Tetramorium plesiarum

 Tetramorium plesiarum has mostly been collected by pitfall trapping and litter sifting suggesting a ground-active lifestyle.

Identification
A member of the Tetramorium plesiarum species group. Hita Garcia and Fisher (2014) - The following character set separates T. plesiarum from the remainder of the species group: smaller species (HW 0.80–1.00; WL 0.92–1.15); eyes of moderate size (OI 21–23); petiolar node high nodiform, not massively enlarged, anterodorsal margin protruding anteriorly and slightly more marginate than posterodorsal margin; petiolar node in profile relatively high and thin, between 1.6 to 1.8 times higher than long (LPeI 56–63), in dorsal view between 1.3 to 1.4 times wider than long (DPeI 131–137); gaster never extremely enlarged and swollen; head without strongly developed and conspicuous reticulate-punctate ground sculpture; mesopleuron and lateral propodeum with moderate punctate ground sculpture; first gastral tergite without strong reticulate-rugose sculpture, usually completely unsculptured, but if sculpture present, then relatively weak and restricted to base of tergite; pilosity on first gastral tergite mostly erect.

Tetramorium plesiarum lacks strong specialisations, such as the strongly sculptured and enlarged gaster of Tetramorium gollum, or the massively developed petiolar node of Tetramorium hobbit. Furthermore, Tetramorium mars has a lower and wider petiolar node (LPeI 69–76; DPeI 108–123) compared to T. plesiarum (LPeI 56–63; DPeI 131–137). The latter also has much less sculpture on the dorsum of the petiolar node. Within the species group T. plesiarum is morphologically most similar to Tetramorium bressleri, and as mentioned in the description of the latter, we have treated them as conspecific through most of the revision The most noticeable difference is certainly body size since T. bressleri (HW 0.80–1.00; WL 0.92–1.15) is much larger than T. plesiarum (HW 0.80–1.00; WL 0.92–1.15). As noted above, there is some slight overlap caused by one large specimen of T. plesiarum and very few small specimens of T. bressleri, but in the main they fit their respective size ranges. Not considering body size, they also differ in eye size and sculpture on mesosoma and waist segments. The eyes of T. plesiarum (OI 21–23) are larger than in T. bressleri (OI 18–19). The mesopleuron and lateral propodeum of T. bressleri is usually mostly unsculptured and relatively smooth and shining, whereas this area is longitudinally rugose with reticulate-punctate ground sculpture in T. plesiarum. Almost the same pattern is seen in the sculpture on the lateral petiolar node as it is significantly more reticulate-punctate and matte in T. plesiarum than in T. bressleri, in which the weak reticulate-punctate ground sculpture appears faintly matte but still relatively smooth and shiny. The sculpture on the sides of the petiolar node varies, too, since it is much more reticulate-punctate and matte in T. plesiarum than in T. bressleri, in which the weak reticulate-punctate ground sculpture looks faintly matte but still relatively smooth and shiny. The shape of the petiolar node in profile is an additional useful character. Finally, in T. plesiarum the anterodorsal margin of the petiolar node protrudes anteriorly and is slightly more marginate than the more rounded posterodorsal margin, contrasting with the shape observed in T. bressleri, in which both margins are usually equally marginate and the anterodorsal margin does not protrude anteriorly at all.

Key to Tetramorium plesiarum-group species

Distribution
Despite being known only from seven localities and fewer than 20 specimens, T. plesiarum has a comparatively large distribution range. However, the populations appear to be relatively disjunctive. The species is known from Andohahela in the southeast of Madagascar and from six additional, more or less scattered localities in the western part of the island ranging from Zombitse and Vohibatsia north through the Makay Mountains, Tsingy de Bemaraha, and Beanka to the Kelifely plateau and Namoroka. (Hita Garcia and Fisher 2014)

Distribution based on Regional Taxon Lists
Malagasy Region: Madagascar.

Habitat
All localities are tropical dry forests, tropical dry forests on tsingy, or gallery forests ranging from 100 to 780 m elevation.

Nomenclature

 *  plesiarum. Tetramorium plesiarum Bolton, 1979: 150, fig. 27 (w.) MADAGASCAR.

