Invertebrates, a, body soft, no links, bilaterally symmetrical, is enough meat, the majority of the hard shell with calcium, a wide range of life, both in water and on land, such as mussels Lo ﹑ ﹑ ﹑ squid, snails, etc. .
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ruǎn tǐ dòng wù
Zoology terms of an invertebrate, soft body, no link is enough meat, most with hard shell. Such as mussels, snails, snails, squid, etc.
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No. 3
molluscs [Overview] Molluscs (cephalopod) populations, including squid, octopus, nautilus, and extinct ammonites and arrows stone. It has long tentacles around the mouth to grab prey, moves forward to take advantage of the siphon jet action. Molluscs (mollusca) is a second door to the animal kingdom. Molluscs are three germ layers, bilaterally symmetrical, with a true animal body cavity. True body cavity is formed by a split molluscs chamber method, a body cavity is formed in the mesoderm. Soft body, usually symmetrical, certain species due to the reverse, inflection, and showed a variety of strange forms. Usually have the shell, no body section, there is enough meat or wrist, there are enough degradation. The outer layer of skin from the back of the jacket folds into a so-called, will surround the body and secrete a protective calcareous shelly. Born gill breathing and body cavity between coats. Land and water are distributed throughout. Including dual nerve Gang (such as chitons), gastropods (such as abalone, snails); dig foot outline (eg angle shellfish), Lamellibranchia (such as cockles, oysters), cephalopods (such as squid, nautilus), etc. . One animal body cavity door. Haraguchi are animals, true body cavity classes end cell dry. Since gastropods become secondary to reverse visceral block of left-right asymmetry, and various other classes of system are symmetrical. Body from head (Lamellibranchia no), foot and visceral blocks. Visceral epidermal extension to form the mantle block, wrapped in the main part of the body. It is the space between the internal organs of the mantle cavity block, there gills, digestive and excretory organs end opening here. No body section structure. In vivo clearance for irregular blood chamber. True body cavity due to narrowed mesenchymal developed form only pericardial cavity, the cavity and the renal tubular lumen gonads (reproductive cavity). Head with eyes and mouth and feeling. As foot movement organs, muscles smooth muscle, which related to its slow movement. Ink twill muscle wall. Mantle outward secretion shells. Different classes in different shells in the number and shape. Digestive tract long, usually toothed tongue and salivary glands in the mouth. Midgut gland opening in the stomach. The gills are generally 1 pair, corresponding to 2 appendage a heart ventricle. But in cephalopods with two pairs of species in the gills there are four atrial appendage. Gastropods because visceral block reverse, some only one of the gill (1 appendage a heart ventricle), and some species disappear and the wake is replaced coat gills. Terrestrial gastropod snails in the lung, part of its mantle has evolved into the lungs. To open vascular system, respiratory pigment hemocyanin mostly. Clams, snails and other flat volume compared with hemoglobin. Renal excretion is to pipe (Bao Yena's devices) based, but there's a Kaibo's species (bivalves). Nervous system as a particular type, in addition to a head on esophageal ganglia, also has side ganglia, ganglia and dirty foot ganglion each one right. Each pair of the same nerve ganglion by the cross ties and other head ganglion nerve ganglia linked by a vertical. Hermaphrodite or allogeneic. In the male, the ship maggots and abalone, etc., see the sexual conversion. Apart from cephalopods, underwent spiral cleavage by trochophora larval period and the face plate; But the cleavage of cephalopods is symmetrically direct development. Main Features Molluscs morphology large variation, but the basic structure is the same. Soft body with a hard shell, the body hidden in the shell, in order to be protected, because the crust would hinder activity, so their actions are quite slow. Unsegmented, can be divided into head, feet, viscera of three parts, extracorporeal membrane quilt, often secrete shells. Foot is shaped like an ax, with two shells, such as male. People speculated that the original mollusks appear Precambrian, living in shallow, oval body, the body length of not more than 1cm, symmetrical on both sides of the head at the front, with a pair of antennae, base of antennae eye. Ventral body flat, full of muscle mass, form suitable for crawling foot. The back of the body is covered with a coat of convex shell (shell), to protect the entire body. May initially be formed from only the shell of keratin called shell elements (conchiolin), after the deposition of calcium carbonate on the shell element, increasing its hardness. The following is a shell structure of the membrane bilayer of the cell to the ventral body wall extending from the formation, said mantle (mantle) (or pallium), it has a strong secretory capacity, i.e. the shell is formed by the mantle. Under the mantle covered with visceral sac. The rear end of the body, the top of the foot there between a cavity and the visceral sac, is the outer chamber (mantle cavity), which communicates with the outside. There are many on the mantle cavity rows of gill respiration, as well as renal, anal, genital pore openings. Raw molluscan gill structure may be similar in extant gastropods gills, it is by a long gill extending axially alternating sides of the triangle composed of gill filaments, which called comb gill gill (ctenidium). Gill axis extending outward from the mantle or body wall, which contains blood vessels, muscles and nerves, the leading edge of the gill filaments (ie, ventral margin) with bone support chitin rods to increase the hardness of the gills. Gill coat both sides of the back cavity, respectively, intraperitoneal fixed position, and therefore the outer gill cavity into upper and lower chambers. Water from the lower chamber flows into the rear chamber jacket by gill surface and the ventricular outflow mantle cavity, gill leading edge and surface covered with cilia, causing water to flow in the mantle cavity of the swinging cilia. Gill shaft with two vessels, into the back of gill blood vessels (afferentblood vessel), the ventral edge of the gill blood vessels (efferent blood vessel), the flow of blood from the blood vessels into the gill gill blood vessels, but also by the gill surface directly microvascular flows from the ventral edge of the back edge so that the flow direction opposite the flow direction of the gill surface, the gas can be more efficiently exchanged. Like many extant original mollusk species, like the gill surface covered with cilia not only its mantle and skin (including the skin of the foot) portion of the cloth have cilia, swing these cilia cause constant water flow through, in order to facilitate the exchange of gases and prey, the original skin respiration in molluscs is very important. Cilia movement of the foot joint and muscle contraction also constitute the body's movement. Raw mollusks may be herbivorous, feeding on algae growing shallow rocks. Have the same feeding mollusks existing structure. The port is located in front of the head, mouth after oral (buccal cavity), the rear end of a bag-shaped mouth radula sac (radulasac). The bottom of the radula sac membrane with a forward and backward activities to bring the distribution of the film take place in a row, neatly arranged chitin fine-tooth, tooth tip backward, film tapes and teeth constitutes radula (radula), radula at the bottom of the bag has a radula cartilage (odontophora), attached to the tongue and teeth cartilage extensor (protractor muscle) and muscle contraction (retractormuscle), by stretching muscles, cartilage, and can be extended extraoral film tape to scrape food, Since feeding wear thin front teeth missing aging, the film with the back-end can continue to secrete complement the new gear, which substitute daily rate is the number of rows of many mollusks. This radula of mollusks in most of the existing structure is there. On the back of the mouth opening with a pair of salivary glands, which can smooth