Sea fans, also called gorgonians and sea whips, are nocturnal sea animals that look more like plants than animals. They are scientifically classified as belonging to the kingdom Animalia, the phylum Cnidaria, the class Anthozoa, the subclass Alcyonaria, and the order Gorgonacea. Sea fans are sessile, which means they cannot move around, and they are found exclusively in seawater environments. They live in oceans around the world. They are particularly suited to tropical and subtropical ocean water and are often found in shallow water near the state of Florida and places like Bermuda and the West Indies.
Sea fans consist of individual polyps that form colonies of the animals. These colonies normally stand vertically and appear flattened with branches, creating a fan-like look. However, they can sometimes appear bushy or look like whips. Sometimes they even appear encrusted. Colonies of sea fan polyps may grow to be many feet high and expand several feet across yet have only a few inches of thickness. Sea fans often appear in very bright colors, such as red, purple, and yellow.
The sea fan suborder Holaxonia is the one that forms flexible, fan-like appearances, which are referred to as gorgonin. The suborder Scleraxonia, on the other hand, has a skeletal foundation made of calcium-like structures that form dense groupings. Some species behave more like coral, encrusting like coral does. However, most sea fans do not attach themselves to hard matter. Usually, sea fans take up residence in mud or sand, and some need up to 8 inches (20.32 centimeters) of sand in which to anchor.
There are eight tentacles on each sea fan polyp. They are used to catch plankton and other tiny particles, which are then consumed. The process by which they eat is called filter feeding. Their successful feeding can be helped when they are positioned against the current in the water. This allows them to maximize their food supply.
Sea fans are most often found in shallow water. However, there have been some living several thousand feet below the water's surface. The way they look and how large they grow seems to depend on where they are located. For example, they have a more fan-like shape and are more flexible are typically found in shallower water that has stronger currents. On the other hand, those that are taller, thinner and far less flexible are typically found in deeper water that has a calmer current.
Interestingly, other types of sea fauna take up residence within sea fan colonies. These include brittle stars and hydrozoa. The pygmy seahorse is known to live among the branches of certain types of sea fans. However, this seahorse looks a lot like its sea fan host and is able to camouflage itself in its home.