Sea Anemone Lab Key

Body Parts:

The capitulum is an extension of the body wall above the collar.
The collar is a distinct fold a little below the tentacles.
The tentacles occupy the oral disc around the mouth.
The mouth opens into the actinopharynx, a throat-like passage which leads to the coelom.
The sphincter muscle runds around the margin of the oral disk and is used to contract the oral disk.
One mesentery (folded tissue) is shown on each side of the animal, and others radiate around the coelom.
The gametogenic tissue (sex organ) is embedded within the mesenteries between the musculature and the filaments.
The filaments compose a thickened rim running downwards from the actinopharynx, forming a border along the mesentery.
The acontia (nematocyst-studded filaments) protrude from the interior edges of the mesenteries.

Classification: The anemone is placed in the phylum Cnidaria, whose only freshwater member is the hydra.

Range and Habitat: Anemones are found in coastal areas all over the world, especially in warmer waters. They are found both in shallow and deeper water where they attach themselves to shells, rocks, timber, or other submerged substrata, by their basal disc.

Description: They range in size from less than a 1.25 cm (.5 in) to nearly 1.8 m (6 ft) in diameter. They are cylindrical in form with a crown of tentacles arranged in one or more circles around the mouth. The stalk ends with a smooth muscular basal disc on which the anemone can slide about very slowly.

Adaptations: The tentacles have stinging cells (nematocysts) which are used both for defense and capturing food. A nematocyst is a small capsule with a thread-like tube coiled inside. When a trigger bristle is disturbed, the coiled tube shoots out and imbeds in whatever triggered it. There is a minute amount of poison injected.

The nematocyst
before triggering
The nematocyst
after triggering

Diet: Anemomes are carnivorous, feeding on fish or almost any live animals of suitable size. Some species live on minute forms caught by the currents produced by the cilia on their tentacles. Sea anemones have a one-way gut. Food they capture with their tentacles goes into the mouth at the center of the animal. Later on, any undigested bits of food come out through the same hole.

Breeding and Maturation: Sexes are separate. The eggs or sperm are ejected through the mouth. The fertilized egg develops into a planula, which finally settles down somewhere and grows into a single anemone. Asexually they reproduce by pulling apart into 2 halves, or, in some species, small pieces of the pedal disc break off and regenerate into a small anemone.

Miscellaneous: Anemones form some interesting mutualistic relationships with other organisms. Many anemones house unicellular algae in their tissues from which they undoubtedly derive some nutrients. Some hermit crabs place anemones on the snail shells in which the crabs live, gaining some protection from the presence of the anemone, while the anemone dines on particles of food dropped by the crab. The clownfish form associations with large anemones. Somehow, these fish do not trigger discharge of the anemone's nematocysts, but if some other fish is so unfortunate as to brush the anemone's tentacles, it is likely to become a meal.

Biology Class