Mystrium eques

Identification
Yoshimura and Fisher (2014) - The worker of Mystrium eques is easily distinguished from those of other Mystrium species by a combination of the following characters: strong and deep longitudinal sculpture on the dorsal and lateral surface of pronotum; anteromedial portion of the clypeus strongly convex anteriorly; and sharper angle between the posterior and dorsal faces of the vertex on the median line. The queen of M. eques is differentiated from other Mystrium queens by having vestigial wings reduced to small appendages with undeveloped wing sclerites (ergatoid), posterior face of the vertex forming approximately a right angle with its dorsal face on the median line, and a strongly convex anterior clypeal margin.

The worker of M. eques is similar to that of Mystrium oberthueri, however, the strongly convex anterior clypeal margin separates M. eques from M. oberthueri, in which the anterior margin of the clypeus is straight.

Distribution based on type material
Madagascar.

Nomenclature

 *  eques. Mystrium eques Yoshimura & Fisher, 2014: 69, figs. 18B, 18D, 18F, 21A, 22A, 50A, 51A, 52A, 53A, 54A, 55A, 56A (w.eq.) MADAGASCAR.

Worker
Measurements: holotype. HL 1.78, HW 1.65, SL 1.23, ML 1.87, HD 1.08, WL 2.01, PnW 0.94, PpW 0.83, PtW 0.85, PtL 0.57, CI 92.6, SI 74.4, MI 113.8, PpI 88.6, PtI 150.4.

HL 1.72–2.11, HW 1.59–2, SL 1.26–1.42, ML 1.81–2.18, HD 1.08–1.33, WL 2.07–2.34, PnW 0.92–1.1, PpW 0.83–1.02, PtW 0.83–1.03, PtL 0.54–0.67, CI 91.4–97.3, SI 70.4–78.9, MI 107.4–114.2, PpI 84.7–92.7, PtI 149.5–161.2 (10 specimens measured).

Posterolateral corner of head strongly to moderately expanding posteriorly. Posterior face of vertex forming almost a right angle with dorsal face on median line of head, so that declivity of vertex on lateral part as steep as that on median part. Whole region of vertex finely striated. Eye relatively smaller than that of M. oberthueri. Anterior margin of clypeus strongly convex with long conical setae. Genal tooth of head relatively long, as long as lateral lobe of clypeus. Masticatory margin of mandible almost invisible in full-face view. Width of dorsal surface of mandible on distal portion slightly wider than that on mandibular shaft. Second maxillary palpomere longer than third. First flagellomere (third antennal segment) as long as pedicel (second antennal segment). Strong, deep and thick longitudinal striae regularly impressed on whole central part of pronotal dorsum. Strong, deep, and thick longitudinal striae impressed on lateral surface of pronotum. Mesonotum differentiated from propodeum in dorsal view, length slightly shorter than that of propodeum. Metanotal groove shallowly and gently impressed, and mesonotum higher than pronotum in lateral view. Metapleural gland bulla moderately developed, and propodeal declivity in lateral view almost straight. Petiole widened on posterior 1/4 and gently narrowed anteriorly in dorsal view, anterior margin straight to gently rounded and sometimes edged by thin striae.

Body color blackish brown. Appendages brighter, and four distal segments of antennal club yellowish.

Queen
Ergatoid Measurements: HL 1.48–1.62, HW 1.41–1.57, SL 1.10–1.25, ML 1.38–1.56, HD 0.99–1.09, WL 1.95–2.10, PnW 0.85–0.95, PpW 0.83–0.94, PtW 0.87–0.97, PtL 0.52–0.56, CI 94.0–97.2, SI 77.7–83.9, MI 93.2– 107.0, PpI 93.8–101.6, PtI 160.5–172.6 (7 specimens measured).

Wings vestigial and forming small but distinct appendages. Wing sclerites undeveloped. Posterolateral corner of head strongly expanding posteriorly, expansion relatively weaker than that of workers. Posterior face of vertex forming almost a right angle with dorsal face on median line of head, so that declivity of vertex on lateral part as steep as on median part. Ventral half of vertex sculptured. Eye small but distinct. Ocelli absent. Anterior margin of clypeus distinctly convex with long to short conical setae. Anterolateral portion of head with short spine. Masticatory margin of mandible almost invisible in full-face view. Dorsal surface of mandible on distal portion slightly wider than that on mandibular shaft. Spatulate or narrow spoon-shaped seta present on basal side of each basal denticle on masticatory margin of mandible. First flagellar segment on antenna about 1.0–1.2× length of pedicel. Setae on pronotum distinctly spatulate, widened distally with sharp or blunt apex. Metapleural gland bulla moderately developed, not expanding to dorsum of propodeal spiracle, so that propodeal declivity in lateral view weakly convex and rounded posteriorly on its ventral 1/3. Petiole relatively long in dorsal view, about 1.0–0.8× length of abdominal segment III.

Body color blackish to reddish brown.

Type Material
Holotype. Worker: CASENT0418314, BLF04691, MADAGASCAR, Toamasina, Tampolo, Masoala Peninsula, 40.4 km 154° SSE Maroantsetra (-15.73°, 49.96°), 30 m alt., 28.xi.–3.xii.2001, B.L.Fisher & H.J.Ratsirarson leg. ]. Paratypes. 13 workers: CASENT0317390 CASC, CASENT0317393 CASC, CASENT0317394 CASC, CASENT0317395 CASC, CASENT0317396 MSNG, CASENT0317397, CASENT0317398 , CASENT0317399 , CASENT0317443 CASC, CASENT0418312 MNHN, CASENT0418313 CASC, CASENT0418316 , CASENT0418318 ; 5 ergatoid queens: CASENT0418311 CASC, CASENT0418315 BMNH, CASENT0418317 MHNG, CASENT0317391 MCZC, CASENT0317392 NHMB, with same data as holotype.

Etymology
This species name is the Latin word eques, inspired by the distinctly developed clypeus (shield) on the new species. The species epithet is a noun and invariant.