Tetramorium new species Tanzania

Type location Tanzania; workers only known .

WORKER. Head with weakly convex sides rounding evenly into a shallowly concave occiput; clypeus approximately triangular with a fine median carina and a narrowly rounded posterior margin; the anterior border is very weakly concave, with the median carina slightly but distinctly protruding. Frontal carinae very fine but reaching almost to the occiput, without a discernible scrobe. Antenna 12-segmented but the second funiculus segment is very small; SI 81 with the scape almost reaching the occiput. Mandibles smooth but opaque with reduced dentition. The eyes are quite small and evenly ovoid with 6-7 ommatidia in the longest row. The alitrunk from above has rounded anterior angles and a very fine transverse anterior carina; the metanotal groove is very weakly impressed but clearly visible and has a minute posterior transverse carina; the propodeum is finely but distinctly bordered with small, acute propodeal spines at the angle of the dorsum and declivity; the metapleural lobes are even smaller; the propodeal spiracle is circular with a raised border. In profile the petiole node is quite narrow with a rounded dorsum, from above it is ovoid; the pedicel is as long as the node, with a minute antero-ventral tooth. The postpetiole node is slightly wider but lower than the petiole. The gaster is the same length as the alitrunk; it is both laterally and dorsally ovoid, with a straight anterior margin. The femora and tibiae are quite short and somewhat swollen. The overall sculpturation is of weak reticulation; this is overlaid on the head and alitrunk by very weak longitudinal rugae. The pedicel nodes and the gaster are unsculptured and shiny with a weak opacity. The erect pilosity all over is of quite abundant, fairly long, sharp erect hairs; a distinctive character is that some of the hairs on the pronotum, the petiole and the anterior gaster are angled forwards. The scapes and hind tibia have abundant short semi-erect pilosity.
Amani HQ - TL ca 2.2 mm, HL 0.57, HW 0.47, CI 82, SL 0.42, SI 81, PW 0.36, AL 0.57 (1 measured)
Zigi Lodge - TL 2.1-2.4 mm, HL 0.52-0.53, HW 0.42-0.43, CI 81, SL 0.41-0.42, SI 80, PW 0.35-0.36, AL 0.54-0.55 (2 measured).

In attempting to diagnose this species, the Bolton (1980) key leads one, from step 58, anterior clypeal margin entire, via a fork (dichotomy) at step 82. This separation hinges on the presence or absence of erect hairs and/or pubescence on the dorsal (outer) surface of the hind tibia. The differentiation between - "erect to subdecumbent strong hairs or erect to suberect fine short pubescence, or with both" - and - "any pubescence which is present being decumbent to appressed and generally short" - is, I find, unsatisfactory, especially as Bolton gave no illustration to support this key separation.

One route - via 83, moderate sized eyes; through, 84, long frontal carinae; to, 85, smooth mandibles; takes one to 90 - either a dense fine pelt of moderately long erect hairs on all dorsal surfaces, or, sparse fine short hairs. This species has neither a dense pelt of fine hairs, which would lead via having propodeal teeth to the larger, TL 3.2-3.5 mm, Tetramorium meressei, with a distinctively different backwardly angled postpetiole node; nor does it have only sparse short hairs, which would lead to the, again larger, TL 3.1-3.3 mm, Tetramorium candidum, with which this shares a smooth unsculptured first gastral tergite; candidum lacks distinct propodeal teeth and has a smoothly domed profile to the petiole node.

The second route - via 101, moderate sized eyes; through, 115, fairly short appendages, anterior clypeal margin entire, to, 116, long frontal carinae and SI not more than 100; to 125, propodeal teeth shorter than the metapleural lobes (which these are not); to, 154, SI no more than 100; to, 158, propodeum with a pair of teeth; to, 159, anterior clypeal margin entire; to, 161, first gastral tergite smooth; to, 163, long frontal carinae; and, ending at 165, pronotal dorsum without a coarse median costa, the surface weakly longitudinally rugulose, colour pale yellow, that is the Congo-West Africa species, Tetramorium dumezi which it clearly is not.

The photomontage is of a specimen collected from East Usambara Mts, Tanzania; Amani Nature Reserve Headquarters; S 5°05' E 38°38'; 950 m; Vasily Grebennikov, 12-16.x.2002. Other images can be seen in the folder at -

The photomontage is of a specimen collected from Usambara Mts, Tanzania; Zigi Lodge, Amani Nature Reserve; S 5°05' E 38°38'; 2200 m; Vasily Grebennikov, 9-11.x.2002. Other images can be seen in the folder at -

The photomontage is of a second specimen collected from Usambara Mts, Tanzania; Zigi Lodge, Amani Nature Reserve; S 5°05' E 38°38'; 2200 m; Vasily Grebennikov, 9-11.x.2002.

I have also checked the Bolton (1979) key to Malagasy species but this species cannot be recognised there. Tetramorium scytalum, the only indigenous member, is dark blackish-brown with short stout erect hairs. Tetramorium caldarium has sculptured pedicel nodes, the petiole in profile has a much shorter pedicel and is much blockier. Tetramorium simillimum also is quite different, although the Bolton statement of the "ground sculpture of [the] head between the frontal carinae [being] strongly granular, or reticulate-punctulate, the surfaces matt" appears to be inaccurate, at least as regards African specimens.