Anthozoans exist as solitary or colonial, and mostly sessile polyps. The polyps are the living part of the coral structure. They are embedded in a hard exoskeleton of calcium carbonate secreted by the external covering of the polyp. To feed the polyp extends its tentacles into the water column. The polyp tentacles contain stinging cells called nematocysts, which catch prey, mainly zooplankton.
Corals reproduce sexually, often in mass spawning events.
Fertilization is external and results in a free swimming planula larvae which disperses the coral through out the sea. The beautiful colours of coral are due to symbiotic relationships with dinoflagellates called, zooxanthallae. The symbiotic relationship means the coral provides a safe home for the zooxanthellae and in-turn the zooxanthellae provides the coral with energy from photosynthesis. So next time you pick up dead coral off the beach, think about the amazing creatures that called the hard skeleton home.