Presumably the spiders appeared in the Paleozoic era Carboniferous period. It was about 2-2,5 million years ago. Among the animal kingdom of the spiders are a group of invertebrate creatures. Spiders are the most numerous type of invertebrates – the type of arthropod. As for other classes pertaining to this type, such as insects, crustaceans, millipedes, centipedes, spiders are characterized by segmented limbs and solid chitinous cover, which serves as a exoskeleton.
Among arthropods, spiders belong to the class of arachnids, a detachment of Araneae; other teams in this class include scorpions, false scorpions, spiders, harvestmen, mites, and others. Spiders differ from other arthropods its distinctive appearance and, in addition, numerous species: there are currently known to science about 30 thousand spiders. A majority of spiders come in two suborders: Orthognatha and Labidognatha. In the suborder Orthognatha includes spiders, which are usually called migalomorfami. These spiders are densely covered with hairs and often they are large. Migalomorfy considered primitive mainly due to the structure jaws (chelicerae): claw, they have only the upper jaw and downward. Many migalomorfy live in underground burrows.
Among them: tarantulas (Family Theraphosidae); ktenizidy (family Ctenizidae and Barychelidae); Voronkov spiders (family Macrothgelinae); Spider-diggers (the family Atypidae); All of these spiders live mostly in warm climates. Suborder Labidognatha of a larger group. This includes virtually all other species of spiders known naturalist observers. The presence of claws on both jaws is a common feature that distinguishes this group from migalomorfov. Spiders have suborder Labidognatha, also called Araneomorpha, the respiratory system is present in the trachea, but not lung bags. This includes those spiders that hunt by trapping network, and those who do not need it. Spiders that do not require trapping network is: spiders, crabs (family Thomisidae); wolf spiders (family Lycosidae); spiders horses (family Salticidae); have which is catching -linifidy, spiders, the spider (family Araneidae); daddy-long-legs spiders (family Pholcidae); Webspinner spiders (family Theridiidae); Voronkov spiders (family Agelenidae); within the suborder Labidognatha biologists distinguish two groups: the first includes spiders, which are able to produce a substance called kribellum. It allows you to produce extremely strong web silk. The second group of spiders (and most of them) who have no kribelluma. Learn more about spiders can be read on the site spiders.