Crustaceans include shrimps, crabs, hooked shrimps, grass carp, branchiopods, ostracods and so on. There are many kinds of crustaceans in the world, about 26,000 species. Shrimp, crab and other crustaceans are rich in nutrition and delicious, which has high economic value. Some crustaceans are also food for economic animals such as fish. Among crustaceans, some species are harmful, such as barnacles.
Arthropods in the ocean are mainly crustaceans (there are more than 30,000 species in the world), such as small copepods, well-known delicious prawns, strange crabs and annoying barnacles. They are widely distributed and vary in size. Small as a grain of rice, it can only be seen clearly under the dissecting mirror. It's as big as a cancer, and its two giant claws are more than 3 meters wide. Their lifestyles are also varied, some swimming in the water, some crawling on the bottom of the sea, some clinging to rocks, some living in caves and some living in parasites.
The head and breastplate of crab are developed, and the abdomen is degenerated, commonly known as "umbilical cord", male pointed umbilical cord and female spherical umbilical cord. There are five feet. The first pair of feet are called claws, which are used to hunt and defend the enemy. Crawl sideways. There are many kinds, such as river crabs and swimming crabs. The meat tastes delicious. (Title: Portunus trituberculatus)
A segmented, crusty marine animal with five pairs of appendages on its head (the first two pairs are tentacles) that breathes through gills or skin. Crustaceans belong to the phylum Arthropoda, so they are named after their hard shells. There are more than 30,000 species of * * in the world, most of which are marine species, such as water fleas, water lice, barnacles, prawns and blue crabs.
A brief history of research In the 4th century BC, Aristotle recorded some crustaceans in his works. 1777, Pennant first used the term "crustacean" as a kind of arthropod. 1806, French P.-A. Latreille divided crustaceans into two subclasses: soft armor subclass and soft armor subclass. 1837, H. Milne-Edwards of France listed xiphophora and trilobite in the natural history of crustacea. In 1883, under Crustacea, Bojas established five subclasses: Branchiopoda, Oyster, Copepoda, tendril and soft armor. This is the embryonic form of modern crustacean classification, which has been used to this day. From 65438 to 0960, Physiology of Crustaceans, edited by T. wortmann, comprehensively summarized the research results before the 1960s. Since 1960s, the research on crustaceans has made rapid progress, especially in physiology, biochemistry and experimental ecology. With the discovery of many new life species and fossil species, the publication of a large number of papers on comparative morphology and life history, and the in-depth study on the origin, evolution and classification system of crustaceans, many scholars believe that the classification status of crustaceans should be raised to the level of superfamily, subfamily or phylum. T. E. Bowman and L. G. abel comprehensively summarized the research results in recent years in Modern Crustacean Classification (1982) and put forward a new classification scheme. Crustacean Biology, edited by D.E. Bliss, is a representative monograph at present, with 8 volumes published, as many as 1983.
Morphological crustaceans are long cylindrical, or shortened to bean or crab shape; Generally, the segmentation is obvious, but some segments often heal themselves, and parasitic types often lose segmentation and appendages.
The body consists of head, chest and abdomen. The head is generally small and consists of 6 sections; Except section 1; The other five segments each have 1 pair of appendages (2 pairs of antennae in front of the mouth, 1 pair of jaws behind the mouth, 2 pairs of jaws). The head-chest segment often heals, which is called the head-chest; There is often a carapace at the back edge of the head, called the head breastplate.
There is no obvious boundary between the chest and abdomen of lower crustaceans (such as branchiopoda), which is called trunk or trunk. Higher crustaceans (such as soft armor) basically have a fixed number of segments, including 8 segments in the chest and 7 segments in the abdomen.
The appendage consists of three parts: the handle is the original limb, and the end is bifurcated, which is divided into an inner limb and an outer limb. All animals except mollusks have no appendages in their bellies.
