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Here are a few fun facts about jellyfish...
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The most poisonous jellyfish, and indeed probably the most venomous marine creature, is the sea wasp or box jellyfish(Chironex fleckeri Southcott) from Australia. An adult is said to have enough poison to be able to kill sixty people, and swimmers do die after being sting by it (at least seventy people killed in the last 100 years). Death comes quickly (four minutes) from the toxin that acts on the heart. Apparently sea wasps can’t sting through tights – so, girls, keep your stockings on if you are paddling in box jellyfish land!
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Some jellyfish contain algae (microscopic plants) which photosynthesise and produce carbohydrates which the jellyfish can absorb. The algae, in return, get a safe and stable microhabitat (a kind of jelly greenhouse!) in which to live. This relationship between organisms where both partners benefit is called symbiosis (literally “living together”). One example is the upside-down jellyfish (Cassiopeia xamachana Bigelow) which contains a population of the microscopic alga Symbiodinium microadriaticum Freudenthal within its tissues. The algae release nutrients which the jellyfish absorbs. If the algae die, the jellyfish may waste away, consuming its own body.
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Jellyfish are primitive: they have no true eyes, heart, bones or other solid organs. They don’t have a brain but just a network of nerves that enable them to react to their environment, sensing “light”, “dark”, “up”, “down”, etc. We know that jellyfish have been on earth for at least 650 million years.
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Most jellyfish are marine and they are found in all the world’s oceans. A few live in lentic (still) fresh water such as inland lakes.
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Jellyfish swim by jet propulsion: their bodies pulse rhythmically to push them forward. They can also travel thousands of kilometres on sea currents or blown by the wind. Sometimes thousands or even millions are washed up on beaches.
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The largest jellyfish can attain a diameter of almost 2.5 metres. The species with the longest tentacles is the lion’s mane (Cyanea capillata (Linnaeus)), made famous by Sir Arthur Conan Doyle’s Sherlock Holmes story. It is to be found in colder seas, including those around Britain, and in arctic waters. Its tentacles can be 30 metres long.
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A jellyfish uses its sting to kill or stun prey. The stinging cells contain tiny capsules or nematocysts which can fire a minute barbed dart to deliver their poison. If a person is stung, don’t rub the sting and provoke more nematocysts to fire! Vinegar poured on liberally to flood the affected area immediately is should help to inhibit the firing of the nematocysts. Advice often given is to follow this by gently rubbing the area with fresh juicy papaya (pawpaw – Carica indica) or a proprietary meat tenderiser mixed with a little water which should aid in destroying the poison. (Meat tenderisers contain the enzyme papain from papaya that breaks down other proteins - the poison is a protein.) The immediate application of hot (not scalding!) water to flood the sting (or just sea water if there is nothing else) and a speedy trip to the doctor or hospital is probably as good advice as any. Like all stings, remember that a serious allergic reaction is a possibility. If you can identify or get a sample of the jellyfish (very carefully!) this makes the right treatment easier. In Australia, lifeguards may carry antivenin for the dangerous box jellyfish - and fast expert treatment is really, really important!
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And if you want to know more, click here for out full factsheet, where there is something a bit more complicated from fo those readers who want to know more about papain, which is the active ingredient in many meat tenderisers!
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