radula secretions and food particles into the mouth sticking together to form a food rope, cord food into the stomach via the esophagus. Hemispherical front of the stomach, the side of the inner wall of the stomach with chitin plates, said 榡 stomach (gastric shield), the opposite side of the ridge and the formation of many small ditch, the ditch with cilia, called the screening area (sorting region ). The second half of the stomach into the cystic sac called crystal rods (style sac), because of which there is a gelatinous rod structure, called crystal rods (crystalline), the inner wall of the bag also has a crystal rod folds and cilia, also formed cilia ditch. After the food in the mouth sticky mucus forming foods cable is continuously into the stomach, relying on gastric acid (ph value of the existing types of gastric juice is generally 5-6) to remove the sticky foods cable, making cable free of food particles, Meanwhile screened by ciliary action of the stomach area were screened for food, tiny food particles by the digestive gland of the upper end of the tube into the stomach digestive gland, the gland is the digestion of food, and the intracellular uptake sites; larger food particles in the stomach was performed extracellular digestion; unable to digest food through the stomach and into the intestine folds, then digestion by the intestinal part of the final form of fecal pellets in the gut. Anal opening in the mantle cavity back end, formed fecal pellets of reducing pollution to the mantle cavity of fecal pellets excreted by the water. Raw molluscan body cavity located in the back of the body, which surrounds the heart and part of the intestine, so in fact represent the pericardial cavity and confining dirty. Cardiac ventricle and the rear end includes a pair of distal end of the atrial appendage from the ventricle through the branch arteries through the formation of small blood vessels, and finally into the tissue is formed in the gap between the sinusoid, and then pooled into a vein sinus, through the kidney, gill blood is flowing atrial and ventricular, this is an open loop. Blood contains deformed cells and respiratory pigment, mainly respiratory pigment hemocyanin (hemocyanin). Excretory organs as the kidneys, located on both sides of pericardial cavity, renal end communicates with the pericardial cavity called the renal mouth (nephrostome), end with the outside world, known outside the kidney hole (nephridiopore). Pericardial accepted by the heart and pericardial glands release of metabolites, with pericardial fluid from the mouth into the kidneys kidney, kidney has the ability to absorb a certain weight, it will be useful salts recycling, waste becomes useless into the urine, kidney hole through the outer jacket chamber and then excreted. Neural structures of the original mollusk is very simple around the esophagus to form a nerve ring, two pairs separated by a nerve ring nerve cord, a symmetrical foot ventral nerve cord (pedal cord), disposable foot muscle contraction; back of a symmetric splanchnic nerve cord (visceral cord), govern the movement of internal organs and jackets. According to the existing molluscs speculated may also include a sensory eye, a pair of balanced balloon (statocyst) inside the foot, and a pair osphradium (osphradia), which is located under the gill membranes, is a chemical receptors. Reproductive system includes a pair of gonads, located pericardial front in the back, dioecious, no reproductive ducts, sperm or eggs mature released into the pericardial cavity, as part of the gonad cavity is also a body cavity, so the germ cells by pericardial cavity, and then routed through the kidneys in vitro. Fertilization occurs in seawater, raw molluscan embryos may be very similar to the existing molluscs, also typical spiral cleavage, blastocyst formation hole oral, formed after gastrulation trochophora (trochophore). Trochophora was pear-shaped, with a typical cilia cilia before opening round (prototroch), in the upper part of the body around the mouth, when the first four collective cleavage are at the top, as well as the top beam. Trochophora not only in mollusks, also appears in the annelid. The original species development after only trochophora, most existing mollusks trochophora a very short period, and subsequently into veliger stage (veliger larva). Face plate appears full, shell, viscera and other structures when the larvae. Speculated that the original did not face plate mollusk larvae, which consists trochophora mouth cilia round before losing metamorphosis into adults and begin to operate in the sea benthic life. [Body] division Mollusk's body can generally be divided into three parts head, feet and viscera. ① head In the front end of the body. Agile movement types, head clear differentiation, the birth of their eyes, antennae and other sensory organs, such as snails, snails and squid, etc.; kind of slow head developed, such as chitons; burrowing or sessile species of life, head Ministry has disappeared, such as mussels, oysters and other. ② Foot Usually located in the ventral body for the sport of organs, often due to the animal's life is different, and shapes. Some of the foot was developed leafy, ax-shaped or cylindrical, can crawl or dig sediment; some foot degradation, loss of motor function, such as scallops, etc.; sessile species of life, no foot, such as oysters; some have special foot into the wrist, born head of prey organs, such as squid and octopus, called cephalopods; few types of foot side (ie, side foot parapodium) into special sheet, swimming, called wings or fins, such as pteropods (pteropoda). ③ visceral mass (visceral mass) Where part of the internal organs, often located in the dorsal foot. Most types of offal because symmetrical, but some twisted into a spiral, losing symmetrical shape, such as snails. Mantle (mantle) To stretch the body down from the dorsal skin fold, often wrapped the whole visceral mass. Cavity formed between the mantle and the visceral mass is called the mantle cavity (mantle cavity). Gill cavity often enough and anus, kidney holes, holes and other openings in the raw plant mantle cavity. Mantle epithelium from the outer and inner layers, the outer layer of epithelial secretions, can form a shell, the inner ciliated epithelial cells, cilia, causing the water to make the water cycle in the jacket cavity, in order to complete the respiration, excretion, feeding, etc. About two _set_s of twelve films often heal at the trailing edge, forming a water hole (exhalant siphon) and into the water hole (inhalant siphon). Some species out of the water holes extend into a tube, called the outlet pipe and the outer shell protruding into the pipe. Shell (shell) In vitro with an important feature of mollusk shells, so the study of mollusks and shellfish, also known as school discipline (malacology). Most molluscs have twelve or more shells, not the same shape. Some were cap; snails spiral shape; digging footed tubular; Lamellibranchia petal. Some species of shells degenerate into an inner shell, some shell. Shell has a protective soft body functions. The main component of shells is calcium carbonate and a small amount of the shell matrix (conchiolin or said shell elements) constituting these substances secreted by the epithelial cells formed in the mantle. Shell structure can be divided into 3 layers), the outermost layer of the stratum corneum (periostracum), thin, transparent, glossy, constituted by the shell matrix, without the acid-base erosion, protect shells. The middle layer of the shell (ostracum), also known as the prismatic layer (primatic layer) accounted for most of the shells, the angular calcite (cacalcite) composition. The innermost layer of the shell bottom (hypostracum), namely nacre layer (peral layer), shiny, by the leafy aragonite (aragonite) composition. The outer and middle secreted form of the mantle edge, can be gradually increased with the growth of animals, but not thickened; inner membrane secretion from the entire _set_ can be increased with the growth of the individual thickness. Pearl is the nacre layer. When the mantle by the tiny sand particles and other foreign matter intrusion stimulation of epithelial cells by stimulating foreign body that is at the core and the mantle epithelium into the connective