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Class Anthozoa includes Cnidaria that have no jellyfish stage. This is the largest class of cnidarians, containing over 6,000 species. A gullet extends for a short distance into the gastrovascular cavity, and septa are present, which increase the surface for digestion and absorption. Anthozoa are flower animals, including a great many beautiful and colorful organisms, e.g., the sea anemone, sea pansy, sea fan, and coral. Anthozoans are colonial or solitary organisms.
Subclass Alcyonaria
Subclass Alcyonaria includes almost universally colonial organisms in which each of the polyps, or hydroid members, has eight feathery tentacles. Most of them produce a skeleton, and many make some contributions to coral reefs. While some are found in temperate seas, they are especially common in subtropical to tropical regions. The organ pipe coral (Tubipora), a soft coral (Alcyonium), the Indo-Pacific blue coral (Heliopora), and the sea pens, which have a stalk extending into the bottom mud or sand, are some typical alcyonarian corals. Horny coralare perhaps the best known. These form branching, upright colonies and have a skeleton that is partly composed of a horny material called gorgonin. These are the sea whips and sea fans so characteristic of shallow tropical waters.
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