Trachymyrmex species groups

These groups are based on numerous revisions that each focused on a single species group.

Cornetzi

Farinosus

Iheringi

based on Mayhé-Nunes & Brandão (2005)

species

Identification

Key to iheringi species group workers

Diagnosis

Antennal scape armed with a remarkable basal lobe. Funicular segments II -VIII as long as broad. Apical part of the antennal scrobe not marked by carinae nor forming prominent tubera. Frontal lobes moderately expanded laterad, the interfrontal width near 2/3 of the head width across the eyes (FLI 58-66). Preocular carina disappearing a little above the eye. Carina of vertex vestigial. Occipital projections always present. Mandible usually with discal area smooth or, as in some specimens of T. iheringi, the grooves are relatively thin and shallow. Superior border of katepisternum always armed with a projection usually triangular or tooth-like, sometimes inconspicuous.

Notes

The first species described in this group, M. iheringi, was proposed in Atta (Acromyrmex) and transferred to Trachymyrmex by Forel (1893), when he proposed the genus as a subgenus of Atta and most recently to Mycetomoellerius by Solomon et al. (2019). Emery's species was unique in the presence of prominent basal lobe at the antennal scape among the other earlier component species of Trachymyrmex cited by Forel (1893): Trachymyrmex saussurei, Trachymyrmex sharpi, and Trachymyrmex septentrionalis. Later, Emery (1906) described another species of the lheringi group, T. pruinosus, as Atta (Trachymyrmex). Despite the general acceptation of this last combination after 1893, Forel (1914) surprisingly proposed T. iheringi var. tucumanus in Acromyrmex (Trachymyrmex). Bruch (1921) also cited Trachymyrmex as a subgenus or Acromyrmex, when he proposed Trachymyrmex tucumanus cordovanus, ignoring its raise to generic rank by Wheeler (1916). In the same year worker redescription and descriptions of alates of T. tucumanus were published by Gallardo (1916) as Trachymyrmex. Since then, all other names of Iheringi species group were proposed in the genus Trachymyrmex. Bolton (1995) correctly stated that the name Trachymyrmex tucumana st cordovana var. missionensis Santschi (1934) is not available.

Lobate antennal scapes is the most notable diagnostic character of the Iheringi group species, shared however with species that belong to the supposed closest genus of Trachymyrmex, Acromyrmex lobicornis and Acromyrmex fracticornis. This character awaits inclusion in a future phylogenetic analysis of the tribe to test its homoplastic condition.

All species of the Iheringi group have frontal lobes moderately expanded laterad, with the interfrontal width close to 2/3 of the head width across the eyes, that seems a common pattern for Trachymyrmex. In the Opulentus group, however, Mycetomoellerius dichrous Kempf has frontal lobes moderately approximate, with the interfrontal width near 1/2 of the head width across the eyes (FLI 51).

Jamaicensis

based on Mayhé-Nunes & Brandão (2007)

Species

Identification

Key to jamaicensis species group workers

Diagnosis

Diagnosis: Monomorphic attine ants with the antennal scrobe margins always reaching and even surpassing the posterior margin of the head; frontal and preocular carinae well marked, subparallel throughout their whole extension, limiting the impressed antennal scrobe; extremities of frontal and preocular carinae always separate and with up to three triangular or rounded compressed tubercles or vertical teeth close to the posterior margin; preocular carina not curved mesad above eyes. Frontal lobes from moderately approximate to moderately expanded laterad, but in most species the interfrontal width near 2/3 of the head width across the eyes (FLI 50–70). Occipital projections (teeth or spines) always present on head. Posterior margin in full-face view smoothly concave, notched in the middle. The paired vertexal carinae indicated by a series of weakly connected piligerous denticles, flanking the shallowly impressed sagital furrow, which in front joins the transverse impression of frons, behind the frontal area. Outer border of mandibles sinuous. Mandibles with discal area smooth and shining, the fine striae confined to the mandibular bases and sides. All funicular segments, including 2nd, longer than broad.

Notes

In Kempf´s sketches of a Trachymyrmex revision deposited in the Museu de Zoologia da Universidade de São Paulo, this group of species was included in the Urichi species group. Like the species that will be treated in the next papers of the series, that belong to the Cornetzi, Urichi and Septentrionalis groups, taxa in the Jamaicensis group lack the main diagnostic characters of the Opulentus and Iheringi groups, respectively the fine silky pubescence on tergum I of gaster and hind femora, and the basal lobe on the antennal scapes (Mayhé-Nunes & Brandão 2002, 2005).

The antennal scrobes of females in species of the Jamaicensis group always reach the posterior margin of the head and end as two separated projections arising from the subparallel preocular and frontal carinae, giving to the scrobe posterior region an “opened” appearance and an angular profile to the posterolateral corners, in frontal view. Although species in the Iheringi group also may present “opened scrobes,” both or at least one of the carinae never attain the posterolateral corners. Two species in the Opulentus group, T. compactus and T. opulentus, have the antennal scrobes’ posterior region projecting as a single protuberance, but these species lacks occipital spines, always present in the females of the Jamaicensis group.

No other Trachymyrmex or even other Attini shows this character state, that we then consider synapomorphic for the group. The Jamaicensis group seems to be restricted to South America north of the Equator, Central America, the Caribbean islands and Florida in the United States of America, except for one species recorded from eastern Brazil.

Opulentus

based on Mayhé-Nunes & Brandão (2002)

species

Identification

Key to Trachymyrmex opulentus species group workers

Diagnosis

Peculiar pilosity, consisting of dense, long, more or less inclined and apically usually not recurved and generally dark hairs, mixed with an extremely low fine and abundant lighter pubescence which is either appressed, or curved or suberect; both types of hairs are evenly distributed on body and appendages, such as in all Sericomyrmex and in some Apterostigma species, although better seen in the apical dorsum of the female hind femora. The midpronotal teeth are lacking or at most vestigial, and the occipital tooth is usually weak and inconspicuous, or sometimes entirely absent. All species of the present group except Mycetomoellerius relictus, have very short and rudimentary propodeal spines.

Notes

Inasmuch as on account of its pilosity, the present species group is closest to Sericomyrmex (Mycetomoellerius opulentuswas originally assigned to this genus), but they can be separated by the features listed above.

All species in the present group share a very impressed frontal area, which is not the case in some species of other groups, although we are not certain for the time being if this is a good defining feature for this taxonomic level.

Three species of the Opulentus group occur in the northern part of South America. taking in consideration that the single known specimen of M. compactus does not allow deriving any comment on the species distribution. Two species, M. opulentus and M. relictus, are widespread in equatorial forests; the first is the only taxon of the group found in Central America. Due to the wide sympatry shown by their know distributions and hence their probable similar environmental demands, the sample of M. relictus from Brazilian savanna (“cerrado”) suggests that M. opulentus may also occur in higher latitudes of the Southern hemisphere. M. dichrous seems to be a typical inhabitant of the vast savannas of central Brazil, although it has also been found in open parkland at Agudos in central Sao Paulo State.

Septentrionalis

Urichi

References