tissue in between, into the epithelial cells divide to form their own pearl sac, sac that secrete nacre , layer by layer, the nuclear complex packet bit gradually formed pearls. According to historical records 2200 years BC, China had fresh sterile beads records (The Book. Yugong articles), Guangxi Autonomous sterile beads famous since ancient times, picking began in the Han Dynasty. Growth and prismatic cuticle layer of the non-continuous, since the food, temperature and other factors affect the secretion function of the mantle, the growth rate is different from the shell, so the shell growth lines formed on the surface, the growth speed is shown. Digestive Mollusc digestive tract developed, a few parasitic species (the send snail entocolax) degradation. Most species within the mouth piece with jaw (mandible) and radula (radula), a jaw piece or in pairs, can assist prey. Molluscan radula is unique organ, the bottom of the oral tongue protruding bits (odontophore) surface, consisting of rows of horny teeth, like Cuodao shape. Radula to scrape food telescopic movement back and forth when feeding. Shape and number of teeth of the pinion tongue, vary between different species, the species identification of important features. Small teeth horizontal composition, composed of many rows of small teeth radula. Each crossbar has a central tooth, a tooth or a number of right and left pair, one pair of edges of the teeth or affinity pair. Arrangement of small teeth tongue tooth to tooth expressed as China round snail (cipangopaludina chinensis) tooth formula 2.1.1.1.2. Body cavity and the circulatory system Secondary body cavity mollusks extreme degradation, the residual lumen circumference and gonads and excretory organs of the heart chamber (pericardinal cavity). Newborn body cavity gap is present in various tissues and organs, there are blood flow, forming a sinusoid (blood sinus). Circulatory system of the heart, blood vessels, sinuses and blood constituents. Cardiac general position dorsal visceral mass pericardial cavity constituted by the atrial and ventricular. A ventricular wall thickness, can Pollex for blood circulation power; appendage one or in pairs, often in line with the number of gills. There are debates between atrial and ventricular film to prevent blood reflux. Arterial and venous vascular differentiation. Arterial blood from the ventricle into the various parts of the body, after importing sinuses, venous return from the atrial appendage, the mollusk is open tubular loop. Some kind of fast swimming, cycling was closed tube. Colorless blood, containing amebocyte. Some species plasma contains hemoglobin (haemoglobin) or hemocyanin (haemocyanin), so the blood is red or blue. Respiratory Aquatic species with gills and gill cavity to coat the surface of epithelial stretch forming, bit cavity. Different forms gills, gill sides of the shaft were born there gill, pinnate, said shield gills; just gave birth gill gill shaft side, was a comb, comb Gill said (ctenidium); some gill flap into shape, said lamellibranch (lamellibranch); extend into some kind of gill filaments. Said filament gill (filibranch). Some of the gills disappear, and the dorsal surface of the skin to give birth to secondary gill (secondary branchium), and some species without gills. Gills in pairs or as a single number varies, ranging from one or a pair, as many as up to tens of right. Species of terrestrial life, no gills. Its tiny blood vessels inside the mantle cavity into a certain area with the formation of dense lungs, can be directly ingested oxygen in the air. This is an adaptation of terrestrial life. Excretory organs Molluscs renal excretory organ pipe is basically consistent with the number of the number of gill general, only a few species of larvae of the original kidney tubes. After the glandular part of the kidney tubes and tubular components, glandular part of the rich blood vessels, kidneys mouth ciliated openings in pericardial cavity; tubular portion of the thin-walled tubes, the inner wall of the ciliated kidney openings in the mantle cavity. Renal not be excluded due to heart tube metabolites, can also exclude blood metabolites. In addition Wai Wai heart gland on the inner wall of the heart, capillaries clouds, metabolites can be excluded in the heart surrounded by the renal tubular excretion. Nervous system No differentiation ganglia nervous system primitive types, only surrounded pharyngeal nerve ring and extending to the body after a pair of foot nerve cord (pedal cord) and a contralateral nerve cord (pleural cord). There are other types of higher four pairs of ganglia, between the nerve ganglia are connected. Brain sections (cerebral ganglion) bit dorsal esophagus, sending nerve to the front of the head and body, the Secretary feeling; foot ganglion (pedal ganglion bit the front foot, stretched nerves to the foot, the Secretary of motor and sensory; side ganglion (peural ganglion) issued nerves to the mantle and gill; dirty ganglia (visceral ganglion) issued to each of the internal organs of these nerve ganglia have tended to focus on the potential, and some types of major ganglion together form. brain, cartilage surrounding the outside, such as cephalopods. mollusk has differentiated antennae, eyes, and balance osphradium capsule and other sensory organs, sensory sensitivity. Reproductive and developmental Molluscs mostly dioecious, many types of sexually dimorphic; are also some of androgyny. Mostly in the form of cleavage cleavage completely uneven, and many are spiral. A small number of incomplete cleavage. Ontogeny by trochophora and veliger (veliger larva) two-stage larvae, larval morphology trochophora and polychaete annelids approximation veliger early development dorsal coat primordia, and secrete shell, There ventral foot primordia develop into the ring before the opening ciliary border membrane (velum) or said face plate. And some kind of direct development. Freshwater mussels have special Glochidia (glochidium). [Species] Molluscs variety, a very wide range of life, seawater, freshwater and terrestrial are produced. Has documented more than 130,000 kinds, second only to arthropods. The structure is further complicated mollusks, function more perfect, they have some of the same characteristics as the annelid: secondary body cavity, the renal tubular, spiral cleavage, ontogeny has trochophora etc. mollusk is therefore considered evolved from annelids toward not very active lifestyle out of an earlier differentiation. Most covered with a variety of in vitro mollusks shells, it is usually also known as shellfish. Since most of them gorgeous shells, meat is delicious, nutritious, and easier to catch, so far in the ancient fishing and hunting period, had been used in humans. Many edible, medicinal, agricultural, arts and crafts industry with, there are some types of toxic and can spread disease, damage crops, damaged harbor construction and transportation facilities, harmful to humans. Including mollusks in life for people familiar gastropods such as snails, snail slug; bivalve mussel, clam, etc.; cephalopods cuttlefish (squid), octopus, etc.; adhesion between the coastal and intertidal rocks multi-plate class chitons and so on. They exist in the form of significant differences, such as their institutional or symmetrical or asymmetrical; surface or shells or shell; shell or 一枚 or 二枚 or more pieces. But according to the study of comparative morphology of extant species studied embryology and biology of ancient fossils had already appeared as early as the Cambrian discovery: All mollusks are built on a basic model structure, the model is It is envisaged that the original mollusk, which is the ancestor of molluscs mode, the original redevelopment mollusks evolved into various different classes. So raw mollusks represent the basic characteristics of all mollusks. According to the research of existing animals, it was envisaged by the original mollusks, before and after the shift change through the body and dorsal-ventral axis of the shaft, foot, visceral sac and coat the cavity to form the structural characteristics of the existing animals of various classes. Molluscs can be divided into seven classes: veneer Gang (monoplacophora), multi-plate Gang (polyplacophora), no plate Gang (aplacophora), gastropods (gastropoda), Bivalvia (bivalvia), dig foot Gang (scaphopoda) , cephalopods (cephalopoda). Which only gastropods and bivalve freshwater species living there, as well as terrestrial gastropods species, which Outlines contains more than 95% of the mollusk species, each of the other classes are marine life. [Origin and Evolution] Origin of molluscs in two different ways: One is that mollusks originated in Platyhelminthes; another think mollusks and annelids are evolved from a common ancestor, but due to their long-term evolutionary process toward a different life way of development, so the final form of two different systems of animals. After an argument the reasons more fully, because many species of marine mollusks during embryonic development in animals have also to many areas as a burden on the larval stage. Coupled with the development of two types of animals have cleavage, in the adult have in common on some transformation. For example, the basic part of the renal excretory organ pipe type, are secondary in the body cavity. This common ancestor, a part of the way toward the development of activities in a manner suitable for the formation of somites, warts and developed enough head, which is part of the animal; another part of the way toward the development of adapted relatively inactive, it creates a protective Housing and construction for many sports use, such as section head or phenomenon and does not appear or degradation. It also developed a number of unique structures mollusks ─ ─ mantle. In each group due to the difference between the larger mollusks, and there is no more obvious differences to explain the genetic relationships among well. In mollusks, the dual classes are relatively primitive nervous because it's symmetrical structure, secondary body cavity is relatively developed, retains the original trapezoidal dual nervous system. Gastropod taxa is relatively low because it has a similar annelid trochophora or similar veliger stage. Lamellibranchia animals most notable feature is the respiratory system gill flap-like gills. In extant mussel, for example, each piece is a flap-like gills gill flap, which is composed of two small flap constitute cheek, on the outside, said outside a small gill flap, on the inside, said a small flap in the cheek. There are many small flap of each cheek gill filaments, the gill surface cilia inside blood vessels, there are many holes. In the space between the gill flap valve with the diaphragm spaced intervals, forming a plurality of gill pipes. Because the cilia swing, water from the inlet pipe into the mantle, there are small holes into the gill gills into the water pipes, and then on up to the gill chamber, and finally through the outlet pipe out of the body. In the water over the course of gill gill blood gas exchange completed within. Such animals have two mantle, which has two halves shell, wide flat bottom of their foot kind of low, creeping line, also appeared during the development trochophora, so they may be similar to a common gastropod ancestors. Body structure cephalopods highly developed brain, eyes, and circulatory systems are the most evolved mollusk, first discovered in the formation of mollusks also cephalopods, may also be due to the fast way to adapt to social activities, rapid evolution toward specialization in the direction of it. [] Relationship with humans Value ① food value Marine abalone, jade snail, conch, conch, Babylonia, snail, cockles, mussels, scallops, Pinna, oysters, clams, clams, clams, razor clams, squid, squid, octopus, fresh water production snail, snail, mussels, clams, snails and other terrestrial habitats meat is delicious, with a high nutritional value. ② medicinal value Abalone shell (abalone medicine called), called Morinda baby shells, pearls, shells called Cuttlebone squid and clams, oysters, clams, clam shells, etc., etc. are commonly used herbs in Chinese medicine. From abalone, conch, sea snails, clams, oysters, squid and other antibiotics and anticancer drugs can be extracted. ③ agricultural value Yield more small mollusks can be done farmland fertilizer or feed, river clams can be reared freshwater fish. ④ industrial use. Mollusk shells of burnt lime is good raw materials. Thicker nacre shells (such as mussels, snails horseshoe, etc.) are made of materials buttons. ④ craft or decorative use Many shellfish shells have a unique shape and pattern, shiny, colorful, ancient and modern people like to collect enjoying the goods. ⑤ Geological value There are many doors as mollusks indicate depositional environment refers to the phase fossils in geological history. China in the world and the bottom of the Cambrian, there veneer Gang and other fossil mollusks appear, many ammonites became the Mesozoic intercontinental range division, compared with fossil strata, and some can be used to understand the ancient water temperature and salinity, etc.; snail fossils reflect Quaternary climate. Harm to humans Terrestrial snails, slugs eat plants such as leaves, buds, harm vegetables, fruit, tobacco, etc.; ocean some carnivorous species can kill oysters, cockles and other mud seedlings, resulting in the loss of farmed bivalves; Some herbivorous species eat kelp, seaweed seedlings, breeding algae predators. In freshwater and terrestrial molluscs, Lymnaea is the intermediate host of Fasciola beans are Clonorchis sinensis snail intermediate hosts, flat roll snail intermediate host Fasciolopsis, short trench is curled Paragonimus intermediate host, the snail intermediate host of Schistosoma japonicum, very serious harm to humans. Ocean ship maggots, sea bamboo shoots are specialized types of wood or rock Chuanzao burrowing, for ocean vessel, wooden stakes and the harbor, stone building has hazards. Camp attached or sessile species often attached to the bottom a lot, can affect the speed of the vessel sailed. Some species live attached, can clog pipes, affecting production. [Difference between mollusks and crustaceans shells] First, the mollusk shell is secreted by a coat formed by calcareous, except there is no connection joints, their life will not moult. Arthropods in vitro covered with chitin exoskeleton, also known as the epidermis or cuticle. Somites in the joints between adjacent membrane, a very thin cuticle and easy refractive activity. Appendage movable joints. Arthropods in the growth process to regularly molt. Second, the mollusk is a kind of soft-bodied invertebrates matter. Mollusks generally have symmetrical shape, but some mollusks Since the emergence of various strange twist body shape. They often have a shell, no somites, most can be divided into head, feet, visceral sac, etc. 3 parts. The outer layer of skin from the back folds into a film called jacket. Jackets surrounded the body and secrete calcareous. Crustaceans are arthropods door, arthropods constituted by the one body section, sub-section different law can be divided into head, thorax, abdomen 3, or head to head and chest healing chest, abdomen or chest and healing for the trunk , a pair of sub-section appendages on each body segment. Appendages double-and single-branch branch type categories. Circulatory system is an open tube. Aquatic species as gill or respiratory book gills, terrestrial trachea or lungs or both books. Primitive arthropods rely on gas exchange surface. Nervous system is centralized chain of the nervous system. There are touch, taste, smell, hearing, balance and vision and other sensory organs. There are two kinds of eye monocular and compound eyes. Composed of a compound eye eye can perceive objects in motion and shape of the outside world, able to adapt to the intensity of light and distinguish colors. Another great morphological variation crustacean, the smallest class as fierce Daphnia body length of less than 1 mm. The biggest giant spider crab crayfish stretch when two widths up to 4 meters. Takes the shape of a long cylindrical body section of clear, all separately, chest, abdomen 3. Head made from six individual sections healing. Outer skeleton of crustaceans each body segment consists of two parts: the back of a piece of the carapace, ventral plastron piece is. Carapace sides often outside (under) extends to the side armor, appendages on both sides of the students in general plastron. As can be seen arthropods higher than mollusks.
