Tetramorium plesiarum species group

Based on Bolton and Hita Garcia and Fisher 2011, 2014.

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The T. plesiarum group is a compact assemblage of five species that resemble one another very closely. All are morphologically very conspicuous elements within the Malagasy Tetramorium fauna, and represent arid-adapted species found mostly in the drier western and southern parts of Madagascar. Surprisingly, T. plesiarum, which is much less common than T. bressleri, T. hobbit, and T. mars, is the only member of the species group that was known prior to this revision, and only from the holotype. The other four species, T. bressleri, T. gollum, T. hobbit, and T. mars, are newly described here. All five species share a more or less similar habitus with very well developed antennal scrobes, more or less convex mesosomal profiles, usually medium-sized to long propodeal spines, higher than long and broader than long petiolar nodes, and abundant, long, and often dense pilosity. The species delimitations presented here are mainly based on differences in the shape of the petiolar node and sculpture on different parts of the body. One intriguing feature of the group is the morphological cline observable in the shape of the petiolar node (see Fig. 10), which ranges from massively enlarged and blocky (T. hobbit) through smaller, but still relatively blocky (T. mars), to much higher and thinner (T. bressleri, T. gollum, T. plesiarum).

Hita Garcia and Fisher, 2014. Figure 10.

Tetramorium plesiarum was initially placed in the T. ranarum species group by Bolton (1979) mainly on the basis of petiolar node shape and pilosity. However, in Hita Garcia and Fisher (2012a) we proposed a T. plesiarum species group based on the very conspicuous antennal scrobes present in all species of the group, a character absent in most other Malagasy Tetramorium. We still think that the T. plesiarum species group presents a well distinguishable grouping, although the conspicuous antennal scrobes unfortunately do not separate it from all other Malagasy groups. Several species within the T. ranarum group (e.g. T. zenatum, T. ibycterum, and two additional, yet-undescribed species) also have distinct antennal scrobes, although in these species the margins around the scrobes are much less distinctive and the scrobes themselves shallower than in the T. plesiarum group. However, the species of the T. ranarum group with a scrobe 1) either lack any long, suberect to erect pilosity on the first gastral tergite (T. ibycterum and another undescribed species here listed as T. fhg-bilb), or 2) they have long, subdecumbent pilosity (e.g. one yet-undescribed species listed here as T . fhg-vazi), or 3) if they possess long, standing pilosity, the petiolar node is much longer than broad (T. zenatum). Therefore they cannot be confused with any species of the T. plesiarum group.

Diagnosis

Eleven-segmented antennae; anterior clypeal margin medially impressed; 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 (except in T. gollum); median scrobal carina very well developed and distinctly surpassing posterior eye level, usually ending between posterior eye margin and posterior scrobe margin, often approaching the latter; anterior face of mesosoma weakly developed; mesosomal outline in profile moderately to strongly convex, moderately marginate from lateral to dorsal mesosoma; mesosoma relatively high (LMI 41–56); propodeal spines usually medium-sized to long, elongate-triangular to spinose (PSLI 23–32), rarely short (PSLI 18–20); propodeal lobes usually short, triangular to elongate- triangular, and acute; petiolar node in profile nodiform to high nodiform, in profile between 1.3 to 1.8 times higher than long, (LPeI 56–76), anterior and posterior faces generally parallel, anterodorsal and posterodorsal margins situated at about same height; node in dorsal view typically distinctly wider than long, between 1.1 to 1.5 times (DPeI 108–148); postpetiole much broader than long and transverse, between 1.4 to 2 times broader than long (DPpI 141–200); sculpture on mandibles variably developed; cephalic sculpture distinct, between frontal carinae predominantly longitudinally rugose; mesosoma with well-developed longitudinally rugose sculpture; waist segments weakly to moderately sculptured, never completely unsculptured; first gastral tergite usually with weak ground sculpture at base or completely unsculptured, in T. gollum basal half of tergite strongly reticulate-rugose; whole body with abundant, usually dense, long, and standing hairs; sting appendage spatulate.

References