October 01, ; Accepted: October 06, ; Published:
Octocorallia includes blue coral and soft corals and species of Octocorallia have polyps with an 8-fold symmetry, each polyp having eight tentacles and eight mesenteries. Fire corals are not true corals, being in the order Anthomedusa sometimes known as Anthoathecata of the class Hydrozoa.
The body unit of the animal is a polyp. Most corals are colonial, the initial polyp budding to produce another and the colony gradually developing from this small start. In stony corals, also known as hard corals, the polyps produce a skeleton composed of calcium carbonate to strengthen and protect the organism.
This is deposited by the polyps and by the coenosarcthe living tissue that connects them. The polyps sit in cup-shaped depressions in the skeleton known as corallites. Colonies of stony coral are very variable in appearance; a single species may adopt an encrusting, plate-like, bushy, columnar or massive solid structure, the various forms often being linked to different types of habitat, with variations in light level and water movement being significant.
Soft corals are very variable in form and most are colonial. A few soft corals are stolonatebut the polyps of most are connected by sheets of coenosarc. In some species this is thick and the polyps are deeply embedded.
Some soft corals are encrusting or form lobes. Others are tree-like or whip-like and have a central axial skeleton embedded in the tissue matrix.
In both stony and soft corals, the polyps can be retracted, with stony corals relying on their hard skeleton and cnidocytes for defence against predators, and soft corals generally relying on chemical defences in the form of toxic substances present in the tissues known as terpenoids.
The mouth of each polyp is surrounded by a ring of tentacles. In stony corals these are cylindrical and taper to a point, but in soft corals they are pinnate with side branches known as pinnules.
In some tropical species these are reduced to mere stubs and in some they are fused to give a paddle-like appearance. Shallow water species of both stony and soft corals can be zooxanthellatethe corals supplementing their plankton diet with the products of photosynthesis produced by these symbionts.
These cells carry venom which they rapidly release in response to contact with another organism. A dormant nematocyst discharges in response to nearby prey touching the trigger cnidocil.
A flap operculum opens and its stinging apparatus fires the barb into the prey. The venom is injected through the hollow filament to immobilise the prey; the tentacles then manoeuvre the prey to the mouth.
Once the prey is digested, the stomach reopens, allowing the elimination of waste products and the beginning of the next hunting cycle. They can scavenge drifting organic molecules and dissolved organic molecules.
By using this technique, zooxanthellae are able to supply corals with the products of photosynthesis, including glucose, glycerol, and amino acids, which the corals can use for energy. Due to the strain the algae can put on the polyp, stress on the coral often drives them to eject the algae.
If the stressful conditions persist, the polyp eventually dies. Reproduction also allows coral to settle in new areas. Reproduction is coordinated by chemical communication. Sexual[ edit ] Life cycles of broadcasters and brooders Corals predominantly reproduce sexually.
The gametes fuse during fertilization to form a microscopic larva called a planulatypically pink and elliptical in shape. A typical coral colony forms several thousand larvae per year to overcome the odds against formation of a new colony.
Synchronous spawning is very typical on the coral reef, and often, even when multiple species are present, all corals spawn on the same night. This synchrony is essential so male and female gametes can meet.
Corals rely on environmental cues, varying from species to species, to determine the proper time to release gametes into the water. The cues involve temperature change, lunar cycleday lengthand possibly chemical signalling.
Brooders[ edit ] Brooding species are most often ahermatypic not reef-building in areas of high current or wave action. Brooders release only sperm, which is negatively buoyant, sinking on to the waiting egg carriers who harbor unfertilized eggs for weeks.The Importance of Biomes - The importance of Biomes Biomes are the living spaces of life.
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Algae are a huge community of organisms with forms that are unicellular (i.e. that consist of only one cell) and forms that are multicellular (i.e. that consists of multiple cells) . Facts, figures and findings from application of Toxkit microbiotests are reported in a large number of publications, reports and presentations at scientific symposia and workshops.
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