Coral reefs also support the tourist industry and a strong fishing industry. Organisms found on coral reefs have provided key ingredients for innumerable medical compounds that treat everything from asthma and cancer to HIV and still show potential for future pharmaceutical discoveries.
There are many subclasses and orders with varying characteristics under the class Anthozoa, including:. Order Scleractinia, Stony Corals : Stony or reef-building corals form a skeleton made of calcium carbonate under the polyps to create the hard structure that most people recognize as coral.
These corals are responsible for forming the base structure of coral reefs. As older polyps die off, new polyps continue to build calcifications on the old skeletons, allowing for the huge scale of reefs in the Caribbean and the Great Barrier Reef.
Not all stony corals are reef-building, though, as some are not able to produce enough calcium carbonate to facilitate reef formation. Subclass Octocorallia, Octocorals : Despite sharing a similar appearance with stony corals, soft corals, sea pens, gorgonians and sea fans do not build the hard, calcium-carbonate skeleton of stony corals.
Instead, these corals may create some internal structural supports that allow them to grow vertically but still sway with ocean currents. Soft corals are always colonial and grow with eight-fold symmetry, which means their tentacles come in groups of eight — hence the name Ocotocoral. Octocorals include the orders Alcyonacea and Helioporace.
Order Corallimorpharia, Anemone Corals or Mushroom Corals : Members of this order are sometimes called anemone corals or mushroom corals because they resemble anemones more closely than other types of corals due to their large, flat, disc-like shape and short tentacles.
They grow like wheel spokes, radiating from a center and forming concentric circles. The diameter of the circle increases as they grow. This order is extremely popular in home aquariums. Order Zoantharia, Zoanthids : Zoanthids have long, prominent tentacles arranged in two rows.
Unlike stony and soft corals, Zoanthids incorporate sand and other substrate into their colonies for structure. They may live as individual polyps or in colonial groups. Order Actiniaria, Anemones: Larger anemones tend to be solitary while smaller species may use asexual reproduction to propagate and live in large concentrations when there is suitable habitat.
Anemones come in a wide range of colors, some owing their coloration to the zooxanthellae, microscopic algae, they host. Anemones have a disc-shaped bottom they use to attach themselves to rocks, in crevices and on other suitable surfaces, including the shells of other marine invertebrates. Subclass Ceriantharia, Tube-dwelling Anemones: This subclass looks similar to sea anemones, but tube-dwelling anemones are known for being solitary and living buried in soft sediments.
They live inside tubes made of secreted mucus and organelles, and can recede into these tubes for protection. Ceriantharia includes the orders Spirularia and Penicillaria. Anthozoans are found from intertidal zones to deep ocean trenches, in both warm and cold waters. Reef-building corals are only found in shallow tropical and subtropical waters.
Anthozoa are found in the largest numbers in warm, tropical waters in coral reef habitats. Some corals receive their nutrition from mutualistic zooxanthellae that require sunlight for photosynthesis, the by-products of which are sugars consumed by the hosting coral.
Depending on their size, corals may catch prey varying in size from microscopic zooplankton to small fish. At the Smithsonian's National Zoo, anemones and corals are housed under special lighting fixtures and receive a mixture of minced clams, fish and shrimp. Corals can reproduce sexually and asexually. Asexual reproduction happens in the form of budding that occurs when a parent polyp produced by sexual reproduction divides, creating a colony of genetically identical but individual animals.
Corals also fragment during storms and these pieces can regrow into new colonies. A colony can grow to hundreds of thousands of individual polyps. Corals reach sexual maturity at different ages, varying by species and colony size. Some can mature and reproduce successfully in as little as four years, while others can take decades to reproduce.
Their bodies are composed of an adhesive pedal disc, or foot, a cylindrical body, and an array of tentacles surrounding a central mouth. The tentacles are triggered by the slightest touch, firing a harpoon-like filament into their victim and injecting a paralyzing neurotoxin. The helpless prey is then guided into the mouth by the tentacles. They run the full spectrum of colors and can be as small as half an inch or as large as 6 feet across.
Some anemones, like their coral cousins, establish symbiotic relationships with green algae. In exchange for providing the algae safe harbor and exposure to sunlight, the anemone receives oxygen and sugar, the bi-products of the algae's photosynthesis. They form another, more famous symbiotic alliance with clownfish , which are protected by a mucus layer that makes them immune to the anemone's sting. All rights reserved. Common Name: Sea Anemones. Scientific Name: Actiniaria.
Type: Invertebrates. Diet: Carnivore. Size: Diameter: 0. Size relative to a teacup:. This photo was submitted to Your Shot, our photo community on Instagram. Most jellies range from 2 to 40 cm in length but the largest scyphozoan species, Cyanea capillata , can reach a size of two meters in diameter. Scyphozoans display a characteristic bell-like morphology Figure 2.
Figure 2. A jelly is shown a photographed and b in a diagram illustrating its morphology. In the sea jelly, a mouth opening is present on the underside of the animal, surrounded by hollow tentacles bearing nematocysts. Scyphozoans live most of their life cycle as free-swimming, solitary carnivores. The mouth leads to the gastrovascular cavity, which may be sectioned into four interconnected sacs, called diverticuli.
In some species, the digestive system may branch further into radial canals. Like the septa in anthozoans, the branched gastrovascular cells serve two functions: to increase the surface area for nutrient absorption and diffusion, and to support the body of the animal. In scyphozoans, nerve cells are organized in a nerve net that extends over the entire body, with a nerve ring around the edge of the bell.
Clusters of sensory organs called rhopalia may be present in pockets in the edge of the bell. Jellies have a ring of muscles lining the dome of the body, which provides the contractile force required to swim through water, as well as to draw in food from the water as they swim.
Scyphozoans have separate sexes. The gonads are formed from the gastrodermis and gametes are expelled through the mouth. Planula larvae are formed by external fertilization; they settle on a substratum in a polypoid form. These polyps may bud to form additional polyps or begin immediately to produce medusa buds. In a few species, the planula larva may develop directly into the medusa. The life cycle Figure 3 of most scyphozoans includes both sexual medusoid and asexual polypoid body forms.
Figure 3. Scyphozoan life cycle. The lifecycle of most jellyfish includes two stages: the medusa stage and the polyp stage. The polyp reproduces asexually by budding, and the medusa reproduces sexually. However, cubozoans display overall morphological and anatomical characteristics that are similar to those of the scyphozoans. A prominent difference between the two classes is the arrangement of tentacles. The cubozoans contain muscular pads called pedalia at the corners of the square bell canopy, with one or more tentacles attached to each pedalium.
In some cases, the digestive system may extend into the pedalia. Nematocysts may be arranged in a spiral configuration along the tentacles; this arrangement helps to effectively subdue and capture prey. Cubozoans include the most venomous of all the cnidarians Figure 4.
These animals are unusual in having image-forming eyes, including a cornea, lens, and retina. Because these structures are made from a number of interactive tissues, they can be called true organs. Eyes are located in four clusters between each pair of pedalia.
Each cluster consists of four simple eye spots plus two image-forming eyes oriented in different directions.
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