The appendages of the head and chest have different degrees of specialization. 1 and 2 pairs of appendages on the head are specialized into tentacles, which are more developed in the types of swimming life; The third pair and the fourth pair are specialized into the big jaw and the first small jaw, which have great morphological changes and are chewing organs. Generally, there are only protolimbs and inner limbs, and the latter becomes tentacles; The fifth pair of appendages is specialized as the second jaw, and the outer limbs of the advanced group (Decapoda) are developed, which are called jaw boats, and water can swing into the gill chamber by them.
The shape, quantity and function of trunk limbs (appendages behind the mouth) vary greatly among different groups. The basic structure is two branches, that is, the inner limb and the outer limb are separated from the original limb, such as the abdominal limb of shrimp. The trunk limbs of branchiopoda are leaflike feet, and there is no distinction between inner and outer limbs. There can be as few as 2 pairs in ostracods and as many as 60 pairs in branchiopods. Soft armor's trunk limbs have been divided into thoracic limbs (8 pairs) and abdominal limbs (6 pairs). The tail limbs and joints of swimming creatures often form a wide tail fan, which keeps balance when swimming, and the sudden buckling of the abdomen can make the body retreat quickly.
Taxonomically, crustaceans have always been regarded as a class of Arthropoda. In recent years, some studies have suggested that crustaceans should be upgraded from a class to a superclass, while others have suggested that crustaceans should be upgraded to a subphylum or phylum. There are different views. Due to the lack of data accumulation, there is no unified classification scheme at present. According to the classification system of Bowman and abel (1982), the main groups are listed below. In this system, crustaceans are divided into six classes, and the idea of E. Dabbour 1956 is adopted, and copepods, branchiopods, tendrils and shrimps are merged into Paeonopoda class, which is juxtaposed with cephalopods, branchiopods, paddlepoda, ostracods and molluscs into six classes. This scheme reflects the new progress of crustacean classification research. Together with the micro-animals discovered by G.A. bocks Schell and R.J. Lincoln in 1983, * * * belongs to 7 categories.
Cephalopoda is marine, with 4 genera and 9 species.
The appendages of branchiopoda trunk are leaflike. Most of them are freshwater species; There are few marine species, such as Artemia. * * * About 820 species.
There are only 1 species of pediatrics in the sea.
Tanturo Carida is a marine species and lives a parasitic life. There are four kinds.
Maxillopoda-like body types vary greatly, generally divided into head, chest, abdomen and many eyes. It is divided into four subclasses: ① Myxomys, marine, ***9 species. (2) Amphibia, all of which are marine products, and a few are brackish water species, such as barnacles. * * * About 1020 species. ③ The copepods of the subclass are mainly marine, accounting for the vast majority of marine zooplankton, such as squids. Some fresh water products. * * * About 8400 species. (4) Branchial subclass, mainly freshwater species, with a small number of marine species. * * * There are 150 species.
Ostracoda's body is not segmented, and there are two shells outside the body. Quite a few species live in the ocean, and a few species live in plankton, such as CYPRINIDAE, which are mostly benthic species. There are many kinds of fresh water. * * * About 5600 species.
Tall large crustaceans with or without head and breastplate; Trunk 15 ~ 16, with appendages except caudal segment; Paired compound eyes (several degenerations). It is divided into three subclasses: ① Phyllanthus, with double valves on the head and breastplate, shell-shaped, seven abdominal segments, and a tail fork on the tail segment. It's all seafood, such as Nebulia flounder. * * * About 10 species. Hoplocarida subclass has 5 pairs of jaw feet and 3 pairs of walking feet attached to the chest. All marines. * * * About 350 species. (3) True Soft Crustacea is the crustacean with the highest economic value, and there are many subclasses.