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Overview
Also for mollusc. Invertebrate mollusks door (Mollusca), is in addition to the largest groups of insects outside discrepancy of about 75,000 species. The big difference between the system, but there are common features ︰ soft unsegmented body, usually separately - foot (some heads degraded or disappear; enough muscle mass) and visceral - mantle (the dorsal visceral mass, mantle and the composition of the mantle cavity) in two parts. Dorsal skin fold pleats extending down into the mantle, the mantle wrapped in vitro secretion of calcareous shell (some degenerate into an inner shell or no shell). No real inside bones. The body has a blood chamber (ie, a series expansion of the sinuses). Blood Blood features such as liquid bone cavity to maintain the tension of the body. Star containing a small amount of blood or amoeba-shaped cells. Blood blood ceruloplasmin (gastropods and cephalopods). Mouth muscles contain myoglobin. The real degradation of the body cavity and pericardial cavity reproduction. Surface generally have cilia or mucus. Toothed tongue inside the mouth. Molluscan radula is most peculiar organ, the multi-column horny tooth plates, the shape of the rasp to help feeding. Often large digestive glands. There comb gill surface ciliated for exciting water (potable water in bivalves filter food particles contribute). Renal excretory organs. Marine species excrete ammonia or urea, terrestrial gastropods uricosuric. Hermaphrodite or allogeneic. Cephalopods and gastropods part of in vitro fertilization, hermaphrodites were then cross-fertilization. Several pairs of ganglia. Largest mollusk giant squid wrist expand up to 12 meters (40 feet), and the smallest is only 1 cm long snails. Molluscs distributed in a variety of habitats, such as seawater, freshwater, land (especially woodland, and even dry areas). Some gastropods are the parasites of other animals, mollusks important economic significance. Many aquatic species, especially clams, oysters, scallops and mussels are edible and can be fishing or farming. Large genus of terrestrial snails (Helix) is used as food in Europe. Many shells or pearls can be used as decorations, boat docks and maggots are wooden harm. Some freshwater snail intermediate hosts of parasitic worms. Molluscs (Cephalopod) populations, including squid, octopus, nautilus, and extinct ammonites and arrows stone. It has long tentacles around the mouth to grab prey, moves forward to take advantage of the siphon jet action. Molluscs (Mollusca) is a second door to the animal kingdom. Molluscs are three germ layers, bilaterally symmetrical, with a true animal body cavity. True body cavity is formed by a split molluscs chamber method, a body cavity is formed in the mesoderm. Soft body, usually symmetrical, certain species due to the reverse, inflection, and showed a variety of strange forms. Usually have the shell, no body section, there is enough meat or wrist, there are enough degradation. The outer layer of skin from the back of the jacket folds into a so-called, will surround the body and secrete a protective calcareous shelly. Born gill breathing and body cavity between coats. Land and water are distributed throughout. Including dual nerve Gang (such as chitons), gastropods (such as abalone, snails); dig foot outline (eg angle shellfish), Lamellibranchia (such as cockles, oysters), cephalopods (such as squid, nautilus), etc. . One animal body cavity door. Haraguchi are animals, true body cavity classes end cell dry. Since gastropods become secondary to reverse visceral block of left-right asymmetry, and various other classes of system are symmetrical. Body from head (Lamellibranchia no), foot and visceral blocks. Visceral epidermal extension to form the mantle block, wrapped in the main part of the body. It is the space between the internal organs of the mantle cavity block, there gills, digestive and excretory organs end opening here. No body section structure. In vivo clearance for irregular blood chamber. True body cavity due to narrowed mesenchymal developed form only pericardial cavity, the cavity and the renal tubular lumen gonads (reproductive cavity). Head with eyes and mouth and feeling. As foot movement organs, muscles smooth muscle, which related to its slow movement. Ink twill muscle wall. Mantle outward secretion shells. Different classes in different shells in the number and shape. Digestive tract long, usually toothed tongue and salivary glands in the mouth. Midgut gland opening in the stomach. The gills are generally 1 pair, corresponding to 2 appendage a heart ventricle. But in cephalopods with two pairs of species in the gills there are four atrial appendage. Gastropods because visceral block reverse, some only one of the gill (1 appendage a heart ventricle), and some species disappear and the wake is replaced coat gills. Terrestrial gastropod snails in the lung, part of its mantle has evolved into the lungs. To open vascular system, respiratory pigment hemocyanin mostly. Clams, snails and other flat volume compared with hemoglobin. Renal excretion is to pipe (Bao Yena's devices) based, but there's a Kaibo's species (bivalves). Nervous system as a particular type, in addition to a head on esophageal ganglia, also has side ganglia, ganglia and dirty foot ganglion each one right. Each pair of the same nerve ganglion by the cross ties and other head ganglion nerve ganglia linked by a vertical. Hermaphrodite or allogeneic. In the male, the ship maggots and abalone, etc., see the sexual conversion. Apart from cephalopods, underwent spiral cleavage by trochophora larval period and the face plate; But the cleavage of cephalopods is symmetrically direct development. Body structure of molluscs
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The main features
Molluscs morphology large variation, but the basic structure is the same. Soft body with a hard shell, the body hidden in the shell, in order to be protected, because the crust would hinder activity, so their actions are quite slow. Unsegmented, can be divided into head, feet, viscera of three parts, extracorporeal membrane quilt, often secrete shells. Foot is shaped like an ax, with two shells, such as male. People speculated that the original mollusks appear Precambrian, living in shallow, oval body, the body length of not more than 1cm, symmetrical on both sides of the head at the front, with a pair of antennae, base of antennae eye. Ventral body flat, full of muscle mass, form suitable for crawling foot. The back of the body is covered with a coat of convex shell (shell), to protect the entire body. May initially be formed from only the shell of keratin called shell elements (conchiolin), after the deposition of calcium carbonate on the shell element, increasing its hardness. The following is a shell structure of the membrane bilayer of the cell to the ventral body wall extending from the formation, said mantle (mantle) (or pallium), it has a strong secretory capacity, i.e. the shell is formed by the mantle. Under the mantle covered with visceral sac. The rear end of the body, the top of the foot there between a cavity and the visceral sac, is the outer chamber (mantle cavity), which communicates with the outside. There are many on the mantle cavity rows of gill respiration, as well as renal, anal, genital pore openings. Raw molluscan gill structure may be similar in extant gastropods gills, it is by a long gill extending axially alternating sides of the triangle composed of gill filaments, which called comb gill gill (ctenidium). Gill axis extending outward from the mantle or body wall, which contains blood vessels, muscles and nerves, the leading edge of the gill filaments (ie, ventral margin) with bone support chitin rods to increase the hardness of the gills. Gill coat both sides of the back cavity, respectively, intraperitoneal fixed position, and therefore the outer gill cavity into upper and lower chambers. Water from the lower chamber flows into the rear chamber jacket by gill surface and the ventricular outflow mantle cavity, gill leading edge and surface covered with cilia, causing water to flow in the mantle cavity of the swinging cilia. Gill shaft with two vessels, into the back of gill blood vessels (afferentblood vessel), the ventral edge of the gill blood vessels (efferent blood vessel), the flow of blood from the blood vessels into the gill gill blood vessels, but also by the gill surface directly microvascular flows from the ventral edge of the back edge so that the flow direction opposite the flow direction of the gill surface, the gas can be more efficiently exchanged. Like many extant original mollusk species, like the gill surface covered with cilia not only its mantle and skin (including the skin of the foot) portion of the cloth have cilia, swing these cilia cause constant water flow through, in order to facilitate the exchange of gases and prey, the original skin respiration in molluscs is very important. Cilia movement of the foot joint and muscle contraction also constitute the body's