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jellyfish : the typically free-swimming, bell-shaped, usually sexually-reproducing solitary or colonial form of a cnidarian in which the whorls of tentacles lined with nematocysts arise and hang down from the margin of the nearly transparent, gelatinous bell — Webster
Jellyfish or sea jellies are the informal common names given to the medusa-phase of certain gelatinous members of the subphylum Medusozoa, a major part of the phylum Cnidaria. Jellyfish are mainly free-swimming marine animals with umbrella-shaped bells and trailing tentacles, although a few are not mobile, being anchored to the seabed by stalks. The bell can pulsate to provide propulsion and highly efficient locomotion. The tentacles are armed with stinging cells and may be used to capture prey and defend against predators. Jellyfish have a complex life cycle; the medusa is normally the sexual phase, the planula larva can disperse widely and is followed by a sedentary polyp phase.
Jellyfish are found all over the world, from surface waters to the deep sea. Scyphozoans (the “true jellyfish”) are exclusively marine, but some hydrozoans with a similar appearance live in freshwater. Large, often colorful, jellyfish are common in coastal zones worldwide. The medusae of most species are fast growing, mature within a few months and die soon after breeding, but the polyp stage, attached to the seabed, may be much more long-lived. Jellyfish have been in existence for at least 500 million years, and possibly 700 million years or more, making them the oldest multi-organ animal group.
Jellyfish are used in research, where the green fluorescent protein, used by some species to cause bioluminescence, has been adapted as a fluorescent marker for genes inserted into other cells or organisms. The stinging cells used by jellyfish to subdue their prey can also injure humans. Many thousands of swimmers are stung every year, with effects ranging from mild discomfort to serious injury or even death; small box jellyfish are responsible for many of these deaths. When conditions are favourable, jellyfish can form vast swarms. These can be responsible for damage to fishing gear by filling fishing nets, and sometimes clog the cooling systems of power and desalination plants which draw their water from the sea. — Wikipedia
Palau’s Jellyfish Lake reopens as thousands of jellyfish return (Maggie Hiufu Wong, CNN)
Ongeim’l Tketau Jellyfish Lake – Open to Visitors (Palau Gov)
Jellyfish Lake, Eil Malk island, Palau (Wikipedia)
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- Finding a rare fossilized comb jelly reveals new...on October 4, 2021 at 11:54 am
They look like jellyfish but they aren't. They seem inoffensive but are efficient predators—occasionally, they even eat fish. They are gelatinous and very delicate—and extremely rarely do they fossilize!
- Secrets of Fair Isle sea caves revealedon September 13, 2021 at 12:41 pm
Heriot-Watt divers have documented the hidden life of many of Fair Isle's remote sea caves for the first time.
- Sea of plastic: Med pollution under spotlight at...on September 8, 2021 at 7:36 am
Plastic packaging and discarded fishing nets bob in the tranquil waters of the Mediterranean, signs of the choking pollution that has stirred strong feelings at the world conservation congress in the French port city Marseille this week.
- Rare Cambrian fossils from Utah reveal unexpected...on August 20, 2021 at 8:43 pm
Ctenophores, also known as comb jellies, are a group of over 200 living species of invertebrate animals with a transparent gelatinous body superficially resembling that of a jellyfish. There is much interest in ctenophore evolution in recent years as their controversial phylogenetic position in the animal tree of life has prompted conflicting hypotheses. While some studies suggest they might represent the earliest branching animals, others suggest a more traditional position as close relatives […]
- Large numbers of giant jellyfish found off the UK...on August 17, 2021 at 12:24 pm
The UK has seen some exciting marine visitors recently, such as walruses, humpback whales and bluefin tuna, but a current group of arrivals has been much more of a cause of concern. Large numbers of huge stinging jellyfish have been appearing off the west coast of Scotland.