Biological characteristics Most reproductive crustaceans are hermaphroditic, but sedentary (such as tendrils), parasitic and a few free-living lower crustaceans are often hermaphroditic or short to adapt to the immobile lifestyle. Among the lower crustaceans (branchiopoda, Cladocera, Ostracoda), a few species can parthenogenesis, parthenogenesis and sexual reproduction alternately to adapt to the change of habitat.
Some amphipods (such as Squid) and a few shrimps (such as some species of Pan Da Luce) are hermaphroditic, that is, they first develop into males (testis matures first) and then turn into females (ovaries mature) in life history.
After the fertilized eggs of crustaceans develop and hatch, most of them have obvious larval metamorphosis. The basic structure is nauplii, and copepods, ostracods, tendrils, krill, prawns and some branchiopods all have nauplii. Arthropod larvae undergo different metamorphosis times before they develop into larval stages basically similar to adults.
Both growing and molting crustaceans have chitin exoskeletons in vitro (many species have thick calcareous shells), so they must molt (shell) to grow. After molting, the calcium accumulated in the stomach is used to enrich the new shell. Young crustaceans molt frequently and get old slowly.
Changes of sound, light and color Some crustaceans can make sounds, such as drum shrimp. When the fingers of their big paws are suddenly closed, they can make a loud sonic boom to defend against enemies or attract the opposite sex.
Some crustaceans can emit light. Some luminous bodies with complex structures, such as krill and cherry shrimp. Some only have simple light-emitting glands, such as marine fireflies (see marine luminous organisms).
Most crustaceans have certain color marks, which can change color with the living environment. This is because different pigment cells (mainly red, blue, yellow and black, but also green and brown) are scattered in the dermis of animals.
Ecological types Many crustaceans live in plankton, which is the dominant group of marine plankton. Among them, copepods, acropods, krill and decapods are common, such as shrimp, serge and lucifer. They are usually abundant and dense, and they are dominant in both surface and deep water bodies.
Most crustaceans are benthos. From the intertidal zone to the deep-sea trench of nearly 10,000 meters, different crustaceans live. There are a large number of crabs, hermits, isopods, amphipods and barnacles in the intertidal zone; There are many kinds of shrimps, crabs, shrimps, hooked shrimps, amphipods, Daphnia, ostracods and so on. Living in the subtidal zone and the shallow seabed of the continental shelf. At the bottom of deep sea and deep sea trench, the dominant species are Lian insects, Heteropods and some acropods. Some species live in caves under seabed sediments, such as Thalassina anomala, which lives in tropical mangrove swamps, and the cave depth can reach 1 m or more.
Many crustaceans live parasitically, such as copepods, such as fish lice (Ca-ligoida), jaw lice (Lernaeopodoidea) and root worms. And * * * habitat or * * * primitive living camp.
Many terrestrial species, such as coconut crabs, live on land, but they need to enter the ocean to breed and spend their larvae in the ocean.
Economic significance Many crustaceans are edible. The important thing is shrimp and crab. Although their output accounts for a small proportion in marine fisheries (see marine biological resources), they have high economic value because of their delicious meat and rich nutrition. Shrimp, in particular, has become the most popular high-quality seafood. At present, crustacean resources in remote seas and deep seas are also concerned by the world, especially Antarctic krill. Some people think that there are1~ 5 billion tons of reserves, and it is estimated that developing 50 ~ 70 million tons a year will not destroy resources.
Since the end of 1970s, shrimp culture in the warm sea area of the world has developed rapidly, and the shrimp culture output in many countries (including China) exceeds 654.38+00000 tons per year, which is expected to exceed the fishing output in the near future.
Many crustaceans are the natural food of marine fish. For example, marine planktonic crustaceans (copepods, mysids, some crustaceans and decapods) are the important food of pelagic fish. Benthic crustaceans are important food for pelagic fish and shrimp. Their number often affects the growth and development of economic fish, as well as the resources and output of fisheries.
Many crustaceans are harmful to human beings, such as Isopoda, Diptera, tendril barnacles and poisonous cooked crabs.