movement. Raw mollusks may be herbivorous, feeding on algae growing shallow rocks. Have the same feeding mollusks existing structure. The port is located in front of the head, mouth after oral (buccal cavity), the rear end of a bag-shaped mouth radula sac (radulasac). The bottom of the radula sac membrane with a forward and backward activities to bring the distribution of the film take place in a row, neatly arranged chitin fine-tooth, tooth tip backwards, film tapes and constitutes radula teeth (radula), radula at the bottom of the bag has a radula cartilage (odontophora), attached to the tongue and teeth cartilage extensor (protractor muscle) and muscle contraction (retractormuscle), by stretching muscles, cartilage, and can be extended extraoral film tape to scrape food, Since feeding wear thin front teeth missing aging, the film with the back-end can continue to secrete complement the new gear, which substitute daily rate is the number of rows of many mollusks. This radula of mollusks in most of the existing structure is there. On the back of the mouth opening with a pair of salivary glands, which can smooth radula secretions and food particles into the mouth sticking together to form a food rope, cord food into the stomach via the esophagus. Hemispherical front of the stomach, the side of the inner wall of the stomach with chitin plates, called Dun stomach (gastric shield), the opposite side of the ridge and the formation of many small ditch, the ditch with cilia, called the screening area (sorting region ). The second half of the stomach into the cystic sac called crystal rods (style sac), because of which there is a gelatinous rod structure, called crystal rods (crystalline), the inner wall of the bag also has a crystal rod folds and cilia, also formed cilia ditch. After the food in the mouth sticky mucus forming foods cable is continuously into the stomach, relying on gastric acid (pH value of gastric juice extant species is generally 5-6) to remove the sticky foods cable, making cable free of food particles, Meanwhile screened by ciliary action of the stomach region were screened for food, tiny food particles through the digestive gland of the upper end of the tube into the stomach digestive gland, the gland is food digestion and absorption of intracellular spaces; larger food particles in the stomach was performed extracellular digestion; unable to digest food through the stomach and into the intestine folds, then digestion by the intestinal part of the final form of fecal pellets in the gut. Anal opening in the mantle cavity back end, formed fecal pellets of reducing pollution to the mantle cavity of fecal pellets excreted by the water. Raw molluscan body cavity located in the back of the body, which surrounds the heart and part of the intestine, so in fact represent the pericardial cavity and confining dirty. Cardiac ventricle and the rear end includes a pair of distal end of the atrial appendage from the ventricle through the branch arteries through the formation of small blood vessels, and finally into the tissue is formed in the gap between the sinusoid, and then pooled into a vein sinus, through the kidney, gill blood is flowing atrial and ventricular, this is an open loop. Blood contains deformed cells and respiratory pigment, mainly respiratory pigment hemocyanin (hemocyanin). Excretory organs as the kidneys, located on both sides of pericardial cavity, renal end communicates with the pericardial cavity called the renal mouth (nephrostome), end with the outside world, known outside the kidney hole (nephridiopore). Pericardial accepted by the heart and pericardial glands release of metabolites, with pericardial fluid from the mouth into the kidneys kidney, kidney has the ability to absorb a certain weight, it will be useful salts recycling, waste becomes useless into the urine, kidney hole through the outer jacket chamber and then excreted. Neural structures of the original mollusk is very simple around the esophagus to form a nerve ring, two pairs separated by a nerve ring nerve cord, a symmetrical foot ventral nerve cord (pedal cord), disposable foot muscle contraction; back of a symmetric splanchnic nerve cord (visceral cord), govern the movement of internal organs and jackets. According to the existing molluscs speculated may also include a sensory eye, a pair of balanced balloon (statocyst) inside the foot, and a pair osphradium (osphradia), which is located under the gill membranes, is a chemical receptors. Reproductive system includes a pair of gonads, located pericardial front in the back, dioecious, no reproductive ducts, sperm or eggs mature released into the pericardial cavity, as part of the gonad cavity is also a body cavity, so the germ cells by pericardial cavity, and then routed through the kidneys in vitro. Fertilization occurs in seawater, raw molluscan embryos may be very similar to the existing molluscs, also typical spiral cleavage, blastocyst formation hole oral, formed after gastrulation trochophora (trochophore). Trochophora was pear-shaped, with a typical cilia cilia before opening round (prototroch), in the upper part of the body around the mouth, when the first four collective cleavage are at the top, as well as the top beam. Trochophora not only in mollusks, also appears in the annelid. The original species development after only trochophora, most existing mollusks trochophora a very short period, and subsequently into veliger stage (veliger larva). Face plate appears full, shell, viscera and other structures when the larvae. Speculated that the original did not face plate mollusk larvae, which consists trochophora mouth cilia round before losing metamorphosis into adults and begin to operate in the sea benthic life.
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Division of the body
Mollusk's body can generally be divided into three parts head, feet and viscera. ① head In the front end of the body. Agile movement types, head clear differentiation, the birth of their eyes, antennae and other sensory organs, such as snails, snails and squid, etc.; kind of slow head developed, such as chitons; burrowing or sessile species of life, head Ministry has disappeared, such as mussels, oysters and other. ② Foot Usually located in the ventral body for the sport of organs, often due to the animal's life is different, and shapes. Some of the foot was developed leafy, ax-shaped or cylindrical, can crawl or dig sediment; some foot degradation, loss of motor function, such as scallops, etc.; sessile species of life, no foot, such as oysters; some have special foot into the wrist, born head of prey organs, such as squid and octopus, called cephalopods; few types of foot side (ie, side foot parapodium) into special sheet, swimming, called wings or fins, such as pteropods (Pteropoda). ③ visceral mass (visceral mass) Where part of the internal organs, often located in the dorsal foot. Most types of offal because symmetrical, but some twisted into a spiral, losing symmetrical shape, such as snails. Mantle (mantle) To stretch the body down from the dorsal skin fold, often wrapped the whole visceral mass. Cavity formed between the mantle and the visceral mass is called the mantle cavity (mantle cavity). Gill cavity often enough and anus, kidney holes, holes and other openings in the raw plant mantle cavity. Mantle epithelium from the outer and inner layers, the outer layer of epithelial secretions, can form a shell, the inner ciliated epithelial cells, cilia, causing the water to make the water cycle in the jacket cavity, in order to complete the respiration, excretion, feeding, etc. About two _set_s of twelve films often heal at the trailing edge, forming a water hole (exhalant siphon) and into the water hole (Inhalant siphon). Some species out of the water holes extend into a tube, called the outlet pipe and the outer shell protruding into the pipe. Shell (Shell) In vitro with an important feature of mollusk shells, so the study of mollusks and shellfish, also known as school discipline (Malacology). Most molluscs have twelve or more shells, not the same shape. Some were cap; snails spiral shape; digging footed tubular; Lamellibranchia petal. Some species of shells degenerate into an inner shell, some shell. Shell has a protective soft body functions. The main component of shells is calcium carbonate and a small amount of the shell matrix (conchiolin or said shell elements) constituting these substances secreted by the epithelial cells formed in the mantle. Shell structure can be divided into 3 layers), the outermost layer of the stratum corneum (periostracum), thin, transparent, glossy, constituted by the shell matrix, without the acid-base erosion, protect shells. The middle layer of the shell (ostracum), also known as the prismatic layer (primatic layer) accounted for most of the shells, the angular calcite (cacalcite) composition. The innermost layer of the shell bottom (hypostracum), namely nacre layer (peral layer), shiny, by the leafy aragonite (aragonite) composition. The outer and middle secreted form of the mantle