recent experiments were published that indicated that although web design was affected adversely in zero gravity conditions, having access to a light source could orient spiders and enable them to build their normally shaped webs under such conditions. Evolution Fossil record Although the fossil record of spiders is considered poor, almost 1000 species have been described from fossils. Because spiders' bodies are quite soft, the vast majority of fossil spiders have been found preserved in amber. The oldest known amber that contains fossil arthropods dates from in the Early Cretaceous period. In addition to preserving spiders' anatomy in very fine detail, pieces of amber show spiders mating, killing prey, producing silk and possibly caring for their young. In a few cases, amber has preserved spiders' egg sacs and webs, occasionally with prey attached; the oldest fossil web found so far is 100 million years old. Earlier spider fossils come from a few lagerstätten, places where conditions were exceptionally suited to preserving fairly soft tissues. The oldest known exclusively terrestrial arachnid is the trigonotarbid Palaeotarbus jerami, from about in the Silurian period, and had a triangular cephalothorax and segmented abdomen, as well as eight legs and a pair of pedipalps. Attercopus fimbriunguis, from in the Devonian period, bears the earliest known silk-producing spigots, and was therefore hailed as a spider at the time of its discovery. However, these spigots may have been mounted on the underside of the abdomen rather than on spinnerets, which are modified appendages and whose mobility is important in the building of webs. Hence Attercopus and the similar Permian arachnid Permarachne may not have been true spiders, and probably used silk for lining nests or producing egg cases rather than for building webs. The largest known fossil spider as of 2011 is the araneid Nephila jurassica, from about , recorded from Daohuogo, Inner Mongolia in China. Its body length is almost 25 mm, (i.e., almost one inch). Several Carboniferous spiders were members of the Mesothelae, a primitive group now represented only by the Liphistiidae. The mesothelid Paleothele montceauensis, from the Late Carboniferous over , had five spinnerets. Although the Permian period saw rapid diversification of flying insects, there are very few fossil spiders from this period. The main groups of modern spiders, Mygalomorphae and Araneomorphae, first appear in the Triassic well before . Some Triassic mygalomorphs appear to be members of the family Hexathelidae, whose modern members