Maotianshan Shales fossil record. Phylum Porifera (sponges; 15 species) and Priapulida (16 species) are also well represented. Other phyla represented are Brachiopoda, Chaetognatha, Cnidaria, Ctenophora, Echinodermata, Hyolitha, Nematomorpha, Phoronida, and Chordata. Possible molluscs include "Wiwaxia" and "Nectocaris". About one in eight animals are problematic forms of uncertain affinity, some of which may have been evolutionary experiments that survived for only a brief period as benthic environments rapidly changed in the Cambrian. Chengjiang is the richest source of the lobopodia, a group including many early panarthropods, with six genera represented: "Luolishania", "Paucipodia", "Cardiodictyon"," Hallucigenia" (also known from the Burgess Shale), "Microdictyon", and "Onychodictyon".
Neuroscience of sleep to have evolved, the functions of sleep should have provided a substantial advantage over the risk it entails. In fact, studying sleep in different organisms shows how they have balanced this risk by evolving partial sleep mechanisms or by having protective habitats. Thus, studying the evolution of sleep might give a clue not only to the developmental aspects and mechanisms, but also to an adaptive justification for sleep. One challenge studying sleep evolution is that adequate sleep information is known only for two phyla of animals- chordata and arthropoda. With the available data, comparative studies have been used to determine