Polyrhachis viola

Nothing is known about the biology of .

Identification
Zettel (2013) - A species of the Polyrhachis (Myrma) cyaniventris-group as defined by Sorger & Zettel (2009). Within this group recognised by combination of small body size (TL 8.1-9.0 mm, HW 1.75-2.02 mm), vivid blue shimmer of body tending to violet on gaster, mesosomal dorsum without setae, gracile and rather flat pronotal spines, distinct longitudinal striation on pro- and mesonotal disk, and relatively short propodeal dorsum (PPI 135-141).

Polyrhachis viola is most similar to Polyrhachis baca from Central Luzon with regard to size, setation and structure of the pronotal spines. It differs from that species by its more vivid metallic shimmer (tending to violet in P. viola and to green in P. baca), the presence of longitudinal striation on the entire dorsum of the mesosoma (restricted to propodeum in P. baca) and anterior third of gastral tergite 1 (absent in P. baca), larger PPI (135-141 vs 122) and by its fine and low transverse propodeal ridge (elevated in P. baca).

Distribution
Known only from two sites in the province of Surigao del Norte, Philippines.

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

Castes
Known only from the worker caste.

Nomenclature

 *  viola. Polyrhachis (Myrma) viola Zettel, 2013: 7, figs. 1-4 (w.) PHILIPPINES.

Worker
Measurements: Holotype: TL 8.3 mm, HW 1.81 mm, HL 2.22 mm, CI 82, SL 2.71 mm, SI 150, PSPD 2.26 mm, PPL 0.82 mm, PPW 1.11 mm, PPI 135, PTW 2.04 mm, MTL 2.76 mm. Paratype with smallest HW: TL 8.1 mm, HW 1.75 mm, HL 2.17 mm, CI 81, SL 2.60 mm, SI 149, PSPD 2.27 mm, PPL 0.79 mm, PPW 1.08 mm, PPI 137, PTW 2.05 mm, MTL 2.58 mm. Paratype with largest HW: TL 9.0 mm, HW 2.02 mm, HL 2.43 mm, CI 83, SL 2.89 mm, SI 143, PSPD 2.55 mm, PPL 0.93 mm, PPW 1.31 mm, PPI 141, PTW 2.22 mm, MTL 2.94 mm.

Body with blue shimmer; tending to violet, most strongly on gaster. Legs slightly darker than head, mesosoma and gaster, antennae almost black. Head finely and densely punctured or reticulate; frons and vertex with fine longitudinal striation in addition. Venter of head with 4 (range 3-12) setae. Vertex with 2 (2-6) setae. Frons with fine median furrow and 8 (5-10) setae. Genae with 0 (0) setae. Clypeus with 8 (6-12) setae on disk. Mesosoma dorsally with 0 (0) setae, longitudinally striate, with dense microsculpture between striation. Pronotal spines gracile, in cross-section rather flat, their bases not elevated above anterior pronotal disk. Propodeum with dorsal and posterior faces separated by almost straight, low ridge. Sides of mesosoma densely punctured, with only traces of very fine longitudinal striation. Gaster with isodiametric reticulum, overlaid in anterior third of tergite 1 by very fine longitudinal striation; number of setae low, tergite 1 with 2 (1-6) setae, tergite 2 with 3 (3-12) setae; setae increasing in length and number towards apex of abdomen.

Type Material
Philippines, Surigao del Sur Province, municipality of Tandag, Mangkagangi Island (N 9°06’ E 126°13’, 0-40 m a.s.l.) off Mindanao Island. Holotype (worker; in University of San Carlos, Cebu City) and six paratypes (currently held in author’s collection and in Natural History Museum Vienna) labelled “Philippines: Surigao d. Sur\ Tandag, Mangkagangi Isl.\ 21.10.2010, leg.\ C.V. Pangantihon (P363)”. One paratype worker labelled “Philippines: Surigao d. Sur\ Lanuza, Sibahay, Magkawas\ Falls 26.10.2010, leg.\ C.V. Pangantihon (P367)” (in author’s collection).

Etymology
The species is named for its colour which resembles that of a violet (or Viola) flower; the epithet is used as a noun in apposition.