Mycetagroicus,

Brandão, C. R. F. & Mayhé-Nunes, A. J., 2001, A new fungus-growing ant genus, Mycetagroicus gen. nov. with the description of three new species and comments on the monophyly of the Attini (Hymenoptera: Formicidae)., Sociobiology 38, pp. 639-665: 641-644

publication ID

20029

persistent identifier

http://treatment.plazi.org/id/2B410FA1-9662-453D-53D2-127AB9B9D971

treatment provided by

Christiana

scientific name

Mycetagroicus
status

new genus

Mycetagroicus  HNS  new genus

(Figs 1- 24)

Type-species: Mycetagroicus cerradensis  HNS  new species (present designation).

Etymology. From latinized Greek Mycetus (myketus) = fungus: agroikus (agroikos) = of the country, in the sense of cultivation.

Diagnosis (worker). Monomorphic attine ants. All body surfaces covered with regularly spaced, round, minute pits (only seen at higher magnifications, up to 70 times), bearing each a deeply set hair, one third the diameter of the pit (Fig. 4), sometimes effaced by soil particles. Antennal scrobes absent. Each pronotum shoulder in the format of a spinc-like triangular lateral projection (better seen with the pronotum in frontal view, as in Figs 4, 10, 19). Mesonotum without conspicuous projections on the anterior region: the posterior dorsal margin oblique to vertical or nearly so, in lateral view. Petiole compact, petiolar peduncle very short indistinct from node (in lateral view). Postpetiole always larger and broader than the petiole. Disk of tergum I of the gaster covered by a net of coarse rugulae, more evident anteriorly, sometimes joining similar-sized hair pits.

Description (worker). Integument shagreened, opaque. The hair pits and the overall texture of the integument capture fine grained soil particles, that as the workers age, accumulate in a thin uniform mud camouflage layer (Fig. 17). Triangular mandibles longitudinally striate on dorsal surface till the smooth flange from where the teeth arise; the maxillary palps covered by the labrum in all studied specimens, labial palpi two segmented; the mouth apparatus clean of any soil particle, contrary to all other body surfaces (Fig. 23). Clypeus antero-mesially convex, always with a median seta arising from the limit of the anteclypeus and clypeal anterior margin, that bears a small median notch. Preocular carinae start at the level of a rounded projection that interrupts the lateral margin of the head in full face view, evenly curving inwards, ending at the level or behind the posterior margin of the compound eyes, and not reaching the frontal carinae; antennal scrobe absent. Interfrontal width scarcely surpassing one half of its maximum width across the eyes; supraocular projections represented by minute tubercles; occipital margin slightly notched; occipital comers rounded, without noticeable projections but also covered all over by minute tubercles similar to those of the supraocular region; compound eyes notably convex, surpassing the lateral margin of the head and placed anteriorly on the head capsule, closer to the mandibular insertions than to the occipital corners.

Pronotum dorsal and lateral faces meeting in a triangular acute projection (in M. cerradensis  HNS  and M. triangularis  HNS  the anterior and lateral faces ofthe pronotum separated by a carina); antero-inferior corners of the pronotum projected, angulated or ending each in a small blunt tooth; mesonotum without relatively high projections at the anterior dorsal surface, except for low tubercles; posterior face of mesonotum, when seen laterally, oblique or vertical; anepisternum and katepisternum always distinct, sometimes separated by a carina; small metanotum interrupting the dorsal margin ofthe alitrunk; basal face of propodeum with two longitudinal crenulated ridges; the meeting of dorsal and declivitous faces of the propodeum as two short triangular projections, in one species truncated and blunt; metapleura and declivity continuous, without noticeable ridges or carinae. Hind femora length shorter than alitrunk length.

Petiole without conspicuous peduncle and dorsal projections, at most a low posterior triangular tubercle; petiolar ventral process pointing forward, below the metasternum; postpetiole longer, twice as long as the petiole, and large, without dorsal projections; sides almost parallel. Rugulae on the gaster tergum I more conspicuous on the anterior half, the rugulae often linking hair pits to one another; tergum 1 of the gaster at anterior half marginatcd on the sides, sometimes vestigially; sternum I with a longitudinal median sagital carina, as long as half of its length.

Comments. Mycetagroicus  HNS  belongs to an informal group of genera called by authors as the "higher Attini", which includes most of the tribe, and the true leaf-cutting ants, the polymorphic Atta  HNS  and Acromyrmex  HNS  . Among the "higher Attini", the species of Sericomyrmex  HNS  clearly differ from Mycetagroicus  HNS  by the abundant silky pilosity and by the heart-shaped head. Several species of Cyphomyrmex  HNS  (belonging to the two recognized species groups) possess auriculated occipital lobes; workers of the strigatus  HNS  group have relatively deep antennal scrobes, and the frontal lobes of the rimosus  HNS  group species workers are largely expanded laterally. Both Cyphomyrmex  HNS  species groups workers share with Mycetagroicus  HNS  only the presence of a short petiole. The mesonotum of Mycetarotes  HNS  is very thorny; the petiolar node has small but noticeable spines, and its species have occipital projections - characters never observed in Mycetagroicus  HNS  .

In the notebooks of Kempf and Goncalves, we have found samples numbers 1492 and 482 registered as Mycetophylax  HNS  and Mycetosoritis  HNS  , respectively. Unlike the genus we are describing, however, workers of Mycetophylax  HNS  have the whole integument smooth, their dorsal pronotal projections are low and blunt, and the preocular carinae is almost straight. Among the species of Mycetosoritis  HNS  there is a considerable morphological heterogeneity, comparable only to that found in Trachymyrmex  HNS  . Mycetosoritis  HNS  and Trachymyrmex  HNS  differ from Mycetagroicus  HNS  by the presence of an antennal scrobe, and by the presence of tubercles or spines in the dorsum of the gaster.

KEY FOR THE IDENTIFICATION OF SPECIES OF MYCETAGROICUS NEW GENUS (WORKERS):

1. Lateral clypeal projections present (Figs 1-2,5, 11), better seen with head in oblique view; frontal lobes differently shaped; median pronotal projections present or absent; posterior face of mesonotum oblique in side view (Figs 3, 9)................................................... 2

1'. Lateral clypeal projections absent (Figs 17, 20); frontal lobes rounded, their largest width posterior to the antennal insertions, from where they curve inwards, not forming a strong constriction; median pronotal projections present (Figs 18-19); posterior face of mesonotum vertical in side view, with a high median projection (Fig. 18)..................................................................... M. urbanus  HNS  n. sp.

2. Lateral clypeal projections conspicuous (Figs 1-2, 5), flat, narrow, curved inwards with rounded apex; frontal lobes subtriangular, the anterior borders rounded, crenulated, and almost as long as the straight posterior borders; median pronotal projections very short or absent (Fig. 4)............................................... M. cerradensis  HNS  n. sp.

2'. Lateral clypeal projections small, triangular (Fig. 11); frontal lobes rounded, their largest width posterior to the antennal insertions, from where they curve inwards, forming a constriction stronger than in M. urbanus  HNS  (Fig. 8; compare with the Fig. 17); median pronotal projections present (Fig. 9-10)...................... M. triangularis  HNS  n. sp.