Angelfish

Polyps are millions of tiny animals together and are the most important reef builder. Polyps attach to hard surfaces of the sea floor and form a coral tree. The mouth of the polyp is surrounded by tentacles (Cnidae) full of stinging cells (Nematocytes).
The soft and delicate body of the polyp is protected by a limestone skeleton. The polyps are nourished by tiny algae (Zooxantheliae), which are embedded within the tissue of hard corals. They supply them with up to 98% of their nutritional needs. The tiny algae need the energy of the sun to convert carbon dioxide into oxygen and their skeleton can grow up to 15 cm. per year. Hard coral only live in clear and shallow water. Temperatures below 20 degrees and fresh water can kill the corals so they are not found near coastal areas with excessive run-off.
Corals without zooxantheliae use their stinging tentacles to catch potential prey. Whenever the prey (ranging from plankton to small fish) touches the tentacles, an avalanche of stinging cells is released. These cells penetrate into the victim’s skin and exude a toxin that can paralyze and even kill the prey. This process happens within a few milliseconds and no escape is possible.
Coral reproduction varies depending on the species. Coral colonies mainly grow by asexual division of the polyps, but there is also sexual reproduction. For example; Brain coral and Star coral produce both egg and sperm in one single polyp. Elkhorn coral and Builder coral, produce only sperm or only eggs in separate polyps. Coral spawning is the process in which the egg and sperm are released into the water where fertilization occurs. The result is a larva, which eventually attaches to a hard surface and becomes a polyp.

Soft Coral