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Morphology

Basically, the body of an ant is divided into head, alitrunk, petiole and gaster. Some of the major morphological features, which are important for taxonomic studies, are shown in figure 1.


Fig.1
Diacamma ceylonense, showing some of the importantmorphological features used in taxonomy.

The Head

The head varies enormously in shape and size (Figs.2-4). It consists mainly of eyes, clypeus, frons, vertex, genae, antennae and mouthparts. The size and position of the eyes are highly variable. Sometimes the absence of eyes also forms an important identifying character for some species. The mouthparts comprises of mandibles, maxillae, labium and an unpaired labrum. The region bounded anteriorly by the posterior end of the clypeus and laterally by a pair of ridges is the frons. Usually, this is a small and triangular area. The shape, size and the appearance of the frontal area are highly variable and are very important. The region between the vertex and the foramen is the occiput. The portion anterior to the eyes and lateral to the frontal carinae constitutes the gena. Usually, it is divided into two equal halves by a longitudinal suture. In the frontal view, mandibles are articulated usually on the lateral corners of the head and are seen below the clypeus.In some species, the mandibles are articulated in the middle, as in the genus Anochetus. They are very variable in shape, size, and dentition are very much important in ant taxonomy. Other structures like the number of segments on the maxillary and labial palps are of very important in the diagnosis of the species. The number of segments, its relative size, and the nature of antennae also vary greatly with species and are very important. The number of antennal segments varies from 4 12 in workers.

Thorax

Basically, it is formed of prothorax, mesothorax and metathorax (fig.5). The lateral sclerites of the thorax are propleuron, mesopleuron and metapleuron respectively. The metapleuron usually bears a gland, the metapleural gland. But in all ants, in addition to these three segments, the tergite of the first abdominal segment is fused to the thorax and form the propodeum. The thorax varies greatly in shape, size and appearance with sex, castes and with different species. It bears 3 pairs of jointed appendages, the legs and the wings (when present).

Abdomen

This portion in ants is highly specialized and consists of 7 segments. The first segment is fused with the thorax and forms the propodeum. The second segment is always reduced and is separated from the remaining abdominal segments and forms a narrow waist and forms the petiole. Sometimes, the third segment is also reduced and separated to form the postpetiole. The rest of the segments constitute the proper gaster. Each abdominal segment consists of a pair of sclerites, a dorsal tergite and a ventral sternite. In workers, the last abdominal tergite is the pygidium and the last visible sternite is the hypopygium. In all members of the subfamily Formicinae, the apex of the hypopygium gives rise to the acidopore (fig.6). In general, it appears as a short nozzle, usually with a fringe of short setae at its apex. In most formicines the acidopore is always exposed, but in some it may be concealed by the posterior margin of the pygidium. The terminal segment of gaster in females of some species bears an organ of defense, the sting (fig.7).

As per Bolton (1994), ants bear identification characters an all parts of the body, and he says, the area around the clypeus, mandibles and mouthparts is particularly important at the genus and the species rank.

 

 

 

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