Soft coral. Corals are small colonial invertebrate animals. Individual polyps may join together to make large structures, which are the basis of coral reefs. Soft corals differ from hard corals in that there is no hard calcium mineral skeleton laid down. Instead the polyps are connected by spongy tubes, which are strengthened by small calcium carbonate fragments called sclerites. Each soft coral polyp has tentacles with which it filters food from the water. Photographed in the Laccadive Sea, Maldives.