Zoanthids look like tiny sea anemones. But while true sea anemones are solitary polyps, most zoanthids live in colonies like corals do. But zoanthids don’t produce a hard skeleton like the hard coral colonies. Instead, their tissues are leathery and composed partly of chitin (the same substance that insect exoskeletons are made of).
The typical polyp has a cylindrical body column, topped by a smooth, flat oral disk that is edged by short tentacles, usually in two rows close to one another.
Zoanthids may have three different living arrangements.
- Each zoanthid polyp may be solitary but located near one another. These polyps are large with thick, fleshy polyps on tall columns.
- The zoanthid polyps are joined to one another by stolons (tube-like structures that spread across the ground like a root or runner).
- The zoanthid polyps may be embedded in a common mat of tissue. The tissue may be strengthened by incorporating sand. The colony may form mats on the sand or encrust rocky areas.
The shape of the same zoanthid species may vary depending on where they are found. Those inhabiting areas with strong waves tend to be short and hug the surface. Others found in deeper, calmer waters are taller, with longer tentacles.
Most zoanthids feed on plankton, some also feed on finer particles but also harbour zooxanthellae (symbiotic algae) inside their bodies. These carry out photosynthesis and may contribute nutrients to the host polyp.
Palytoxin, the poison extracted from a zoanthid, is used to treat of hypertension, heart disease and other disorders. Zoanthids are also a popular addition to the marine aquarium.
Source: Wikipedia
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