Cnidarians

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Cnidarians

Cnidarians are invertebprices such as jellyfish and also corals. They belong to the phylum Cnidaria. All cnidarians are aquatic. Many of them live in the ocean. Cnidarians are a small more complicated than sponges. They have actually radial symmetry and also tconcerns. There are more than 10,000 cnidarianspecies. They are very varied, as displayed in Figure listed below.

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Cnidarian Diversity. Cnidarians present a lot of varicapacity.

You are watching: Cnidarians such as jellyfish have radial symmetry. how are the body parts of cnidarians arranged?


Structure and Function of Cnidarians

All cnidarians have somepoint in widespread. It’s a nematocyst, prefer the one shown in Figure below. A nematocyst is a lengthy, thin, coiled stinger. It has actually a barb that might inject poison. These tiny poikid "darts" are propelled out of special cells. They are used to strike prey or safeguard versus predators.

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Cnidarian Nematocyst. A cnidarian nematocyst is choose a poichild dart. It is ejected from a committed cell.

Tbelow are two standard body plans in cnidarians. They are called the polyp and also medusa. Both are shown in Figure below. The polyp has a tubular body and also is typically sessile. The medusa(plural, medusae) has actually a bell-shaped body and also is commonly motile. Some cnidarian species different between polyp and also medusa forms. Other species exist in simply one create or the various other.

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General Cnidarian Life Cycle. Cnidarians might recreate both asexually and also sexually.


Ecology of Cnidarians

Cnidarians can be found in almost all sea habitats. They may live in water that is shenable or deep, warm or cold. A few species live in freshwater. Some cnidarians live alone, while others live in colonies.

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Corals form large nests in shallow tropical water. They are confined to shpermit water because they have a mutualistic connection via algae that live inside them. The algae require sunlight for photosynthesis, so they must be relatively close to the surconfront of the water. Corals exist only as polyps. They capture plankton with their tentacles. Many secrete a calcium carbonate exoskeleton. In time, this builds approximately end up being a coral reef (watch Figure below). Coral reefs carry out food and also sanctuary to many kind of ocean organisms. They also assist safeguard shorelines from erosion by soaking up some of the power of waves. Cdental reefs are at risk of damage now.