page_title: Spider
section_title: Mygalomorphae
hierarchical_section_title: Spider / Taxonomy / Mygalomorphae
caption_attribution_description: Čeština: Mexický sklípkan Brachypelma smithi English: Tarantula - (Brachypelma smithi)
context_page_description: Spiders are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species diversity among all orders of organisms. Spiders are found worldwide on every continent except for Antarctica, and have become established in nearly every habitat with the exceptions of air and sea colonization. As of July 2019, at least 48,200 spider species, and 120 families have been recorded by taxonomists. However, there has been dissension within the scientific community as to how all these families should be classified, as evidenced by the over 20 different classifications that have been proposed since 1900.
  Anatomically, spiders differ from other arthropods in that the usual body segments are fused into two tagmata, the prosoma, or cephalothorax, and opisthosoma, or abdomen, and joined by a small, cylindrical pedicel. Unlike insects, spiders do not have antennae. In all except the most primitive group, the Mesothelae, spiders have the most centralized nervous systems of all arthropods, as all their ganglia are fused into one mass in the cephalothorax.
context_section_description: The Mygalomorphae, which first appeared in the Triassic period, are generally heavily built and ″hairy″, with large, robust chelicerae and fangs (technically, spiders do not have true hairs, but rather setae). Well-known examples include tarantulas, ctenizid trapdoor spiders and the Australasian funnel-web spiders. Most spend the majority of their time in burrows, and some run silk tripwires out from these, but a few build webs to capture prey. However, mygalomorphs cannot produce the pirifom silk that the Araneomorphae use as an instant adhesive to glue silk to surfaces or to other strands of silk, and this makes web construction more difficult for mygalomorphs. Since mygalomorphs rarely "balloon" by using air currents for transport, their populations often form clumps. In addition to arthropods, some mygalomorphs are known to prey on frogs, small mammals, lizards, snakes, snails, and small birds.
caption: A Mexican red-kneed tarantula Brachypelma smithi
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