Origin and Research Progress of the Coelenterate
Most living diploblasts are marine animals, and scarcely live in fresh water. Nonetheless, the fossil diploblasts are ordinarily found in ocean sediments. Although the most diploblast fossils preserved in post-Cambrian are skeleton building, non-skeletal coelenterates could also be seen as fossils during the Precambrian-Cambrian boundary deposits. In biological evolution history, porous (sponge) animal is only collateral. Meanwhile, coelenterate, representing the onset of eumetazoa, played a key important role in the origin and evolution history of organisms. Therefore, it is prerequisite to study the body plan of coelenterate and their early diversification for understanding the origin of the eumetazoan.