Zoanthid

Zoanthids are soft corals that live in colonies as single polyps attached to a base made of a mass of tissue or pieces of sediments, sand, and rock. The zoanthid coral can be many different varieties of colors and the colonies have distinct shapes. The zoanthids appear to be quite adaptable and are found all around the world, but since they need sunlight to survive they are only found in the shallow areas of the ocean, though the amount of sunlight required does depend on the species of zoanthid. They require sunlight because of their symbiotic relationship with single-celled photosynthetic algae which produce most of the zoanthids needed nutrients.

Anatomy
The shape of both the single polyps and the colonies of zoanthids depend on the environment around the coral, but the basic shape of zoanthids looks like a colony of sea anemones. They have tube-shaped bodies topped with a flat, tentacle-ringed mouth.

Each polyp usually has more than one color, expanding outwards from the center of the polyp. If not it doesn't not, then the polyp probably has different shades of the same color.

Reproduction
Zoanthid coral can reproduce using both asexual and sexual means. The most common sort of asexual reproduction seems to be budding. The small polyps (buds) grow from the soft tissue know as the Coenenchyme, at the base of the mature polyp. The sexual reproduction of the zoanthid coral is just like most other corals; they are hermatypic and release sperm and eggs to create new colonies.

Ecology
Zoanthid coral, since it isn’t motile, feeds off nutrients that drift through the currents, called detritus. Detritus are microscopic bits of food, like algae and plankton. Other nutrients are produced by algae that live on the zoanthid coral called zooxanthellae, which produce these nutrients via photosynthesis. Zoanthids, like anemones, have very good protection against predators. The zoanthid coral uses a substance called palytoxin, which is one of the most toxic organic substances known to man, to defend itself. It is fatal if it is ingested or enters the blood stream, unless an antidote is administered immediately. Zoanthid coral are commonly found in aquariums along with other coral. They are well liked because of their vivid colors and are easy to propagate manually.

Related References

 * Zoanthid Wikipedia
 * What is Zoanthid Coral? by S. Mithra, wiseGEEK
 * Zoanthids Your Button Polyp Coral Resource by Blane Perun