Tetramorium naganum Bolton 1979

Tetramorium naganum Bolton, 1979 PDF: 136, fig. 7 (w.q.) MADAGASCAR. Malagasy. Primary type information: MADAGASCAR, Toamasina, La Mandraka, 18.912778°S, 47.892222 E 1280 m, montane forest, collection code AB41, 8.II.1977, coll. W.L. & D.E. Brown; CASENT0280584; MCZC AntCat AntWiki HOL

Taxonomic history

See also Hita Garcia & Fisher, 2014c PDF: 26.

(Fig. 7)

Holotype worker. TL 2.8, HL 0.70, HW 0.66, CI 94, SL 0.48, SI 73, PW 0.48, AL 0.78.

Mandibles smooth with scattered pits, without longitudinal striation. Anterior clypeal margin with a median notch or impression. Frontal carinae moderately well developed, extending back almost to the occiput, but becoming confused with the remaining cephalic sculpture before reaching it. Antennal scrobes broad and shallow, without delimited ventral or posterior margins. In full-face view the occipital margin broadly concave, the sides of the head evenly convex and the head narrower in front of the eyes than behind. Dorsal alitrunk in profile evenly convex, the propodeum armed with a pair of straight narrow spines. Metapleural lobes triangular and acute. Node of petiole high and narrow, shaped as in Fig. 7; in dorsal view subglobular, very slightly broader than long. Dorsum of head irregularly longitudinally rugulose, the rugulae fine and widely separated and the interspaces with distinct granular or punctulate ground-sculpture. Dorsal alitrunk covered with irregular fine rugulae which form a disorganized and very broken reticulum, the spaces between them with feeble ground-sculpture which is weaker than on the head. Petiole, postpetiole and gaster unsculptured. Dorsal surfaces of head, alitrunk, petiole and postpetiole with numerous erect fine long hairs and also with scattered pubescence, also erect or suberect . First gastral tergite with abundant subdecumbent pubescence, but without long hairs such as are obvious on the dorsal alitrunk and fringing the remaining gastral segments. Colour orange-brown.

Paratype workers. TL 2.8 - 2.9, HL 0.68 - 0.70, HW 0.62 - 0.66, CI 90 - 94, SL 0.46 - 0.50, SI 73 - 78, PW 0.47 - 0.50, AL 0.70 - 0.78 (11 measured). As holotype.

Holotype worker, Madagascar: La Mandraka, 1280 m, 8. ii. 1977, leaf litter, mont, forest, AB 41 nest in seed capsule in litter (W. L. & D. E. Brown) (MCZ, Cambridge). Paratypes. 16 workers and 1 dealate female, with same data as holotype (MCZ, Cambridge; BMNH).

Among the species of the schaufussi-group which lack long hairs on the first gastral tergite, naganum is unique in having fine long hairs present on the propodeum, petiole and postpetiole. As in cognatum , pubescence on the first gastral tergite is dense and somewhat elevated, not minute, scattered and appressed as in proximum .

Head weakly to distinctly longer than wide (CI 94–99); posterior head margin moderately concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed, diverging posteriorly, and usually approaching or ending at posterior head margin; antennal scrobe present, but weak, shallow, and without defined posterior or ventral margins. Antennal scapes short, not reaching posterior head margin (SI 68–77). Eyes short to moderate (OI 21–23). Mesosomal outline in profile weakly convex, relatively high (LMI 40–45), and moderately to strongly marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines spinose, long, and acute (PSLI 28–33); propodeal lobes short, triangular, and blunt or acute, always much shorter than propodeal spines. Petiolar node in profile high, rounded nodiform, with well-rounded antero- and posterodorsal margins, between 1.7 to 1.9 times higher than long (LPeI 54–58), anterior and posterior faces approximately parallel, anterodorsal and posterodorsal margins situated at about the same height (very rarely anterodorsal margin higher than posterodorsal margin) and equally marginate, petiolar dorsum always convex; node in dorsal view around 1.1 to 1.2 times wider than long (DPeI 107–122), in dorsal view pronotum between 2.7 to 3.0 times wider than petiolar node (PeNI 34–38). Postpetiole in profile globular, approximately 1.2 to 1.3 times higher than long (LPpI 77–84); in dorsal view between 1.2 to 1.4 times wider than long (DPpI 125–137), pronotum around 1.7 to 1.9 times wider than postpetiole (PpNI 52–59). Postpetiole in profile thicker and lower than petiolar node, postpetiole in dorsal view around 1.5 to 1.6 times wider than petiolar node (PPI 147–159). Mandibles variably sculptured, ranging from fully unsculptured, smooth, and shining through partially striate to fully striate; clypeus longitudinally rugose/rugulose, with two to six rugae/rugulae, median ruga always well developed and distinct, lateral rugae/rugulae usually weaker and/or interrupted; cephalic dorsum between frontal carinae with six to nine longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin but very often irregular, interrupted or with cross-meshes, especially posteriorly; scrobal area usually mostly unsculptured, rarely longitudinally rugose to reticulate-rugose; lateral head longitudinally rugose to reticulate-rugose. Ground sculpture on head absent to weakly punctate. Mesosoma laterally and dorsally irregularly longitudinally rugose, rarely lateral mesosoma with a few unsculptured areas medially. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma very weak to absent. Waist segments and gaster completely unsculptured, smooth and shining. Head, mesosoma, and waist segments with numerous, long, and fine standing hairs; first gastral tergite with short, comparatively dense, appressed to subdecumbent pubescence. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae usually with decumbent to suberect hairs. Head, mesosoma, waist segments, and gaster usually orange to light brown, rarely of darker brown, mandibles, antennae, and legs always lighter, usually light yellowish brown.

Tetramorium naganum is found in rainforests or montane rainforests in eastern and north-eastern Madagascar (Fig. 61). The distribution range is disjunctive, very much as in Tetramorium alperti and Tetramorium dalek. Tetramorium naganum is either found in the region around La Mandraka, Analamay, Andranomay, and Andasibe-Mantadia, and Ankerana, or much further north between Anjanaharibe-Sud and the Masoala Peninsula (Ambanizana), with Montagne d’Anjanaharibe being in-between. The reasons behind this discontinuous distribution are not clear yet, but as for Tetramorium alperti, it is likely that Tetramorium naganum was previously much more common in eastern Malagasy humid forests, and present-day populations represent only relict populations. The altitudinal range of the species with 825–1300 m supports this. However, since Tetramorium naganum is not particularly abundant or common where it occurs, it may just be a relatively rare faunal element in eastern Madagascar. If so, further sampling might yield additional material in the future, especially in the geographic areas between the two main populations mentioned above. Like most species in this group, Tetramorium naganum seems to be a leaf litter inhabitant.