Tetramorium solidum species group

Based on Bolton 1980

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Diagnosis
Antennae with 12 segments. Sting appendage dentiform to elongate triangular. Head massively constructed, HW > 0.80, often exceeding 1.00, equipped with powerful mandibles which are usually strongly sculptured. Anterior clypeal margin at least with a median notch or impression, often with an extensive semicircular emargination which may be very deep. Ventral surface of head usually with very long, conspicuous ammochaete hairs which in most species form a psammophore (absent only in dichroum). Frontal carinae very short or absent, when present ending in front of the level of the anterior margins of the eyes; often terminating just behind the frontal lobes. Antennal scrobes absent. Ventral margin of eye more or less flat, the anterior, dorsal and posterior margins curved so that the eye in profile resembles a reclinate letter D. Metapleural lobes short, low and rounded. Petiole node in dorsal view always broader than long. Pilosity on dorsal alitrunk, pedicel segments and first gastral tergite either absent (solidum-complex) or bizarre (setuliferum-complex), dense only in peringueyi-complex. Dorsal (outer) surfaces of hind tibiae with appressed pubescence in all but peringueyi and dichroum where short erect hairs are present. Base of first gastral tergite sculptured, even if only faintly shagreened; never completely smooth and shining.

Species complexes
The group falls neatly into three complexes of closely related species based on the form of the pilosity which they show.

The first complex includes only peringueyi and dichroum, characterized by an abundant coat of short, stout erect hairs on all dorsal surfaces of the head and body, and also on the legs. Distribution of these hairs separates the two as in peringueyi erect short hairs are present on the antenna} scapes but absent from them in dichroum. T. dichroum is unique in the group as, although elongate hairs are present on the ventral surface of the head, there are no specialized ammochaete hairs.

In the second complex, which includes clunum, galoasanum and setuliferum, erect hairs are absent from the dorsal surfaces of the alitrunk, pedicel segments and first gastral tergite, but instead bizarre appressed pilosity is present. This consists of short, flattened, blunt hairs which are closely appressed to the surface of the sclerite on which they arise and which are usually silvery in colour and glittering in direct light.

The final and largest complex consists of barbigerum, glabratum, grandinode, jordani, pogonion, rufescens, signatum and solidum, in which the body is hairless or nearly so. Only solidum retains a few hairs on the dorsal alitrunk but none of the species have any hairs on the dorsal pedicel segments or the first gastral tergite. This complex also shows the strongest development of the psammophore and has the sculpture of the head and body finer than in other complexes of the group. Of the species included some have very definite diagnostic characters, such as absence of propodeal spines (jordani), presence of one or two pairs of erect fine hairs on the alitrunk (solidum), uniquely shaped pedicel segments (grandinode) or red colour (glabratum, rufescens) as opposed to the uniform black or blackish brown found in most species of the complex. Separation of the remainder rests on characters such as head shape, size of eyes, form of sculpture and overall size.