Tiny Umbrella Jellyfish





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Uploaded on Sep 27, 2010

Jellyfish (also known as jellies or sea jellies or Medusozoa) are free-swimming members of the phylum Cnidaria. Jellyfish have several different morphologies that represent several different cnidarian classes including the Scyphozoa (over 200 species), Staurozoa (about 50 species), Cubozoa (about 20 species), and Hydrozoa (about 1000--1500 species that make jellyfish and many more that do not).The jellyfish in these groups are also called, respectively, scyphomedusae, stauromedusae, cubomedusae, and hydromedusae. All jellyfish are embodied in the Medusozoa subphylum. Medusa is another word for jellyfish, and as such is used to refer specifically to the adult stage of the life cycle.

Jellyfish are found in every ocean, from the surface to the deep sea. Some hydrozoan jellyfish, or hydromedusae, are also found in fresh water; freshwater species are less than an inch (25 mm) in diameter, are colorless and do not sting. Many of the best-known jellyfish, such as Aurelia, are scyphomedusae. These are the large, often colorful, jellyfish that are common in coastal zones worldwide.

In its broadest sense, the term jellyfish also generally refers to members of the phylum Ctenophora. Although not closely related to cnidarian jellyfish, ctenophores are also free-swimming planktonic carnivores, are generally transparent or translucent, and exist in shallow to deep portions of all the world's oceans.
Since jellyfish are not actually fish, the word jellyfish is considered a misnomer, and American public aquariums have popularized use of the terms jellies or sea jellies instead. Others find jellyfish, which has been in common usage for more than a century,to be equally useful and picturesque, and prefer it over jellies. The word jellyfish is used to denote several different kinds of cnidarians, all of which have a basic body structure that resembles an umbrella, including scyphozoans, staurozoans (stalked jellyfish), hydrozoans, and cubozoans (box jellyfish). Some textbooks and websites refer to scyphozoans as "true jellyfish"

In its broadest usage, some scientists occasionally include members of the phylum Ctenophora (comb jellies) when they are referring to jellyfish.[10] Other scientists prefer to use the more all-encompassing term "gelatinous zooplankton", when referring to these, together with other soft-bodied animals in the water column.[11]

A group of jellyfish is sometimes called a bloom or a swarm.[12] "Bloom" is usually used for a large group of jellyfish that gather in a small area, but may also have a time component, referring to seasonal increases, or numbers beyond what was expected.[13] Jellyfish are "bloomy" by nature of their life cycles, being produced by their benthic polyps usually in the spring when sunshine and plankton increase, so they appear rather suddenly and often in large numbers, even when an ecosystem is in balance.[14] Using "swarm" implies some kind of active ability to stay together, which a few species like Aurelia, the moon jelly, demonstrate.[15]

Most jellyfish have a second part of their life cycle, which is called the polyp phase. When single polyps, arising from a single fertilized egg, develop into a multiple-polyp cluster, connected to each other by strands of tissue called stolons, they are said to be "colonial." A few polyps never proliferate and are referred to as "solitary" species



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