Probolomyrmex zahamena

P. zahamena is only known from the type locality, which is a tropical rainforest situated at an elevation of 780 m. All the available material is from a single leaf litter collection. It is surprising that P. zahamena is the only known species found in eastern Madagascar, especially considering the very high leaf litter sampling effort performed by the Malagasy ant project from 1992 to the present. This suggests that the species is either comparatively rare or predominantly hypogaeic.

Identification
Hita Garcia & Fisher (2014) - The following character combination distinguishes P. zahamena from the other two Malagasy species: in full-face view head around 1.4 to 1.5 times longer than broad (CI 67–70); SI 99–102; hind tibia around 1.1 to 1.2 times shorter than head width (HTLI 82–89); petiole relatively shorter, higher and stronger arched, in profile (without ventral process) between 1.0 to 1.2 times longer than high (LPNeI 103–116), in dorsal view petiole around 1.2 to 1.3 times longer than broad (DPeI 76–86).

Probolomyrmex zahamena is fairly distinct and its identification straightforward. The shape of the petiole, which is relatively short, high and stout, distinguishes it clearly from Probolomyrmex tani, while the presence of a metanotal groove separates it from Probolomyrmex curculiformis. In addition, P. zahamena has a slightly broader head (CI 67–70) than the other two (CI 62–66).

Since P. zahamena is only known from one collection event, the observable variation is insignificant.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Nomenclature

 *  zahamena. Probolomyrmex zahamena Hita Garcia & Fisher, 2014: 73, figs. 1C, 2A, B, 5, 6 (w.) MADAGASCAR.

Worker
(N=11). HL 0.64–0.68 (0.65); HW 43–45 (0.44); SL 43–45 (0.44); WL 0.79–0.87 (0.83); PH 0.28–0.33 (0.30); PW 0.33–0.37 (0.34); HTL 0.37–0.40 (0.38); PeH 0.30–0.34 (0.21); PeNH 0.23–0.25 (0.24); PeNL 0.24–0.29 (0.27); PeW 0.20–0.22 (0.21); CI 67–70 (0.68); SI 99–102 (0.100); LMI 34–38 (36); HTLI 82–89 (86); DPeI 76–87 (81); LPeI 79–86 (83); LPeNI 103–116 (109); PeNI 61–67 (62).

In full-face view head between 1.4 to 1.5 times longer than broad (CI 67–70), posterior head margin weakly concave; lateral margins of head convex, broadest medially, posterolateral corners rounded; clypeus and anterior part of frons strongly protruding anteriorly as narrow frontoclypeal, subrectangular shelf or socket; antennal sockets exposed and closely approximated, separated by a thin, vertical lamella formed by fused frontal carinae; mandibles small, triangular to elongate-triangular, masticatory margin armed with one larger apical tooth and a series of six smaller denticles, in full-face view mandibles obscured by frontoclypeal shelf; palp formula 4,2; eyes absent; antennae 12-segmented, funicular antenommeres growing in size and width towards apex without forming well defined antennal club, apical antennomere much larger than remaining funicular antenommeres, antennal scape short (SI 99–102), far from reaching posterior head margin. Mesosoma slender, long, and relatively low (LMI 34–38), in profile mesosomal outline relatively flat; propleurae enlarged and projecting ventrally; promesonotal suture absent; metanotal groove present but weak; declivitous face of propodeum margined by low, obtuse, and concave lamella on each side, propodeal lamella posterodorsally with small, blunt tooth, posteroventrally with rounded lobe; posterior declivity of propodeum weakly concave in dorsal view. Legs long and slender; all tibiae with single, pectinate spur; pretarsal claws simple without median tooth; hind tibia around 1.1 to 1.2 times shorter than head width (HTLI 82–89). In profile petiole with subpetiolar process around 1.2 times longer than high (LPeI 79–86), petiole without subpetiolar process between 1.0 to 1.2 times longer than high (LPNeI 103 - 116), petiolar dorsum strongly arched, much higher posteriorly, anterior face curving smoothly onto dorsum without well developed anterodorsal margin, posterior face vertical and concave, enclosed laterally and dorsally by low, thick carina; in dorsal view petiole around 1.2 to 1.3 times longer than broad (DPeI 76–87); pronotum between 1.5 to 1.7 times longer than petiolar width (PeNI 60–67); subpetiolar process well developed and lamelliform, ventral face weakly concave, anteroventral and posteroventral corners well angled, posteroventral portion slightly sharper but not projecting backwards or dentate. Abdominal segment III in profile narrowed anteriorly, broadest posteriorly. Sting well developed and very long. Surface sculpture very conspicuous, throughout whole body densely foveolate overlaying conspicuous very fine, dense, coriaceous microsculpture. Pilosity strongly reduced throughout and virtually absent, except for few short hairs below frontoclypeal shelf, some longer hairs on mandibles, and some short, fine hairs around metapleural gland orifice. Pubescence whitish, extremely fine, very short, and appressed, present over most of body, funicular antenommeres with such pubescence overlaid by much scattered, much longer, appressed hairs. Colour dark reddish brown, appendages light brown.

Type Material
Holotype, pinned worker, MADAGASCAR, Toamasina, Parc National de Zahamena, Onibe River, 17.75908°S, 48.85468°E, 780 m, rainforest, sifted litter (leaf mold, rotten wood), collection code BLF22214, 21.–23.II.2009 (B.L. Fisher et al.) (: CASENT0914279). Paratypes, ten paratypes with same data as holotype (: CASENT0247390; CASC: CASENT0150894; CASENT0150896; CASENT0150897; CASENT0150898; CASENT0150899; CASENT0150900; CASENT0247389; : CASENT0247391).

Etymology
The new species is named after the type locality, the Zahamena National Park in eastern Madagascar. Zahamena is part of the UNESCO World Heritage Site “Rainforests of the Atsinanana”, and considered as one of the WWF’s Global 200 priority eco-regions for conservation priority. By naming the new species after this locality we want to draw attention to this very important locality with its high conservation value. The species epithet is treated as a noun in apposition, and thus invariant.

References based on Global Ant Biodiversity Informatics

 * Hita Garcia F., and B. L. Fisher. 2014. Taxonomic revision of the cryptic ant genus Probolomyrmex Mayr (Hymenoptera, Formicidae, Proceratiinae) in Madagascar. Dtsch. Entomol. Z. 61 (1): 6576.