Tetramorium rigidum

A rainforest species that has been found in litter and rotten wood.

Identification
Bolton (1977) - The very distinctive reticulate-punctate sculpture which fills all the spaces between the rugose sculpture is characteristic of this species and of Tetramorium basum in the ornatum-group. However, basum lacks cross-meshes in the cephalic dorsal sculpture, which are conspicuous in rigidum, and the gaster is basally yellow in basum but unicoloured in rigidum.

Distribution based on Regional Taxon Lists
Indo-Australian Region: New Guinea.

Nomenclature

 *  rigidum. Tetramorium rigidum Bolton, 1977: 108, fig. 28 (w.) NEW GUINEA.

Worker
Holotype. TL 2.9, HL 0.70, HW 0.64, CI 91, SL 0.52, SI 81, PW 0.50, AL 0.86.

Mandibles striate; anterior clypeal margin entire. Frontal carinae long, extending back almost to the occipital margin. Antennal scrobes present but weak, consisting of a shallowly impressed area which extends back beyond the level of the eye in profile and is less strongly sculptured than remainder of head. Maximum diameter of eye c. 0.14. With the alitrunk in profile the propodeal dorsum strongly sloping downwards to the bases of the spines. Propodeal spines long, tapering and acute, feebly downcurved along their length. Metapleural lobes elongate-triangular and acute. Petiole in profile with a long, downcurved peduncle and a relatively high, angular node, the height of the tergal portion of the node greater than its dorsal length. Clypeus with five main longitudinal carinae and in places with traces of other, weaker rugulae between them. Dorsum of head densely longitudinally rugose with numerous conspicuous cross-meshes behind the level of the eyes. Spaces between the rugae packed with a very conspicuous reticulate-puncturation. Area of antennal scrobe reticulate-punctate with only faint traces of rugulae. Dorsal alitrunk reticulate-rugose, the spaces densely reticulate-punctate. Petiole similarly but much less strongly sculptured, both components faint. Sides of postpetiole even more faintly sculptured, the dorsum smooth or with vestiges of sculpture which are almost completely effaced. Gaster unsculptured. All dorsal surfaces of head and body with fine erect or suberect hairs. Dorsal (outer) surface of hind tibiae with very short hairs which are decumbent or appressed. Colour uniform very dark reddish brown, the appendages somewhat lighter.

Paratype. TL 2.8-3.0, HL 0.68-0.76, HW 0.62-0.70, CI 88-92, SL 0.48-0.54, SI 77-81, PW 0.48-0.54, AL 0.84-0.92. Maximum diameter of eye c. 0.13-0.15 (15 measured). As holotype but some paratypes teneral, without full adult coloration.

Type Material
Holotype worker, New Guinea: Papua, Karema, Brown R., 8-Il.iii.I955, no. 564, lowl. rainfor. (E. O. Wilson). Paratypes. 11 workers with same data as holotype; 3 workers with same data as holotype but no. 563; 2 workers as holotype but no. 546 (MCZC; ).