margin broadly emarginate in ventral view. First gastral tergite large, about half the total length of gaster. Mesotibial and metatibial spurs absent. Pilosity present as mostly long erect or suberect hairs; shorter erect hairs on coxae; erect hairs on gaster sparse. Color reddish-orange to brown, gaster and appendages lighter; antennal club lighter in color than rest of flagellum and scape.

Etymology
Areté  (ἀρετή, Ancient Greek, excellence) + idris (ἴδρισ, Greek, ant) (WHEELER 1956). Coincidentally, arête (French, ridge) also fits the fact that Aretidris clousei was collected on a low ridge bordering a mountain lake.