Polyrhachis baca

The type collection, the only known material, was found in a degraded dipterocarp forest on a mountain slope.

Identification
A member of the Polyrhachis cyaniventris species-group. Sorger & Zettel (2010) - Polyrhachis baca differs from Polyrhachis cyaniventris in sculpture on mesosoma and gaster; from Polyrhachis pirata in size and colour of mesosoma; and from both species in shape of pronotal spines and setiferation.

Distribution
Only known from the type locality in Central Luzon.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Philippines.

Nomenclature

 *  baca. Polyrhachis (Myrma) baca Sorger & Zettel, 2010: 32, figs. 1-3 (w.) PHILIPPINES (Luzon I.).

Worker
Holotype. TL 8.6 mm, HW 2.00 mm, HL 2.48 mm, CI 81, SL 2.85 mm, SI 142, PSPD 2.44 mm, PPL 0.95 mm, PPW 1.16 mm, PPI 122, PTW2.33 mm, MTL 2.90 mm.

Head with greenish blue shimmer, mesosoma, petiole and gaster with dark bluish shimmer. Legs and antennae with greenish blue shimmer. Head finely puncturated. Venter of head with 10 setae located mostly on outer margins. Vertex with 10 setae. Frons with fine median furrow and 5 setae. Genae without setae (a few setae right on margin with venter not counted). Clypeus on disk with 10 setae. Mesosoma dorsally without setae, microsculpture puncturated. Pronotal spines gracile, in cross-section rather flat, their bases slightly elevated over anterior pronotal disk. Propodeum with dorsal and posterior face separated by almost straight ridge. Sides of propodeum dorsal of stigma with some fine longitudinal rugae overlaying microsculpture. Femora with 4 setae, tibiae without setae. Gaster with isodiametric reticulum and numerous setae (6 on tergite 1, 9 on tergite 2) increasing in length and number towards apex of abdomen.

Type Material
Philippines, Luzon Island, Laguna Province, Los Baños, on northern slopes of Mount Makiling (alternative spelling: Maquiling), Mud Springs (area name), ca. 650 m a.s.l., N 14° 07', E 121°11', in degraded dipterocarp forest. Holotype (worker) labelled "PHILIPPINES, Luzon\ 13 ii 1999, Laguna,\ Los Baños, Mt. Makiling,\ Mud Springs", ca. 650m,\ leg. Schödl (2)".

Etymology
Baca is the Latin word for “pearl,” here used as a noun in apposition. Besides an obvious similarity in subtle metallic shimmer, the name refers to both, the gracile beauty of this species and the unexpected encounter of the single specimen in the Natural History Museum Vienna.