Anemones and Corals: Anthozoa

Anemones and corals aggressively defend their space from neighboring animals of the same and different species. The tentacles used for defense are modified feeding tentacles. Some corals develop sweeper tentacles after prolonged contact with foreign species. These tentacles are five to ten times longer than feeding tentacles and have more stingers. The sweeper tentacles search an area around the coral polyp and cause tissue death in neighboring species on contact. Similar structures in sea anemones are called catch tentacles.

Several species of anemones and corals produce light when an intruder makes contact with the colony. This light may be a bright green flash from a tube or a wave of light across the colony as polyps flash in sequence from the point of contact. The light probably is used to startle predators.

Anemones and corals use asexual (ay-SEK-shuh-wuhl)or sexual reproduction. Sexual reproduction takes place with, and asexual reproduction takes place without, the uniting of egg and sperm and the transfer of DNA from two parents. For asexual reproduction anemone and coral polyps split either lengthwise or crosswise and form two new individuals. In many sea anemones pieces of the base tear off or break free and develop into new individuals. After a free-living larva (LAR-vuh) settles, it transforms into a polyp that repeatedly divides to give rise to additional polyps, all of which remain connected by living tissue. A larva is an animal in an early stage that changes form before becoming an adult. In some species, buds may be released from the polyps of the parent colony, and these then settle and develop a new colony. For many hard corals, damage caused by storms or strong wave action produces fragments that grow into new colonies.

Depending on the species, anemones and corals have separate sexes or have both sexes in the same animal. Anemones and corals lack well-defined sex organs. Rather, the eggs and sperm accumulate in a layer of tissue. The eggs and sperm are shed into the body cavity and are either released through the mouth for fertilization (FUR-teh-lih-zay-shun), the joining of egg and sperm to start development, outside the body, or stay inside the animal for fertilization inside the body with release of the embryos through the mouth at a later time. Embryos of anemones and corals develop into larvae (LAR-vee) that may or may not feed and that can stay in open water for days to weeks.

One of the most spectacular behaviors of anemones and corals is the simultaneous release of sperm and eggs by many colonies over a wide area of coral reef. During these mass spawning events, huge slicks of eggs and sperm and developing larvae can be seen on the water surface, attracting a variety of predators that feed on the spawned eggs.