mollusc

edit

Also known as mollusks. Mollusks are the largest group except arthropods, with about 654.38+million species.

gingkgo

mollusc

Latin scientific name

Giranus

boundary

animal kingdom

door

Molluscs

catalogue

1 Introduction

Two main characteristics

3 body division

brief introduction

head

foot

visceral mass

4 mantle

Five shells

6 digestive system

Seven-cycle system

Eight respiratory organs

Nine excretory organs

10 nervous system

1 1 reproductive development

12 category

brief introduction

gastropoda

bivalvia

Cephalopoda

Digging poda

Plate-free class

Polyplacophora

Monoptera

Tail cavity stage

The Origin and Evolution of 13

14 available values

Edible

Medicinal value

Agricultural value

Used for craft or decoration.

Geological value

15 is harmful to people.

16 correlation difference

brief introduction

edit

The system is very different, but it has the same characteristics: the body is soft and not segmented, and it is generally divided into feet (some heads degenerate or disappear; Foot muscle) and viscera-sleeve (composed of dorsal visceral mass, sleeve and sleeve cavity). The skin folds on the back extend downward to the mantle, which secretes calcium shells wrapped in the body (some degenerate into inner shells or no shells). There is no real endoskeleton. There is a blood cavity (a series of dilated venous sinuses) in the body. The blood cavity plays the role of liquid bone and maintains the tension of the body. Blood contains a small number of astrocytes or amoeba cells. Blood contains hemocyanin (gastropods and cephalopods). Oral muscles contain myoglobin. The real body cavity degenerates into reproductive cavity and pericardial cavity. There are cilia or mucus on the body surface. A toothed tongue in the mouth. Tooth tongue is a unique organ of most mollusks, which is composed of rows of horny tooth plates and looks like a file to help feed. There are often large digestive glands. Comb gills with cilia on the surface, used to stimulate water flow (in bivalves, it helps to filter food particles in water). The excretory organ is the kidney. Marine species excrete ammonia or urea, and terrestrial gastropods excrete uric acid. Androgyny or heterogamy. Cephalopods and some gastropods are fertilized in vitro, while hermaphrodites are fertilized by cross-fertilization. There are several pairs of ganglia. The largest mollusk is the king squid, whose wrist is 12 meters (40 feet), and the smallest is a snail, with a length of only 1 cm. Molluscs are distributed in various habitats, such as seawater, fresh water and land (especially woodland and even arid areas). Some gastropods are parasites of other animals, and mollusks have important economic significance. Many aquatic species, especially clams, oysters, scallops and mussels, are edible and can be caught or cultured. Snails are regarded as delicacies in Europe. Many shells or pearls can be used as decorations, and ship maggots are harmful to docks and wooden boats. Some freshwater snails are intermediate hosts of parasites.

Body structure diagram of mollusk

Cephalopods include squid, octopus, nautilus and extinct ammonites and arrowstones. It has long tentacles near its mouth to catch prey, and it moves by spraying water with a siphon.

octopus

Mollusks are the animal kingdom.

cuttlefish

The second door in the middle. Mollusks are animals with three germ layers, bilateral symmetry and true coelom. The real body cavity of mollusks is formed by the split cavity method, that is, the body cavity of mesoderm body form is soft and generally symmetrical, and some species take on various strange shapes due to twisting and bending. There are usually shells, joints, fleshy feet or wrists, and some degenerated feet. The outer skin folds from the back into a so-called coat, which wraps the body and secretes a protective calcium shell. Breathing gills are born in the cavity between the coat and the body. It is distributed on land and in water. Including polypod (such as soft-shelled turtle) and gastropod (such as abalone and snail); There are seven categories: Digpoda (such as Ceratophyllum), Claphabranchia (such as clams and oysters), Cephalopoda (such as squid and nautilus), Formicidae and Monoptera (such as Neoptera).

Golden snail

Coelenterata. It belongs to protozoa, eukaryotes and terminal stem cells. Gastropoda is quadratic left-right asymmetry due to the torsion of visceral mass, while other systems are left-right symmetry. The body consists of head (apetalous gills), feet and internal organs. The epidermis of the visceral mass extends to form the mantle, which wraps the main part of the body. The space between it and the visceral mass is a cavity with gills inside, where the ends of digestive organs and excretory organs open. There is no joint structure at all. The irregular space in the body is the blood cavity. The true cavity is narrowed due to the development of stroma, and only pericardial cavity, renal lumen and gonadal cavity (reproductive cavity) are formed. There are sensory organs in the head, such as eyes and mouth. As a motor organ, the muscle of foot is smooth muscle, which is related to its slow movement. There are twill muscles on the wall of the ink sac. The mantle secretes shells outward. The number and shape of shells vary from class to class. The digestive tract is long, and there are teeth, tongue and salivary glands in the mouth. The midgut gland leads to the stomach. Generally, there are 1 pairs of gills, and the corresponding heart is 2 auricles 1 ventricle. However, among cephalopods, species with two pairs of gills have four auricles. Gastropoda has only one primary gill (heart is 1 auricle 1 ventricle) due to the torsion of visceral mass, and some species have all disappeared and replaced by external gill. Part of the mantle of spirochetes in terrestrial gastropods has evolved into lungs. It is an open vascular system, and the respiratory pigment is mostly hemocyanin. Cannabis, snails, etc. There is hemoglobin. The excretory apparatus is mainly renal duct (Bowel's organ), but there are also some species with Keber's organ (Claudiobranchia). The nervous system is a special type, with 1 pair in the esophagus, and 1 pair in the pleural ganglion, the foot ganglion and visceral ganglion. Each pair of similar ganglia is connected by transverse nerve, and the cephalic ganglion is connected with other ganglia by longitudinal nerve. Androgyny or heterogamy. Sexual transformation can be seen in stags, ship maggots and abalone. Except Cephalopods, all the others went through spiral division, trochophore stage and panel larva stage. The cleavage of cephalopods is symmetrical and develops directly.

