Which of the following statement(s) is/are correct regarding phylum coelenterata? (i) They are aquatic, mostly marine, sessile or free swimming, radially symmetrical animals. (ii) They have a central gastro-vascular cavity with a single opening called hypostome. (iii) Digestion is extracellular and intracellular. (iv) Examples are Sycon, Spongilla and Euspongia.