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Monday, February 8, 2010

Sea Jellyfish

Jellyfish are free swimming creatures belonging to the phylum of Cnidaria and while a few of them can be found in freshwater bodies or in rivers, a majority of jellyfish live in the sea. They are also known as jellies or sea jellies. There are several different species of jellyfish all grouped into different Cnidarian classes. Another word for jellyfish is medusa.

Sea jellyfish are made up of around ninety six percent water, three percent salt and one percent organic material. Although this may make these creatures seem fragile and simple, their body systems are made in such a way that they can survive quite well in the sea.

The bodies of sea jellyfish have three different layers of tissue. The outer layers is for protection, the middle is made up of a thick elastic-like material and the innermost layer makes up the gut of the jellyfish and is used for digesting food. This gut acts as the jellyfish's stomach, intestine and gullet. These sea creatures have no other organs and lack a heart, brain, kidneys or liver and also lack major body systems. However, they do have a 'nerve net', which consists of receptors that are sensitive to light, currents, odours and other changes in the environment, and acts as their 'brain'. It tells the jellyfish how to respond to these chances.

Jellyfish have a single opening for both the ingestion of food as well as the removal of waste products. Sea jellyfish feed on zooplankton such as larvae, larval fish, krill and gelatinous mammals. The umbrella-like part of the jellyfish is known as the bell, and this is used to push them through water. Some sea jellyfish have no propulsion and instead just float along with the currents and waves of the sea.

Another common feature of sea jellyfish is that they contain tentacles, and some have nematocysts on them. These nematocysts are small stingers that are usually triggered by touch. If something brushes against the tentacle of a jellyfish, it can get stung by these nematocysts or stinging cells. This results in the object being stunned and is how jellyfish feed. Once the object can no longer move, the jellyfish ingest it.

There are many different types of jellyfish, and while most, like the Umbrella Jellyfish, are completely harmless, others, such as the Portuguese Man of War can be fatal. If you are stung by a jellyfish you should get out of the water as soon as possible and remove the tentacles to avoid any more stinging. Meat tenderizer is used by many lifeguards as it breaks down the toxin that the tentacles pump into the body. Milder jellyfish stings can be treated with sea water or some vinegar to relieve the itching, burning or prickly sensations that one might encounter.

Most of the time sea jellyfish are completely harmless but often misunderstood. They rarely look for people to sting, and usually sting humans completely by accident, while brushing up against them after the currents have wafted them near the shores of beaches.

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