A class of arthropods, the body has a hard carapace, head and chest, head and thorax combined into the back of the abdomen. Head and chest front with the size of two pairs of antennae, the number of full range. Live in water and breathe using gills. Shrimp and crab are the most common crustaceans.
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No. 2
Crustaceans is a key link in the Arthropoda, its surface has a layer of chitin shell, called the carapace. Most crustaceans live in the sea, a few live in fresh water and land. Shrimp, crabs and other crustaceans have five pairs of legs, of which four pairs used for crawling and swimming, a pair of chelipeds used to resist the enemy and prey. Crustaceans including shrimp, crab, shrimp hook, comb and gills of shrimp foot subclass, ostracods subclass animals. The world's many different types of crustacean, about 26,000 kinds of many. Shrimp, crabs and other crustaceans, nutritious and delicious, with high economic value. Some fish, crustaceans or other economic animal feed. In crustaceans, there are also some species are harmful, such as barnacles and so on. In the sea mainly crustacean arthropods (30,000 kinds around the world), such as zooplankton constitute the main body of small copepods, the well-known delicious shrimp, crabs and exotic action nasty barnacles and so on. They are widely distributed, the size differences between small in only one meter so big, in the dissecting microscope to see, and the larger, such as the giant crab claws, two giant claws start to have more than 3 meters wide. Their way of life is varied, and some water to swim, and some bottom-crawling, and some attached to the rocks above the camp and other sessile, and some cave, and the camp parasitic life. Crab carapace developed abdominal degradation, commonly known as "umbilical", the male's sharp umbilical, umbilical female regiment. There are five pairs of legs, the first pair of legs is called chelation, is used to prey and enemies of Islam. Sideways crawl. There are many different crab, crab and so on. Meat is delicious. (Figure Title: trituberculatus)
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Feature
Because crustacean subphylum of animals so many states, so to find a common characteristic is not very simple. Crustacean subphylum and trachea animals (including sub-door six-legged insects, arthropods living on land) is relatively unique is that they have two pairs of antennae and gills to adapt to life in the water. However, these features are actually common features of the beginning of arthropods, six foot subphylum of animals these organs was changed. Another feature of the ancient crustacean subphylum forked animal foot, this foot in the fossil trilobites already have. Tracheal class was no such animal enough. Almost all of the crustacean subphylum of the animal has a special status of the larvae (nauplii). These larvae typically divided into three sections with a foot or tentacles, their nauplius eye is singular. Tentacles and foot in the door has a special sub-base of crustaceans, and pocket the excretory organ. In addition, all of the crustacean subphylum of stem cell division during the same characteristics. Like all other arthropods, crustaceans subphylum of the trunk by a number of sections. The first section is the head of the mouth anterior lobe, the last one is the rear tailgate. Through different ways of adaptation, this basic structure can form a very different way of special structure. In particular, the changes outside the limb can be very large (such as the evolution of mouthparts, sucker and genital organs are very different). Some sections can be integrated together to form a relatively large trunk (body segment). Overall crustacean subphylum animal's trunk can be divided into three parts: the head by the mouth before the leaves and may be formed after the fusion of six sections. Chest and abdomen of a different number of sections. The main distinction between the chest and abdomen from the outside reflected the combination of limb. Abdomen generally did not have limbs or only the evolution of the outer limbs. Sometimes the head and chest may also be fused together to form a head and chest.
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Reproduction and development
Amon crustaceans are also many kind of reproduction, the simplest are sperm and eggs into the water for external fertilization. But there are also external limb through the evolution of in vivo fertilization, and even some parasitic crustacean subphylum of animals inhabit the degradation of male genitalia in the female. Crustacean subphylum of the development process is similar. They generally experience multiple larval stage, the beginning of each larval stage larvae produced by budding the new section and the outer limbs. In addition to five animals outside the outline of all crustacean subphylum animals beginning larvae are typical nauplii. Some animals in the egg through the larval period. Since then the development of the different outline of the different animal larvae. Some crustacean subphylum After metamorphosis, some are not perverted into adults.
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Lifestyle
With a few exceptions almost all outside the crustacean subphylum animals live in water, marine and freshwater systems in all the ecosystems in both crustacean subphylum animals. A small number of species living on land, such as coconut crabs are hermit crabs, but during the development of these animals have to rely at least in the water. The only living almost entirely on land, crustaceans and other animals is enough to sub-door purpose animals (woodlice). Amon crustaceans living in the water in all the ecological environment. Many areas of the ocean plankton species composition, and other underwater life, Yanxi, coral reef or tidal. Ice in the Arctic and Antarctica, there are many crustaceans following Amon animals survive, they constitute the lowest level of local food chain. Near the ocean bottom Feiquan also crustacean subphylum animal life. Some animals feed on crustaceans Amon fish, other crustaceans subphylum vertebrate animals, or even the body.
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Evolution
甲壳动物 进化
Like other arthropods, like crustaceans subphylum of evolution is not very clear. The main reason is that they do not know the more difficult to save the fossil shells. The earliest fossils of crustacean subphylum appeared in the Cambrian, and today there are ostracods found in subclass and a subclass of soft animal fossils. The earliest crustacean subphylum animals living today may be similar to the paddle in the salt cave full outline, but they left no fossils. Gill appeared in the Devonian foot Gang, Man enough to subclass appear Silurian. In particular subclass Ostracoda shells of animals often appear in the sedimentary rocks, so it is important pointer fossils. Since their emergence from their zooplankton is an important part. Also often appear in the fossil of a barnacle.
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Classification
甲壳动物 分类
甲壳动物 分类
General crustacean subphylum animals and trachea animals (insects and centipedes) are regarded as sister groups. Some scholars believe that the insects and centipedes crustacean sub-door animals. The origin of this view is that the embryonic development of these animals the discussion. By molecular genetics and structural studies of sperm generally agree that the last part of today's doors five independent animals are crustaceans Asian Gang door. Crustacean subphylum within the classification and kinship is not very clear and great controversy. In recent years, new discoveries and research in this area so that turbulence is very large. Such as past head of the branch angle is now divided into more than one head, and so on. Most experts will crustacean subphylum is divided into five classes, but the key link to the gills full of controversy and crustaceans also great. Many scholars believe that the crustaceans is actually a collection of all the other four can not be assigned to the Gang of animals, is actually not a true outline. For other classifications also see the corresponding Wikipedia articles in English narrative.
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Ecological and economic significance
In marine crustaceans and freshwater ecosystems in the sub-door animals, especially small as zooplankton crustacean subphylum animals, played a crucial role. They eat the phytoplankton in the water, thus controlling the growth of these plants. Zooplankton in the amount of their share of the largest proportion. They are also other large water animals of the direct or indirect food. Some people directly eat crustacean subphylum animals (such as shrimp, crab and lobster). Crustacean subphylum also used to purify water, they have a filter dust, bacteria and single-cell organisms, combined with toxic substances and so on. Adsorbed on the hull of barnacles on the boat in the water can increase the resistance to economic losses.
