Spider Spider Spiders (order Araneae) are air-breathing arthropods that have eight legs and chelicerae with fangs able to inject venom. They are the largest order of arachnids and rank seventh in total species diversity among all other 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. , at least 45,700 spider species, and 113 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
Diania as the armoured Lobopodia. These have long been assumed to be related in some way to Arthropoda and it seems likely that arthropods evolved from somewhere within this group. However, all previously discovered lobopodians showed soft, rather ring-like, but not segmented legs. The significance of "Diania" is that it is a lobopodian which appears to have evolved the name-giving character of the arthropods: jointed legs. In the original description of the fossil the authors suggested that "Diania" could be the sister group of "Schinderhannes" and the remaining arthropods, but discussed the possibility that it may be a more primitive form