Tetramorium gilgamesh

The preferred microhabitat of T. gilgamesh seems to be leaf litter.

Identification
A member of the Tetramorium naganum-species group. Hita Garcia and Fisher (2014) - The following character combination distinguishes T. gilgamesh from the other members of the T. naganum group: relatively large eyes (OI 25–27); propodeal spines long (PSLI 27–30); petiolar node relatively high and thin, around 1.7 to 2.0 times higher than long (LPeI 50–59); waist segments with several long erect hairs; first gastral tergite with short to moderately long, abundant, decumbent to suberect pilosity, and without short, dense, appressed to subdecumbent pubescence; pilosity appearing disorganized due to varying degrees of inclination and hair length.

The identification of T. gilgamesh within the T. naganum species group is fairly straightforward. The best diagnostic character is eye size since T. gilgamesh has the largest eyes of the group with an OI 25–27 (vs. OI 21–24 in the other four species). Beyond this, it cannot be mistaken for Tetramorium dalek since the waist segments and a first gastral tergite of the latter species are covered with short, comparatively dense, appressed to subdecumbent pubescence without standing pilosity. By contrast, T. gilgamesh has long, erect hairs on the waist segments and the first gastral tergite is covered with short to moderately long, abundant, decumbent to suberect pilosity, but without short, dense, appressed to subdecumbent pubescence. Additionally, the pilosity on the first gastral tergite of T. gilgamesh appears disorganized due to varying degrees of inclination and hair length. The gastral pilosity separates it also from Tetramorium alperti, Tetramorium enkidu, and Tetramorium naganum, which have very different patterns of pilosity/pubescence. Furthermore, T. alperti and T. enkidu have thicker petiolar nodes (LPeI 60–68) than T. gilgamesh (LPeI 50–59). Tetramorium naganum shares the same shape of the petiolar node with T. gilgamesh, and both are also found in sympatry throughout most of their distribution ranges. However, differences in eye size and gastral pilosity distinguish between both species fairly well.

On the basis of the available material it seems that intraspecific variation is generally low in T. gilgamesh.

Key to Tetramorium naganum-group species

Distribution
Tetramorium gilgamesh is distributed in eastern Madagascar. Its distribution ranges from the southernmost known locality Andriantantely north to Montagne d’Anjanaharibe and Montagne d’Akirindro, and northeast to Andranobe and Andampibe on the Masoala Peninsula.

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Habitat
All localities are lowland rainforests situated at elevations of 125 to 600 m.

Nomenclature

 *  gilgamesh. Tetramorium gilgamesh Hita Garcia & Fisher, 2014: 22, figs. 2D, 4A, 8, 61 (w.) MADAGASCAR.

Worker
(N=12). HL 0.52–0.56 (0.54); HW 0.49–0.55 (0.51); SL 0.36–0.38 (0.37); EL 0.13–0.14 (0.13); PH 0.26–0.30 (0.27); PW 0.36–0.41 (0.38); WL 0.61–0.66 (0.64); PSL 0.14–0.17 (0.15); PTL 0.11–0.14 (0.12); PTH 0.21–0.24 (0.22); PTW 0.13–0.17 (0.14); PPL 0.15–0.18 (0.16); PPH 0.19–0.22 (0.20); PPW 0.20–0.24 (0.22); CI 92–98 (94); SI 68–76 (73); OI 25–27 (26); DMI 58–62 (59); LMI 40–45 (42); PSLI 27–30 (28); PeNI 33–40 (37); LPeI 50–59 (55); DPeI 112–127 (118); PpNI 54–59 (56); LPpI 74–85 (80); DPpI 125–142 (132); PPI 143–169 (153).

Worker description. Head weakly to distinctly longer than wide (CI 92–98); posterior head margin weakly 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 distinct but relatively shallow, usually with defined margins all around, but ventral margin sometimes poorly defined and merging with surrounding sculpture, median scrobal carina generally not well developed, if present relatively weak and reaching eye level only. Antennal scapes short, not reaching posterior head margin (SI 68–76). Eyes relatively large (OI 25–27). 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 27–30); 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, around 1.7 to 2.0 times higher than long (LPeI 50–59), anterior and posterior faces not parallel, node slightly narrowing from base to apex, usually anterodorsal and posterodorsal margins situated at about same height (very rarely anterodorsal margin weakly higher than posterodorsal margin), petiolar dorsum weakly to moderately convex; node in dorsal view around 1.1 to 1.3 times wider than long (DPeI 112–127), in dorsal view pronotum between 2.5 to 3.0 times wider than petiolar node (PeNI 33–40). Postpetiole in profile globular, approximately 1.2 to 1.3 times higher than long (LPpI 74–85); in dorsal view between 1.2 to 1.4 times wider than long (DPpI 125–142), pronotum between 1.7 to 1.9 times wider than postpetiole (PpNI 54–59). Postpetiole in profile appearing thicker and lower than petiolar node, postpetiole in dorsal view around 1.4 to 1.7 times wider than petiolar node (PPI 143–169). Mandibles usually unsculptured, smooth, and shining, rarely with traces of longitudinal rugulae; clypeus longitudinally rugose/rugulose, with three 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 eight to nine longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, some rugae irregular, interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured, smooth and shining; lateral head mostly longitudinally rugose to reticulate-rugose, but with extensive unsculptured areas. Ground sculpture on head absent to weakly punctate. Mesosoma laterally and dorsally irregularly longitudinally rugose, sometimes lateral mesosoma with a few unsculptured areas medially. Forecoxae unsculptured, smooth and shining. Ground sculpture on mesosoma usually 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 to moderately long, abundant, decumbent to suberect pilosity, without short, dense, appressed to subdecumbent pubescence; pilosity appearing disorganized due to varying degrees of inclination and hair length. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to subdecumbent hairs. Head, mesosoma, waist segments, and gaster usually orange to light brown, rarely of darker brown, mandibles, antennae, and legs usually lighter, yellowish brown.

Type Material
Holotype, pinned worker, MADAGASCAR, Toamasina, F.C. Sandranantitra, 18.0483°S, 49.0917°E, 450 m, rainforest, sifted litter (leaf mold, rotten wood), collection code HJR101, 18.–21.I.1999 (H.J. Ratsirarson) (: CASENT0247312). Paratypes, four pinned workers with same data as holotype (CAS: CASENT0189097; CASENT0218015); and three pinned workers with same data as holotype except collected from the 21.–24.I.1999 and collection code HJR102 (CAS: CASENT0189096; CASENT0218016).

Etymology
The new species is named after the fictional character “Gilgamesh”, the main figure in the ancient Mesopotamian poem “Epic of Gilgamesh”, one of the earliest surviving works of literature. The species epithet is an arbitrary combination of letters, thus invariant.