Characteristics: Sea anemones are a large group of soft bodied animals closely related to coral forming polyps and belonging to the same phylum as the jellyfish. Like all these creatures, their bodies have a simple structure, consisting of an inner and an outer layer of cells. The inner layer surrounds a central cavity, with one opening to the outside world for food and waste. The outer layer consists of a mass of fleshy tentacles radiating from around the mouth. Each tentacle is armed with special stinging cells used for both defense and attack.

Sea anemones cannot move since they are anchored to the seabed or to rocks or corals. A special disc on the base of each animal produces a cement that secures it even if it is exposed to waves. But sea anemones can move their tentacles. Those that inhabit tidal zones retract their tentacles completely when they are exposed at low tide.

Special Relationships: The sea anemone provides one of nature’s best examples of symbiosis – a relationship in which two types of organisms benefit from living closely with one another. The cloak anemone lives on the shell of the hermit crab. The crab gains protection from predators, which are driven off by the anemone’s stinging cells, while the anemone gets food scraps discarded by the crab. In tropical waters, certain species of fish live among sea anemones’ tentacles. The most famous is the clownfish, which has a covering of protective mucus that prevents it from being stung by the sea anemone’s tentacles. In this way the clownfish gains protection from predators.

Reproduction: Sea anemones reproduce in various ways. Some simply divide their bodies into two new anemones. Others split off sections of their basal discs, which then develop into new animals. In some species, each animal produces eggs and sperm; in others, the sexes are separate. The eggs and sperm are released into the water, with fertilization depending upon the different sex cells drifting into contact with one another. Then fertilized eggs develop into larvae that settle on the seabed and grow into young anemones.

Food and Feeding: Sea anemones are carnivorous (meat eating) and use their waving tentacles to catch prey. Smaller species draw organisms into their mouths by beating tiny hairs on the tentacles to create a current. Larger species prey on fish and crustaceans, using powerful stinging cells to stun or kill. A sea anemone has a muscular tube leading from its mouth into its body cavity. After prey passes through, digestive juices break down the food, which is then absorbed into the sea anemone’s tissue.

Naturewatch: The common beadlet anemone, a small red or green species found along the shore, is often seen when the tide is out, with its tentacles retracted. Rockpools on the west coast may also be the home of the snakelocks anemone, which has green tentacles, tipped with violet. The larger plumose anemone, with its pink or whitish tentacles, occurs in deep water.

Key Facts:
Sizes:
Length: From less than an inch to more than 3 feet in diameter

Breeding:
Asexual: Divides or buds
Sexual: Releases eggs and sperm into the water, followed by a free swimming larval stage. Also fertilizes internally

Lifestyle:
Habit: Solitary. Attaches to the seabed or other surfaces
Diet: Varies from plankton to fish, according to size of species

Related Species: The sea anemones are grouped with the corals in the class Anthozoa. This class contains some 6,500 species.

Distribution: Sea anemones occur in most of the world’s seas at varying depths, but they are most numerous in tropical waters.

Conservation: Some tropical species may be affected by pollution and by the exploitation of reefs.

Features of the Sea Anemone:
Basal disc: Located at the sea anemone’s base, it produces a cement like substance that anchors it to a rock or coral.
Tentacles: Covered with stinging cells, they stun the anemone’s prey, then draw it into its mouth.
Mouth: Contains microscopic hairs that beat constantly to circulate water around the body.
Mucus: Sticky; secreted by the tentacles to hold its prey.

Did You Know: 
Sea anemones get their name from the colorful wildflowers, anemones.
Some of the largest sea anemones, found near Australia, grow to over three feet in diameter.
Some species of sea anemone burrow into holes in mud and sand.
A sea anemone has no brain. Instead, its nerve cells form a network that connects its sense organs and its muscles.
The dahlia anemone camouflages itself with bits of shell and sand.
 

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