Mycetomoellerius pruinosus

Mayhe-Nunes and Brandão (2005) - Gallardo (1916) made detailed observations on this species, summarized as follows: The nests excavated in hard loamy soil had a circular entrance 3 to 4 mm in diameter, surrounded by a low crater of about 10 cm of diameter. Some nests can have a hole small 5 mm tower around the entrance, built with sticks and very fine earth grains used by the ants to make a funnel with borders curved outwards. The internal structure consists on a vertical and cylindrical duct that leads to a first some 5 cm deep chamber with arched roof and an almost flat floor. The other two spherical chambers were found at 10 to 12 cm (second chamber with 4 to 5 cm diameter) and 30 cm depth (third with 5 to 6 cm diameter). The workers are very timid and show stronger activity at sunset, when 5 or 6 workers leave the nest walking slowly, foraging for caterpillar excrements (Oeceticus platensis). Workers in laboratory nest accepted orange pieces as substrate for the fungus. The fungus garden rested on the floor of the chambers, not pending from the chamber roof as in nests of other Trachymyrmex species.

Identification
A member of the Iheringi species group. Mayhe-Nunes and Brandão (2005) - The basal lobe of the antennal scape not enlarged transversely nor very prominent basally or dorsally is the main diagnostic character of M. pruinosus. This species is the only member of the iheringi group that has triangular frontal lobes.

Distribution based on Regional Taxon Lists
Neotropical Region: Argentina, Uruguay.

Nomenclature

 *  pruinosus. Atta (Trachymyrmex) pruinosa Emery, 1906c: 163, fig. 25 (w.) ARGENTINA.
 * Gallardo, 1916b: 249 (q.m.).
 * Combination in Trachymyrmex: Gallardo, 1916b: 248.
 * Combination in Mycetomoellerius: Solomon et al., 2019: 948.
 * Senior synonym of spinosior: Mayhé-Nunes & Brandão, 2005: 294..
 * spinosior. Trachymyrmex pruinosus var. spinosior Santschi, 1922b: 359 (w.) ARGENTINA.
 * Junior synonym of pruinosus: Mayhé-Nunes & Brandão, 2005: 294.

Worker
Mayhe-Nunes and Brandão (2005) - TL 3.4-3.7; HL 1.02-1.09; HW 0.92-1.02; IFW 0.60-0.64; ScL 0.71-0.77; TrL 1.31-1.42; HfL 1.11-1.20. Dark ferruginous brown, some specimens with darker head and gaster, and reddish brown mandibles, legs and tip of funiculus. Integument fine and indistinctly shagreened, opaque. Hairs moderately scarce on the body, short and erect or curved on appendages; hook-like mixed with oblique to decumbent hairs on other parts of body.

Head in full face view little longer than broad (CI 92). Mandible smooth and shining except laterally on base where it is finely transversely striate, and near the masticatory margin, which bears the apical and 7 regularly developed teeth. Frontal lobe triangular, moderately expanded laterad (FLI 64); anterior and posterior borders straight. Frontal carina diverging caudad, reaching the apex of scrobe. Front and vertex with small isolated piligerous tubercles. Posterior third of antennal scrobe clearly delimited by the frontal carina and weakly marked by the extension of the preocular ones. Supraocular projection vestigial. Occiptal corner rounded in full -face view, with many small piligerous tubercles. Occiput notched in the middle. Occipital tooth developed as a stout spine-like projection rather microtuberculated. Inferior occipital corner indistinctly emarginated with weak carina. Eye weakly convex, no more than 12 facets in a row across the greatest diameter. Antennal scape weakly surpassing the occipital corner, when laid back over head as much as possible; basal lobe not enlarged transversely not very prominent basally or dorsally, its anterior face forming an obtuse angle with the superior face of the slender base of the scape; anterior surface surmounted by small tubercles.

Alitrunk. Pronotum with an indistinct humeral angle; antero-inferior corner armed with a triangular and flattened spine-like projection; lateral pines long; median projections as two small microtuberculated spines. Mesonotum with the first pair of projections shorter than pronotal lateral ones; second pair represented by short teeth and the third by one or some minute teeth, forming a small and crenulated longitudinal ridge; mesopleura without hairs; acute triangular projection on superior border of katepisternum. Alitrunk constricted dorso-laterally at the deeply impressed metanotal groove. Basal face of propodeum narrow, laterally delimited by a row of small teeth; propodeal spines longer and slender than promesonotal projections.

Waist and gaster. Petiole shortly pedunculated, the node proper as long as broad with one or two pairs of minute dorsal teeth; subpetiolar process vestigial. Postpetiole slightly broader than long, shallowly excavate above; postero-dorsal border straight; postero-lateral corners without projections. Gaster opaque with minute piligerous tubercles randomly distributed on tergum 1.

Female and male. Gallardo (1916) described and illustrated properly the sexual castes of this species.

Type Material
Mayhe-Nunes and Brandão (2005) - worker; Argentina, Buenos Aires: Tandil.

Probably in Emerys collection; not examined. Two Syntypes workers labeled as “pruinosa var. spinosior (type) XXI.V.d .3418, Cordoba, Cabana, Scott col” in (Dietz personnal communication); One syntype worker of Trachymyrmex pruinosus var. spinosior in, examined.