This is your best opportunity to keep learning about all the marine species such as the sea anemones, which are members of the Actiniaria’s invertebrate order (class Anthozoa, phylum Cnidaria) and are characterized by being sedentary sea animals that resemble flowers.
They are found from the tidal zone of all oceans to depths of more than 10,000 meters (about 33,000 feet). Some of them live in brackish water. They are larger, more numerous, and more colorful in warmer seas and shallow tropical reefs, but there are some in colder waters, in deep waters and even intertidal waters. The colorful Tealia are found in temperate regions. These wonderful creatures are sessile polyps, which means that they are attached to the ground, (on sand or rocks), using what is called a «basal disc» to maintain a sticky point of support.
Table Of Content
Sea Anemones’ Main Characteristics
There are approximately 1,000 species of sea anemones, whose size varies from a few millimeters in diameter and length to approximately 1.5 meters in diameter. The largest sea anemones, also the largest cnidarians, belong to the genus Stichodactyla.
These creatures present a huge variety in form and habit. Their cylindrical body can be thick and short or long and thin. The oral disc, which contains the mou
th, is surrounded by petal-shaped tentacles, which are often present in multiples of six. Sea anemones are commonly yellow, green or blue and are usually joined by a pedal or base disc, to a hard surface, such as a rock, pier wood, a shell or the back of a crab. They almost never move, some crawl occasionally, or move around in a kind of cartwheel.
The members of certain genres (for example, Edwardsia, Halcampa, Peachia) have no pedal disc, but sink deep into the sand or mud, exposing only the mouth and the tentacles. Members of the genus Minyas float near the surface of the ocean, with their mouths hanging down.
Sea anemones lack of solid skeleton, but they can secrete a corneal cover. Some species have adhesive secretory structures and are covered with grains of sand, pieces of shell or other foreign objects.
They have stabbling microscopic structures in the tentacles, (nematocysts) which they use to capture and paralyze prey such as fish and other marine animals. Some species only eat microorganisms. At the same time the anemones are common prey of the marine slugs, certain starfish, eels, flounders and the codfish.
How the Sea Anemones Reproduce?
In most species the sexes are separated. Sperm and eggs are usually discharged into the water, where fertilization occurs. Sometimes, the sperm enter the female´s gastrovascular cavity , in which the eggs are fertilized. Fertilized eggs develop, becoming ciliated larvae which disperse to new areas before becoming adults. The reproduction also takes place asexually by fission in some occasions, that is to say, the animal divides longitudinally in two equal individuals. In some species (for example, Metridium), the pedal disk is broken into fragments which become in new specimens.
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Main Habits of the Sea Anemones.
Sea anemones often live in close association with other organisms. The hermit crab usually carries a single anemone of the Calliactis genus on the conch’s shell that it uses as «home». When the hermit crab grows too much for its shell, it moves to a new shell, transplanting the anemone with it. Fish of the Premnas and Amphiprion genera often live among the venomous tentacles of an anemone, such as those of the Stichodactyla, Radianthus or Discosoma species. Such fish, however, can be minced and eaten by other anemones, even of the same species.
The Sea Anemones’ Poison
The cnidocytes located in the sea anemones’ tentacles, contain urticating nematocysts. Each nematocyst contains a small venom vesicle filled with actinotoxins, an internal filament and an external sensorial hair. A touch of these hairs mechanically causes a cellular explosion, which launches a structure similar to a harpoon that adheres to the organism that triggered it, and injects a dose of poison into the flesh of the aggressor or prey. This phenomenon is harmless to humans to which only produces a sticky sensation.
In the case of their prey, it is a completely different story. Small marine anemones eat small planktonic creatures; while the largest eat fish and crustaceans. The toxins paralyze their food so they can’t escape. Next, they use the tentacles to maneuver the prey in their mouth. Once inside, digestive enzymes are released and everything that can´t be eaten is simply spit in the same way it entered. Many sea anemones can retract their tentacles if necessary, thus resembling a piece of gelatin.
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