Mollusks are a kind of invertebrates, which are numerous and varied. There are1.2000 species of modern species and fossil species found, which are second only to arthropods and become the second largest species in the animal kingdom. Mollusks are widely distributed and have strong adaptability. There are a large number of members in land, fresh water and salt water, such as snails, mussels, conchs and squid, all of which are familiar representatives. [ 1]

Although various mollusks have different shapes and habits, their basic characteristics are very similar. Most of them are soft and unsegmented, generally divided into four parts: head, feet, visceral mass and mantle. The mantle usually secretes a calcareous hard shell to protect the outside of the body. Because the shape of the mantle varies from species to species, the hard shell shape of mollusks of different species is also different. But except for most adult gastropods, their shells are symmetrical, that is, symmetrical. According to these differences in hard shell and soft structure, scientists divide mollusks into 65,438+00 classes, namely, Monoptera, Polypoda, Echinopoda, Gastropoda, Bivalves, Coccidae, Cephalopoda, Shi Gang and Leptospira. [ 1]

One-legged mollusks are characterized by shells shaped like hats or spoons. They appeared as early as the early CAMBRIAN and have been breeding until modern times, and modern Xinli North is the representative. [ 1]

The body of Polypodiaceae is symmetrical and oval, and its back shell consists of 8 bone plates. They appeared in the late CAMBRIAN and continued until modern times. [ 1]

Without a bone plate and a shell, a symmetrical body is like a bug. But their bodies are covered with horny skin with calcareous needles, so they can also play a certain protective role. Anban is not represented by fossils, but there are sea rabbits in modern life. [ 1]

Gastropoda is a well-known mollusk, and snails, snails and shells are all members of this class. Their software and shells are twisted during individual development, so the shell shape is single spiral. Gastropods also appeared as early as the early CAMBRIAN, and have been multiplying until modern times. They are distributed in land, sea and fresh water. [ 1]

Digpoda's shell is like a slender tube, with open ends and symmetrical sides. Digpoda appeared from Ordovician and continued to modern times, representing animals such as horned shells.

Bivalves are also mollusks that we are familiar with. Mussels, sea fans, clams and most shells that we can find on the seashore belong to bivalves. They are characterized by a hinge structure between the two shells. Their soft parts lack obvious heads, while their bellies have fleshy feet. From CAMBRIAN to modern times, bivalves have been distributed in the oceans and fresh water on the earth. [ 1]

The shell of Coccidoidea also seems to have two petals, but there is no hinge structure. Their shells are actually single shells in the form of "pseudo-double shells". They are extinct paleontologists, living only from Cambrian to Ordovician, representing Hailaert shells and so on.

Cephalopod is the most well-developed and advanced class of mollusks, including nautilus, rod stone, ammonite, arrow stone, modern octopus, squid, etc., which once flourished and had great significance in geological history. They are all carnivores in the ocean and are good at crawling or swimming in the water. Cephalopods are symmetrical on both sides, with an obvious head in front of the body, large developed eyes on both sides, a mouth in the middle and a horny jaw in the mouth; There is a ring around the mouth, which can be used to prey on other animals. Cephalopods have outer shells, inner shells and no shells. Cephalopods also have a long evolutionary history, from CAMBRIAN to modern times. [ 1]

Shigang is an ancient radially symmetrical single cone-shell mollusk, distributed from Ordovician to Devonian, represented by bamboo stone. [ 1]

Soft-tongued snail is also an ancient mollusk, with a single conical shell but symmetrical left and right, distributed from the Cape of Good Hope to Ordovician, representing soft-tongued snail. [ 1]

major feature

edit

mollusc

It is mainly characterized in that: the surface of the soft body has a mantle, and most of them have shells; The moving organ is the foot.

The morphological structure of mollusks is very different, but the basic structure is the same. The body is soft and the shell is hard. The body is protected by hiding in the shell. Because hard shells can hinder activities, they move quite slowly. Without segmentation, it can be divided into three parts: head, feet and visceral mass, which are enveloped in vitro and often secrete shells. The foot is shaped like an axe and has two shells, such as a stallion.

