Tetramorium cognatum, Bolton, B., 1979

Bolton, B., 1979, The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Malagasy region and in the New World., Bulletin of the British Museum (Natural History) Entomology 38, pp. 129-181 : 135-136

Tetramorium cognatum sp. n.

(Figs 1, 2)

Holotype worker. TL 2.8, HL 0.66, HW 0.56, CI 85, SL 0.42, SI 75, PW 0.44, AL 0.78.

Mandibles smooth, with scattered small pits. Anterior margin of clypeus with a shallow median impression, the clypeus with a pair of lateral carinae which are at least as strongly developed as the median. Frontal carinae extended back on head by a pair of weak ridges which are almost parallel, very slightly sinuate. Antennal scrobes feeble, scarcely impressed but as long as the scapes, the latter short. Corners of pronotum in dorsal view angular. Metanotal groove feebly impressed with the alitrunk in profile. Propodeum armed with a pair of short triangular spines, the metapleural lobes triangular and larger than the propodeal spines (in some specimens the two are subequal). Node of petiole high and narrow, rounded, in dorsal view slightly broader than long. Dorsum of head and promesonotum finely longitudinally rugulose, the rugulae irregular and tending to meander slightly, the spaces between the rugulae with a fine superficial sculpture of small punctures. Pedicel and gaster unsculptured. Dorsum of head and alitrunk with sparse pubescence and with a number of long, erect hairs (variable on propodeum, usually hairless but some with a single short pair laterad, immediately behind the metanotal groove). First gastral tergite with long and quite dense pubescence but without long hairs such as are seen on the head, alitrunk, and fringing the remaining gastral tergites. Colour mid-brown, the gaster slightly darker.

Paratype workers. As holotype but some more lightly and others more darkly coloured. The petiole node shows some variation and may be as broad as long in dorsal view. The range of dimensions noted is TL 2.5 - 2.8, HL 0.60 - 0.66, HW 0.54 - 0.58, CI 85 - 91, SL 0.36 - 0.42, SI 70 - 75, PW 0.40 - 0.44, AL 0.70 - 0.78 (10 measured).

Holotype worker, Madagascar: Perinei & vic., rain for. rot. wd., 19. iii. 1969, rain forest (W. L. Brown) (MCZ, Cambridge).

Paratypes. 11 workers with same data as holotype; 5 workers and 2 females with same data as holotype but 17. iii. 1969; 2 workers with same data as holotype but 18. iii. 1969 (MCZ, Cambridge; BMNH; MHN, Geneva; NM, Basle).

In the schaufussi-group the cognatum-complex of species is characterized by the lack of pilosity on the first gastral tergite but its retention on succeeding segments. In this complex are severini , proximum , cognatum and naganum . Of these severini is the most conspicuous, being larger than the rest (compare measurements) and having very reduced sculpture on the dorsal alitrunk. The other three species are distinctly smaller and the dorsal alitrunk is strongly rugulose or reticulaterugulose. T. naganum is distinguished by having numerous fine hairs on propodeum and pedicel segments which are absent in the other three members of this complex, although a single pair of fine short hairs is developed laterad immediately behind the metanotal groove in some samples of cognatum . Finally, cognatum is separated from proximum by the presence in the latter of dense short pubescence on the first gastral tergite which is slightly elevated, whilst in the former pubescence is minute, very sparse and strongly appressed.

It is interesting to note that ibycterum of the ranarum-group and latreillei of the tortuosumgroup have paralleled the members of this complex in losing the pilosity of the first gastral tergite, though what advantage is gained by suppressing the gastral hairs cannot be guessed at.

NON-PARATYPIC MATERIAL

Madagascar: no loc (Staudinger); vic. Andasibe (= Perinet) (W. L. & D. E. Brown); Parc Nat. Mont. d'Ambre (W. L. & D. E. Brown); La Mandraka (W. L. & D. E. Brown).