Top and bottom view of exoskeleton that make up a Tarantula
Tarantulas show features common to all spiders but also have several unique characteristics that set them apart in their own family. Arachnids, as spiders, scorpions, mites, and their allies are collectively known, are members of the class Arachnida and are not insects (class Insecta). Spiders possess eight legs compared with the six of the insects, the most obvious distinguishing character. Their body is confined in a rigid casing known as an exoskeleton. As the spider grows it must undergo sequential molts, gaining a progressively larger exoskeleton each time. Serious damage to the exoskeleton can have fatal consequences for the spider, and they need to be handled carefully for this reason, although some degree of natural repair (such as regeneration of legs) is possible.
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The body of a tarantula is in two distinct sections (cephalothorax, abdomen) instead of the three sections characteristic of insects (head, thorax, abdomen). The head and thorax are fused together, forming the front segment known as the cephalothorax, which is in turn connected to the abdominal segment of the body. There is a link between the two segments formed by the pedicel. The exoskeleton over the abdomen is thinner, rendering the spider more vulnerable to injury at this point yet permitting some expansion in body size, as for \'example when the female is ready to breed and her abdomen swells with eggs.
The legs of the tarantula are paired and originate under the cephalothorax, almost always with two pairs pointing in a forward direction and two pairs pointing back. Between the front pair of legs the "palps" or "pedipalps" can be seen. These look like legs but attach to the head region rather than further back as do the true legs. The palps serve as a means of distinguishing the sexes and can also be useful in recognizing different species. They are more highly developed in males, being used for mating purposes.