Worker
Hita Garcia and Fisher (2014) - (N=12). HL 0.66–0.75 (0.73); HW 0.67–0.76 (0.72); SL 0.45–0.49 (0.47); EL 0.15–0.17 (0.15); PH 0.33–0.44 (0.36); PW 0.50–0.57 (0.53); WL 0.81–0.92 (0.85); PSL 0.16–0.21 (0.18); PTL 0.18–0.22 (0.19); PTH 0.31–0.35 (0.33); PTW 0.23–0.29 (0.26); PPL 0.22–0.26 (0.24); PPH 0.29–0.33 (0.31); PPW 0.32–0.40 (0.35); CI 97–102 (99); SI 64–69 (66); OI 21–23 (22); DMI 60–65 (63); LMI 41–47 (43); PSLI 23–28 (25); PeNI 45–51 (49); LPeI 56–63 (59); DPeI 131–137 (133); PpNI 63–70 (66); LPpI 73–79 (76); DPpI 140–157 (149); PPI 129–143 (136).

Head more or less as long as broad (CI 97–102); posterior head margin weakly concave. Anterior clypeal margin with distinct median impression. Frontal carinae strongly developed and forming dorsal margin of very well-developed antennal scrobes, scrobes moderately to very deep and with clearly defined margins all around; median scrobal carina very well developed and distinctly surpassing posterior eye level, usually ending halfway between posterior eye margin and posterior scrobe margin, often approaching posterior scrobe margin. Antennal scapes short, not reaching posterior head margin (SI 64–69). Eyes small to moderate (OI 21–23). Mesosomal outline in profile weakly to moderately convex, rounded and high (LMI 41–47), moderately marginate from lateral to dorsal mesosoma; promesonotal suture and metanotal groove absent. Propodeal spines elongate-triangular to spinose, moderately long to long, and acute (PSLI 23–28), spines always with broad base and acute tip; propodeal lobes well developed, triangular to elongate-triangular, and acute, always much shorter than propodeal spines. Petiolar node in profile high nodiform, between 1.6 to 1.8 times higher than long (LPeI 56–63), anterodorsal margin situated higher and more angled than posterodorsal, more rounded margin, petiolar dorsum weakly to moderately tapering backwards posteriorly, anterodorsal margin slightly protruding anteriorly, anterior and posterior faces approximately parallel; node in dorsal view between 1.3 to 1.4 times wider than long (DPeI 131–137), pronotum between 1.9 to 2.2 times wider than petiolar node (PeNI 45–51). Postpetiole in profile subglobular, approximately 1.3 to 1.4 times higher than long (LPpI 73–79); in dorsal view around 1.4 to 1.6 times wider than long (DPpI 140–157), in dorsal view pronotum between 1.4 to 1.6 times wider than postpetiole (PpNI 63–70). Postpetiole in profile appearing slightly less voluminous than petiolar node, postpetiole in dorsal view about 1.3 to 1.4 times wider than petiolar node (PPI 129–143). Mandibles unsculptured, smooth, and shining; clypeus longitudinally rugose, with three to five distinct rugae, median ruga better developed than remainder, rugae without cross-meshes; cephalic dorsum between frontal carinae with ten to twelve longitudinal rugae, rugae running from posterior clypeal margin to posterior head margin, often interrupted or with cross-meshes, especially posteriorly; scrobal area mostly unsculptured, relatively smooth and shiny; lateral head longitudinally rugose to reticulate-rugose. Ground sculpture on head usually present but weak. Mesosoma laterally irregularly longitudinally rugose, usually with moderate punctate ground sculpture on mesopleuron and propodeum, dorsal mesosoma longitudinally rugose without any distinct ground sculpture, spaces between rugae smooth and shining. Forecoxae unsculptured, smooth, and shining. Sides of petiolar node and postpetiole with conspicuous, moderate reticulate-punctate ground sculpture, both nodes appearing relatively matte; petiolar node and postpetiole dorsally weakly rugulose/rugose, but mostly unsculptured, and appearing smooth and shining. Gaster usually unsculptured, smooth and shining, sometimes base of first gastral tergite with traces of punctate ground sculpture. Whole body with very abundant, dense, moderately long, and fine standing hairs; first gastral tergite with abundant, long, erect hairs and much scarcer, shorter, decumbent to subdecumbent hairs. Anterior edges of antennal scapes and dorsal (outer) surfaces of hind tibiae with decumbent to suberect hairs. Body of uniform brown, appendages often lighter.

Type Material
Hita Garcia and Fisher (2014) - Holotype, pinned worker, MADAGASCAR, Causse de Kelifely, 17.30306°S, 45.73444°E, forest humus and litter, dry forest, 20.–30.XI.1974 (A. Peyrieras) (: MCZ_Holotype_32372) [examined]. [Note: the GPS data of the type locality was not provided by the locality label or the original description. The data presented above is based on our own geo-referencing of the Kelifely limestone plateau and should be considered an approximation but not the exact position of the type locality.]