Spiders are planets.
Spiders ( order Araneae ) are air-breathing arthropods that have eight legs and chelicerae with fangs that inject venom . They are the largest order of arachnids and rank seventh in total species diversity among all other orders of organisms . , at least 45,700 spider species , and 113 families have been recorded by taxonomists . Unlike most arthropods , spiders have no extensor muscles in their limbs and instead extend them by hydraulic pressure . Venom . Venom is a form of toxin secreted by an animal for the purpose of causing harm to another .