Beautiful Pictures Of Jellyfish
Jellyfish are any planktonic marine member of a group of invertebrate animals composed of about 200 described species of the class Scyphozoa (phylum Cnidaria) or of the class Cubozoa, which was formerly considered an order of Scyphozoa. The term, jellyfish, is also often used in referring to certain other cnidarians that have a medusoid (saucer- or bell-shaped) body form, such as hydromedusae, the siphonophores (including even the Portuguese-man-of-war which technically is not a jellyfish but a pelagic colonial hydroid or hydrozoan), as well as unrelated forms such as salps and comb jellies.
Most feed on small animals that they catch in their tentacles' stinging cells (nematocysts). Others simply filter feed, extracting minute animals and plants (i. e., plankton and nekton, loosened benthos) from the ocean water as they drift. Like all cnidarians, their bodies are made up of two cellular layers, the ectoderm and the endoderm. Between these dermal layers lies the mesoglea, a layer of connective tissue composed of a gelatinous substance, the jelly. In jellyfish the mesoglea is much enlarged to form the buoyant, transparent jelly. They float in the sea - only a few jellyfish live in fresh water. Most live for only a few weeks, although some are known to survive a year or longer. A jellyfish is 98% water.
There are many types of jellyfish. The smallest jellyfish are just a few inches across. The largest jellyfish is the lion's mane (Cyanea capillata), whose body can be over 3 feet (1 m) across, with much longer tentacles. Some jellyfish glow in the dark (this is called phosphorescence). Some of the deadliest jellies include the box jelly (Genus Carybdea) and the tiny, two-cm-across Irukandji jelly (Carukia barnesi); the venomous sting of these jellyfish can kill a person. Seventy of the 200 species of jellyfish are known to sting - causing a range of reactions in humans: from mild skin irritation to death. The sting of the sea wasp, Chironex fleckeri ((Genus Carybdea), is so toxic that it can cause death. Some even call this creature the "deadliest animal on earth."
Free-swimming Scyphozoan medusae jellyfish occur in all oceans and include the commonly familiar disk shaped animals that are often found floating along the shoreline. The bodies of most range in diameter from about 1 to 16 inches (2 to 40 centimeters); however, some species are considerably larger with diameters of up to 6 1/2 feet (2 meters). The bulk of the Scyphozoan medusae jellyfish consists of almost ninety-nine percent water as a result of the composition of the jelly that forms the bulk in nearly all species.
Jellyfish are very common in all water bodies. Do not go into areas where they are sighted, or if dead ones are seen on the beach. Their primary injury mechanism is their tentacles' stinging cells (nematocysts). Symptoms include stinging, burning sensation, vivid redness in the affected areas, swelling of lymph nodes. There may be severe reaction: difficulty with breathing and even cardiac arrest. Visible manifestations include long red welt lines.