Metagenesis (alternation of generation) is observed in members of phylum Coelenterata (Cnidaria). Echinoderms are triploblastic and coelomate animals as true coelom is observed in them. Roundworms (Aschelminthes) have organ system level of organization. Comb plates present in ctenophores help in locomotion. Water vascular system is seen in echinoderms, which helps in locomotion, capture and transport of food and respiration.