Adult echinoderms are radially symmetrical, while their larvae is bilaterally symmetrical. They are triploblastic and coelomate organisms. The most distinctive feature of echinoderms is the presence of water vascular system which helps in locomotion, capture and transport of food and respiration. An excretory system is absent. Sexes are separate. Reproduction is sexual. Fertilisation is usually external. Development is indirect with free-swimming larvae.