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Metasoma

The "tail" or metasoma consists of five segments and the telson, which is not strictly a segment. The five segments are merely body rings; they lack apparent sterna or terga, and become larger distally. These segments have keels, setae and bristles which may be used for taxonomic classification. The anus is at the distal and ventral end of the last segment, and is encircled by four anal papillae and the anal arch. The tails of some species contain light receptors.

The telson includes the vesicle, which contains a symmetrical pair of venom glands. Externally it bears the curved stinger, the hypodermic aculeus, equipped with sensory hairs. Each of the venom glands has its own duct to convey its secretion along the aculeus from the bulb of the gland to immediately near of the tip, where each of the paired ducts has its own venom pore. An extrinsic muscle system in the tail moves it forward and propels and penetrates with the aculeus, while an intrinsic muscle system attached to the glands pumps venom through the stinger into the intended victim. The stinger contains metalloproteins with zinc, hardening the tip. The optimal stinging angle is around 30 degrees relative to the tip.