Cnidaria

Cnidaria is a phylum consisting of about 9,000 species of simple animals found exclusively in aquatic, mostly marine environment. From the point of etymology, the word Cnidaria comes from the Greek "cnidos" which means "stinging needles". Ability stinging cnidarians who is the origin of the name Cnidaria is typical mereka.Ciri knidosit, which is the specialized cells that they use mainly for capturing prey and defend themselves. Their bodies consist of mesoglea, a non-living materials like jelly, located between two layers of the epithelium is usually one cell thick. They have two basic body forms: swimming medusae and sessile polyps, both radially symmetrical with mouths surrounded by tentacles berknidosit. Both of these forms have one entrance hole that serves as the mouth or anus called an astronomer as well as the body cavity that is used for digesting food and breathing. Many cnidarians produce colonies meruapakan single organism composed of medusa-like zooids or polyps resemble or both. Cnidarians activities coordinated by a decentralized nerve net and simple receptors. Some Cubozoa and free-swimming Scyphozoa have a sense of balance and there have statokista ropalia, sensing a complex structure that can include the image-forming eyes with a simple lens and retina. All cnidarians reproduce sexually. Many cnidarians have complex life cycle with asexual polyp stage of development and sexual medusae, but some do not have a polyp or do not have a medusa.

In a long time, Cnidaria grouped with ctenophores in the phylum Coelenterata, but after more aware of their differences caused them to be placed in separate phyla. Cnidarians are classified into four main groups: Anthozoa which consists of sessile sea anemones, corals, and sea pens; and Scyphozoa (jellyfish), Cubozoa (box jellyfish) and Hydrozoa are three swimmers, diverse group that includes freshwater cnidarians and marine cnidarians as well, and has both sessile members such as Hydra and colonize swimmers such as jellyfish Portuguese warships. Staurozoa recently recognized as a separate class and not part of the Scyphozoa, and there is debate about whether Myxozoa and Polypodiozoa are cnidarians or closer to bilaterians (more complex animals).

Many cnidarians prey on organisms that range in size from plankton to animals several times larger size than their own, but many of them get the nutrition from endosymbiotic algae, and some are parasitic. Many cnidarians are preyed upon by other animals including starfish, fish and turtles. Coral reefs are rich in algae endosymbiotic polipnya, supporting some of the world's most productive ecosystems, and protect vegetation in tidal areas and on coastlines from strong currents and tides. While limited live coral in the warm and shallow sea water, other cnidarians live in the deep ocean, dai polar oceans and in fresh water.

Fossils of cnidarians have been found in rocks formed 580 million years ago, and other fossils show that corals are present shortly before 490 million years ago and became diversified a few million years later. Fossils of cnidarians that do not make a very rare mineral structure Scientists currently think that cnidarians, ctenophores and bilaterians loebih calcarea sponge closely related than the other sponge, and that anthozoa is "aunt" or "brother" evolutionary than other cnidarians, and more closely with bulateria. Recent analysis concluded that cnidarians, although considered more "primitive" than bilaterians, have a large range of genes.

Jellyfish stings killed several hundred people in the 20th century, and was a box jellyfish is particularly dangerous. On the other hand, some large jellyfish are considered as good food in eastern and southern Asia. Coral reefs have long been considered important to the economy as a fishing spot, building on the coast of protective currents and tides, and recently as a tourist center. However, they are vulnerable to overfishing, mining, building materials, pollution, and damage caused by tourism.

Typical

Animal phyla Cnidaria form komplels more than a sponge, almost as complex as ctenophores (comb jellies), and less complex than bilaterians, which include almost any other animal. However, cnidarians and ctenophores are more complex than sponges because they have: cells bound by inter-connecting cells and basement membrane-like carpet; muscle; nervous system, and some have a sensing organ. Cnidaria is different from other animals because it has a shot like a harpoon knidosit and used primarily for prey capture and berthing of some species.

Such as sponges and ctenophores, cnidarians have two main cell layers sandwiching a layer of jelly-like center called the mesoglea in cnidarians; more complex animals have three main cell layers and no intermediate layers like jelly. Therefore, cnidarians and ctenophores have traditionally referred to as diploblastik, along with a sponge. However, cnidarians and ctenophores have a type of muscle, the more complex animals, derived from the cells lining the middle. As a result some recent text books classify ctenophores as Triploblastik this, and it is estimated that cnidarians evolved from a common ancestor Triploblastik.