edge, can be gradually increased with the growth of animals, but not thickened; inner membrane secretion from the entire _set_ can be increased with the growth of the individual thickness. Pearl is the nacre layer. When the mantle by the tiny sand particles and other foreign matter intrusion stimulation of epithelial cells by stimulating foreign body that is at the core and the mantle epithelium into the connective tissue in between, into the epithelial cells divide to form their own pearl sac, sac that secrete nacre , layer by layer, the nuclear complex packet bit gradually formed pearls. According to historical records 2200 years BC, China had fresh sterile beads records (The Book. Yugong articles), Guangxi Autonomous sterile beads famous since ancient times, picking began in the Han Dynasty. Growth and prismatic cuticle layer of the non-continuous, since the food, temperature and other factors affect the secretion function of the mantle, the growth rate is different from the shell, so the shell growth lines formed on the surface, the growth speed is shown. Digestive Mollusc digestive tract developed, a few parasitic species (the send snail Entocolax) degradation. Most species within the mouth piece with jaw (mandible) and radula (radula), a jaw piece or in pairs, can assist prey. Molluscan radula is unique organ, the bottom of the oral tongue protruding bits (odontophore) surface, consisting of rows of horny teeth, like Cuodao shape. Radula to scrape food telescopic movement back and forth when feeding. Shape and number of teeth of the pinion tongue, vary between different species, the species identification of important features. Small teeth horizontal composition, composed of many rows of small teeth radula. Each crossbar has a central tooth, a tooth or a number of right and left pair, one pair of edges of the teeth or affinity pair. Arrangement of small teeth tongue tooth to tooth expressed as China round snail (Cipangopaludina chinensis) tooth formula 2.1.1.1.2. Body cavity and the circulatory system Secondary body cavity mollusks extreme degradation, the residual lumen circumference and gonads and excretory organs of the heart chamber (pericardinal cavity). Newborn body cavity gap is present in various tissues and organs, there are blood flow, forming a sinusoid (blood sinus). Circulatory system of the heart, blood vessels, sinuses and blood constituents. Cardiac general position dorsal visceral mass pericardial cavity constituted by the atrial and ventricular. A ventricular wall thickness, can Pollex for blood circulation power; appendage one or in pairs, often in line with the number of gills. There are debates between atrial and ventricular film to prevent blood reflux. Arterial and venous vascular differentiation. Arterial blood from the ventricle into the various parts of the body, after importing sinuses, venous return from the atrial appendage, the mollusk is open tubular loop. Some kind of fast swimming, cycling was closed tube. Colorless blood, containing amebocyte. Some species plasma contains hemoglobin (haemoglobin) or hemocyanin (haemocyanin), so the blood is red or blue. Respiratory Aquatic species with gills and gill cavity to coat the surface of epithelial stretch forming, bit cavity. Different forms gills, gill sides of the shaft were born there gill, pinnate, said shield gills; just gave birth gill gill shaft side, was a comb, comb Gill said (ctenidium); some gill flap into shape, said lamellibranch (lamellibranch); extend into some kind of gill filaments. Said filament gill (filibranch). Some of the gills disappear, and the dorsal surface of the skin to give birth to secondary gill (secondary branchium), and some species without gills. Gills in pairs or as a single number varies, ranging from one or a pair, as many as up to tens of right. Species of terrestrial life, no gills. Its tiny blood vessels inside the mantle cavity into a certain area with the formation of dense lungs, can be directly ingested oxygen in the air. This is an adaptation of terrestrial life. Excretory organs Molluscs renal excretory organ pipe is basically consistent with the number of the number of gill general, only a few species of larvae of the original kidney tubes. After the glandular part of the kidney tubes and tubular components, glandular part of the rich blood vessels, kidneys mouth ciliated openings in pericardial cavity; tubular portion of the thin-walled tubes, the inner wall of the ciliated kidney openings in the mantle cavity. Renal not be excluded due to heart tube metabolites, can also exclude blood metabolites. In addition Wai Wai heart gland on the inner wall of the heart, capillaries clouds, metabolites can be excluded in the heart surrounded by the renal tubular excretion. Nervous system No differentiation ganglia nervous system primitive types, only surrounded pharyngeal nerve ring and extending to the body after a pair of foot nerve cord (pedal cord) and a contralateral nerve cord (pleural cord). There are other types of higher four pairs of ganglia, between the nerve ganglia are connected. Brain sections (cerebral ganglion) bit dorsal esophagus, sending nerve to the front of the head and body, the Secretary feeling; foot ganglion (pedal ganglion bit the front foot, stretched nerves to the foot, the Secretary of motor and sensory; side ganglion (peural ganglion) issued nerves to the mantle and gill; dirty ganglia (visceral ganglion) issued to each of the internal organs of these nerve ganglia have tended to focus on the potential, and some types of major ganglion together form. brain, cartilage surrounding the outside, such as cephalopods. mollusk has differentiated antennae, eyes, and balance osphradium capsule and other sensory organs, sensory sensitivity. Reproductive and developmental Molluscs mostly dioecious, many types of sexually dimorphic; are also some of androgyny. Mostly in the form of cleavage cleavage completely uneven, and many are spiral. A small number of incomplete cleavage. Ontogeny by trochophora and veliger (veliger larva) two-stage larvae, larval morphology trochophora and polychaete annelids approximation veliger early development dorsal coat primordia, and secrete shell, There ventral foot primordia develop into the ring before the opening ciliary border membrane (velum) or said face plate. And some kind of direct development. Freshwater mussels have special Glochidia (glochidium).
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Species
Molluscs variety, a very wide range of life, seawater, freshwater and terrestrial are produced. Has documented more than 130,000 kinds, second only to arthropods. The structure is further complicated mollusks, function more perfect, they have some of the same characteristics as the annelid: secondary body cavity, the renal tubular, spiral cleavage, ontogeny has trochophora etc. mollusk is therefore considered evolved from annelids toward not very active lifestyle out of an earlier differentiation. Most covered with a variety of in vitro mollusks shells, it is usually also known as shellfish. Since most of them gorgeous shells, meat is delicious, nutritious, and easier to catch, so far in the ancient fishing and hunting period, had been used in humans. Many edible, medicinal, agricultural, arts and crafts industry with, there are some types of toxic and can spread disease, damage crops, damaged harbor construction and transportation facilities, harmful to humans. Including mollusks in life for people familiar gastropods such as snails, snail slug; bivalve mussel, clam, etc.; cephalopods cuttlefish (squid), octopus, etc.; adhesion between the coastal and intertidal rocks multi-plate class chitons and so on. They exist in the form of significant differences, such as their institutional or symmetrical or asymmetrical; surface or shells or shell; shell or 一枚 or 二枚 or more pieces. But according to the study of comparative morphology of extant species studied embryology and biology of ancient fossils had already appeared as early as the Cambrian discovery: All mollusks are built on a basic model structure, the model is It is envisaged that the original mollusk, which is the ancestor of molluscs mode, the original redevelopment mollusks evolved into various different classes. So raw mollusks represent the basic characteristics of all mollusks. According to the research of existing animals, it was envisaged by the original mollusks, before and after the shift change through the body and dorsal-ventral axis of the shaft, foot, visceral sac and coat the cavity to form the structural characteristics of the existing animals of various classes. Molluscs can be divided into seven classes: veneer Gang (Monoplacophora), multi-plate Gang (Polyplacophora), no plate Gang (Aplacophora), gastropods (Gastropoda), Bivalvia (Bivalvia), dig foot Gang (Scaphopoda) , cephalopods (Cephalopoda). Which only gastropods and bivalve freshwater species living there, as well as terrestrial gastropods species, which Outlines contains more than 95% of the mollusk species, each of the other classes are marine life.
