Mystrium eques Yoshimura & Fisher

Yoshimura, Masashi & Fisher, Brian L., 2014, A revision of the ant genus Mystrium in the Malagasy region with description of six new species and remarks on Amblyopone and Stigmatomma (Hymenoptera, Formicidae, Amblyoponinae), ZooKeys 394, pp. 1-99 : 52-58

Mystrium eques Yoshimura & Fisher sp. n. Figs 18B, 18D, 18F, 21A, 22A, 50A, 51A, 52A, 53A, 54A, 55A, 56A

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. [CASC].

Paratypes.

13 workers: CASENT0317390 [CASC], CASENT0317393 [CASC], CASENT0317394 [CASC], CASENT0317395 [CASC], CASENT0317396 [MSNG], CASENT0317397 [MHNG], CASENT0317398 [BMNH], CASENT0317399 [MCZC], CASENT0317443 [CASC], CASENT0418312 [MNHN], CASENT0418313 [CASC], CASENT0418316 [NHMB], CASENT0418318 [ZMHB]; 5 ergatoid queens: CASENT0418311 [CASC], CASENT0418315 [BMNH], CASENT0418317 [MHNG], CASENT0317391 [MCZC], CASENT0317392 [NHMB], with same data as holotype.

Worker.

Description. 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 Mystrium 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.

Ergatoid queen.

Description. 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.

Male

unknown.

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.

Distribution.

MADAGASCAR: as in Figure 56A.

Additional material examined.

In addition to the type material, specimens from the following localities were examined in this study: MADAGASCAR. Toamasina. Montagne d’Akirindro 7.6 km 341° NNW Ambinanitelo (-15.28833°, 49.54833°), rainforest, 600 m alt.; 5.3 km SSE Ambanizana, Andranobe (-15.66667°, 49.96667°), rainforest, 425 m alt.; Tampolo, Masoala Peninsula, 40.4 km 154° SSE Maroantsetra (-15.73°, 49.96°), rainforest, 30 m alt.; Res. Ambodiriana, 4.8 km 306° Manompana, along Manompana river (-16.67233°, 49.70117°), rainforest, 125 m alt.; Réserve Spéciale Ambatovaky, Sandrangato river (-16.77274°, 49.26551°), rainforest, 450 m alt.; Ile Sainte Marie, Forêt Kalalao, 9.9 km 34° Ambodifotatra (-16.9225°, 49.88733°), rainforest, 100 m alt.; Réserve Speciale Manombo 24.5 km 228° Farafangana (-23.01583°, 47.719°), rainforest, 30 m alt.

Remarks.

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 (as in Fig. 17B); anteromedial portion of the clypeus strongly convex anteriorly (Fig. 18B); and sharper angle between the posterior and dorsal faces of the vertex on the median line (as in Fig. 16A). The queen of Mystrium eques is differentiated from other Mystrium queens by having vestigial wings reduced to small appendages (as in Fig. 25D) with undeveloped wing sclerites (ergatoid), posterior face of the vertex forming approximately a right angle with its dorsal face on the median line (Fig. 21A), and a strongly convex anterior clypeal margin (Fig. 22A).

The worker of Mystrium eques is similar to that of Mystrium oberthueri , however, the strongly convex anterior clypeal margin separates Mystrium eques (Fig. 18B) from Mystrium oberthueri (Fig. 18A), in which the anterior margin of the clypeus is straight. The male of Mystrium eques is not yet known. Because of the similarity between the workers and queens of Mystrium eques and Mystrium oberthueri , we assume the male of Mystrium eques is also similar to that of Mystrium oberthueri . The most easily distinguishable character between workers of Mystrium eques and Mystrium oberthueri , the anterior margin of the clypeus (Figs 18A, B), is unfortunately not useful for males because the anterior clypeal margin and the conical setae on it are less developed in males. Mystrium eques (Fig. 56A) has a sympatric distribution with Mystrium oberthueri (Fig. 56D), so collection locality does not separate these two similar species either. The current male specimens identified as Mystrium oberthueri may contain males of Mystrium eques . Further studies are necessary to resolve this issue.