Royidris diminuta Bolton & Fisher

Bolton, Barry & Fisher, Brian, 2014, The Madagascan endemic myrmicine ants related to Eutetramorium (Hymenoptera: Formicidae): taxonomy of the genera Eutetramorium Emery, Malagidris nom. n., Myrmisaraka gen. n., Royidris gen. n., and Vitsika gen. n .., Zootaxa 3791 (1), pp. 1-99 : 50-52

Royidris diminuta Bolton & Fisher sp. n.

(Figs 48-50, Map 138)

WORKER (holotype in parentheses). TL 2.8-3.0 (3.0), HL 0.66-0.73 (0.72), HW 0.50-0.58 (0.58), CI 76-81 (81), SL 0.66-0.73 (0.70), SI 121-130 (121), PW 0.34-0.38 (0.37), WL 0.88-0.96 (0.96) (7 measured). EL 0.16-0.18 (EL/HW 0.30-0.32). MfL 0.66-0.76 (MfL/HW 1.25-1.33, MfL/MfH 3.36-3.80).

Matching the description of notorthotenes , and with critical indices falling within the same ranges, but diminuta much smaller in absolute measurements. For comparison of measurements see Table 2.

QUEEN (gyne). Alate when virgin. Very much larger than the worker. TL 6.8, HL 1.25, HW 1.21, CI 97, SL 1.04, SI 86, PW 0.90, WL 2.08, EL 0.36 (EL/HW 0.30), MfL 1.22 (MfL/HW 1.01, MfL/MfH 4.36) (1 measured).

MALE: unknown.

Holotype worker (top specimen of three on pin), Madagascar: Prov. Toliara, Mahafaly Plateau, 6.2 km. 74° ENE Itampolo, 24°39.2'S, 43°59.8'E, 80 m., 21-25.ii.2002, BLF 5814, CASENT0002420, under stone, spiny forest/thicket (Fisher et al.) (CASC).

Paratypes. 2 workers on same pin as holotype, 2 workers with same data but CASENT0002421, 1 worker with same data but CASENT0009802 (CASC).

This small form is separated from notorthotenes with some reservations. In terms of general morphology and critical indices, workers of the two are similar, but in terms of absolute dimensions there is a distinct and persistent gap between them in the ranges of all measurements, with no trace of intermediates. No species of Royidris show any signs of worker dimorphism, but the possibility that the diminuta workers represent the undersized first brood of new foundress queens of notorthotenes cannot be entirely ruled out. An alternative hypothesis, that diminuta , etiolata and notorthotenes constitute a single species, results in a monomorphic species with SI 115-158, an exceptionally broad range. All three species are found in sympatry in the Mahafaly Plateau.

Both series of diminuta , which nests under stones in spiny forest, were included under notorthotenes by Heterick (2006).

Non-paratypic material examined. Madagascar: Prov. Toliara, Mahafaly Plateau, ENE Itampolo (Fisher et al.).