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Origin and Evolution
Origin of molluscs in two different ways: One is that mollusks originated in Platyhelminthes; another think mollusks and annelids are evolved from a common ancestor, but due to their long-term evolutionary process toward a different life way of development, so the final form of two different systems of animals. After an argument the reasons more fully, because many species of marine mollusks during embryonic development in animals have also to many areas as a burden on the larval stage. Coupled with the development of two types of animals have cleavage, in the adult have in common on some transformation. For example, the basic part of the renal excretory organ pipe type, are secondary in the body cavity. This common ancestor, a part of the way toward the development of activities in a manner suitable for the formation of somites, warts and developed enough head, which is part of the animal; another part of the way toward the development of adapted relatively inactive, it creates a protective Housing and construction for many sports use, such as section head or phenomenon and does not appear or degradation. It also developed a number of unique structures mollusks ─ ─ mantle. In each group due to the difference between the larger mollusks, and there is no more obvious differences to explain the genetic relationships among well. In mollusks, the dual classes are relatively primitive nervous because it's symmetrical structure, secondary body cavity is relatively developed, retains the original trapezoidal dual nervous system. Gastropod taxa is relatively low because it has a similar annelid trochophora or similar veliger stage. Lamellibranchia animals most notable feature is the respiratory system gill flap-like gills. In extant mussel, for example, each piece is a flap-like gills gill flap, which is composed of two small flap constitute cheek, on the outside, said outside a small gill flap, on the inside, said a small flap in the cheek. There are many small flap of each cheek gill filaments, the gill surface cilia inside blood vessels, there are many holes. In the space between the gill flap valve with the diaphragm spaced intervals, forming a plurality of gill pipes. Because the cilia swing, water from the inlet pipe into the mantle, there are small holes into the gill gills into the water pipes, and then on up to the gill chamber, and finally through the outlet pipe out of the body. In the water over the course of gill gill blood gas exchange completed within. Such animals have two mantle, which has two halves shell, wide flat bottom of their foot kind of low, creeping line, also appeared during the development trochophora, so they may be similar to a common gastropod ancestors. Body structure cephalopods highly developed brain, eyes, and circulatory systems are the most evolved mollusk, first discovered in the formation of mollusks also cephalopods, may also be due to the fast way to adapt to social activities, rapid evolution toward specialization in the direction of it.
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And human relations
Value ① food value Marine abalone, jade snail, conch, conch, Babylonia, snail, cockles, mussels, scallops, Pinna, oysters, clams, clams, clams, razor clams, squid, squid, octopus, fresh water production snail, snail, mussels, clams, snails and other terrestrial habitats meat is delicious, with a high nutritional value. ② medicinal value Abalone shell (abalone medicine called), called Morinda baby shells, pearls, shells called Cuttlebone squid and clams, oysters, clams, clam shells, etc., etc. are commonly used herbs in Chinese medicine. From abalone, conch, sea snails, clams, oysters, squid and other antibiotics and anticancer drugs can be extracted. ③ agricultural value Yield more small mollusks can be done farmland fertilizer or feed, river clams can be reared freshwater fish. ④ industrial use. Mollusk shells of burnt lime is good raw materials. Thicker nacre shells (such as mussels, snails horseshoe, etc.) are made of materials buttons. ④ craft or decorative use Many shellfish shells have a unique shape and pattern, shiny, colorful, ancient and modern people like to collect enjoying the goods. ⑤ Geological value There are many doors as mollusks indicate depositional environment refers to the phase fossils in geological history. China in the world and the bottom of the Cambrian, there veneer Gang and other fossil mollusks appear, many ammonites became the Mesozoic intercontinental range division, compared with fossil strata, and some can be used to understand the ancient water temperature and salinity, etc.; snail fossils reflect Quaternary climate. Harm to humans Terrestrial snails, slugs eat plants such as leaves, buds, harm vegetables, fruit, tobacco, etc.; ocean some carnivorous species can kill oysters, cockles and other mud seedlings, resulting in the loss of farmed bivalves; Some herbivorous species eat kelp, seaweed seedlings, breeding algae predators. In freshwater and terrestrial molluscs, Lymnaea is the intermediate host of Fasciola beans are Clonorchis sinensis snail intermediate hosts, flat roll snail intermediate host Fasciolopsis, short trench is curled Paragonimus intermediate host, the snail intermediate host of Schistosoma japonicum, very serious harm to humans. Ocean ship maggots, sea bamboo shoots are specialized types of wood or rock Chuanzao burrowing, for ocean vessel, wooden stakes and the harbor, stone building has hazards. Camp attached or sessile species often attached to the bottom a lot, can affect the speed of the vessel sailed. Some species live attached, can clog pipes, affecting production.
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The difference between mollusks and crustaceans shells
First, the mollusk shell is secreted by a coat formed by calcareous, except there is no connection joints, their life will not moult. Arthropods in vitro covered with chitin exoskeleton, also known as the epidermis or cuticle. Somites in the joints between adjacent membrane, a very thin cuticle and easy refractive activity. Appendage movable joints. Arthropods in the growth process to regularly molt. Second, the mollusk is a kind of soft-bodied invertebrates. Mollusks generally have symmetrical shape, but some mollusks Since the emergence of various strange twist body shape. They often have a shell, no somites, most can be divided into head, feet, visceral sac, etc. 3 parts. The outer layer of skin from the back folds into a film called jacket. Jackets surrounded the body and secrete calcareous. Crustaceans are arthropods door, arthropods constituted by the one body section, sub-section different law can be divided into head, thorax, abdomen 3, or head to head and chest healing chest, abdomen or chest and healing for the trunk , a pair of sub-section appendages on each body segment. Appendages double-and single-branch branch type categories. Circulatory system is an open tube. Aquatic species as gill or respiratory book gills, terrestrial trachea or lungs or both books. Primitive arthropods rely on gas exchange surface. Nervous system is centralized chain of the nervous system. There are touch, taste, smell, hearing, balance and vision and other sensory organs. There are two kinds of eye monocular and compound eyes. Composed of a compound eye eye can perceive objects in motion and shape of the outside world, able to adapt to the intensity of light and distinguish colors. Another great morphological variation crustacean, the smallest class as fierce Daphnia body length of less than 1 mm. The biggest giant spider crab crayfish stretch when two widths up to 4 meters. Takes the shape of a long cylindrical body section of clear, all separately, chest, abdomen 3. Head made from six individual sections healing. Outer skeleton of crustaceans each body segment consists of two parts: the back of a piece of the carapace, ventral plastron piece is. Carapace sides often outside (under) extends to the side armor, appendages on both sides of the students in general plastron. As can be seen arthropods higher than mollusks.
shellfish