It is speculated that protomolluscs appeared in Precambrian and lived in shallow sea. Its body is oval, its length is less than 1 cm, its two sides are symmetrical, its head is in front, it has a pair of tentacles and its eyes are at the bottom. The abdomen is flat and muscular, forming a foot suitable for crawling. The back of the body is covered with a shield-shaped shell, which protects the whole body. Shells may originally be formed only by keratin, which is called conchiolin. Later, calcium carbonate was deposited on conchiolin, which increased its hardness. Below the shell is a membrane with a double-layer cell structure, which extends from the body wall to the ventral surface. It is called mantle (or mantle), which has strong secretion ability and the shell is formed by mantle. Visceral sac is covered under the mantle. At the back end of the body, there is a cavity between the upper part of the foot and the visceral sac, that is, the mantle cavity, which communicates with the outside world. There are many gills in the coat cavity, as well as the openings of the posterior kidney, anus and genital foramen.

Marine mollusk

The structure of protomollusk gill may be similar to that of existing gastropods. It consists of a long gill and triangular gills alternately protruding from both sides of the gill axis, and is called Chlamys farreri. The branchial axis extends outward from the mantle or body wall containing blood vessels, muscles and nerves. The leading edge (ventral edge) of gill filaments is supported by chitin bone rods to increase the hardness of gills. Branches are fixed by the back and peritoneum on both sides of the sleeve cavity, so the sleeve cavity is divided into upper and lower cavities. Water flows in from the lower cavity at the rear end of the outer jacket cavity, and flows out of the outer jacket cavity through the surface of gill filaments and the upper cavity. The leading edge and surface of gill filaments are covered with cilia, which makes water flow in the lumen of the coat. There are two blood vessels on the branchial axis, the back is the input blood vessel and the abdominal margin is the output blood vessel. Blood flows from the input blood vessels to the branchial blood vessels.

mollusc

The blood vessels flow to the blood vessels outside the gills, and also from the capillaries on the surface of the gill filaments directly from the rear edge to the abdominal edge, so that the direction of blood flow is just opposite to the direction of water flow on the gill surface, and gas exchange can be carried out more effectively.

Protomollusks, like many living species, are covered with cilia not only on the gill surface, but also on the mantle and skin (including the skin of feet). The oscillation of these cilia makes water pass through continuously, which is beneficial to the exchange of gas and predation, so the respiration of skin is very important in protomollusks. The ciliary movement of the feet and the contraction of muscles also combine to form the movement of the body. Protomollusks may be herbivores, feeding on algae growing on rocks in shallow seas. It has the same feeding structure as the existing mollusks. The mouth is located at the front end of the head, followed by the oral cavity, and there is a bag-shaped lingual capsule behind the oral cavity. The bottom of the lingual capsule is a membrane band that can move back and forth. There are rows of neatly arranged chitin fine teeth on the membrane belt, and the tips of the teeth are backward. The membrane band and the teeth form a toothed tongue, and the bottom of the tongue capsule has a odontoid process. The extensor and retractor muscles are attached to the tongue capsule and cartilage. Depending on muscle, cartilage,

Naked gill mollusk

The fine teeth at the front end are gradually aging and falling off, and the back end of the membrane band can continuously secrete new teeth, and the replacement speed is several rows a day in many mollusks. This tongue structure exists in most existing mollusks. There are a pair of salivary gland openings on the back of the mouth, and their secretions can make the tongue smooth, and stick the food particles entering the mouth together to form a food rope, which enters the stomach through the esophagus. The front end of the stomach is hemispherical, and there is a chitin plate on one side of the inner wall of the stomach, which is called gastric shield. The opposite side and cilia form many tiny ridges and grooves, which are called zoning areas. The second half of the stomach is saccate, which is called style sac, because there is a gelatinous rod-like structure called crystal, and there are folds and cilia on the inner wall of the crystal sac, which also forms cilia groove. After the food is adhered by mucus in the oral cavity to form a food rope, it continuously enters the stomach, and the viscosity of the food rope is removed by the action of gastric acid (the pH value of the existing gastric juice is generally 5-6), so that the food particles in the rope are free. At the same time, food is screened by the cilia in the screening area of the stomach, and fine food particles are sent to the digestive gland through the digestive gland tube at the upper end of the stomach. The digestive gland is the place where the cells digest and absorb food. Larger food particles are digested in the stomach. Undigested food enters the intestine through the folds of the stomach wall, is partially digested by the intestine, and finally forms fecal particles in the intestine. The anal orifice is located at the back end of the jacket cavity, and the formation of fecal particles reduces the pollution to the jacket cavity, and the fecal particles can be discharged out of the body with the water flow. Protomollusk's body cavity is located in the back middle of the body, surrounding the heart and part of the intestine, so it actually represents the pericardial cavity and visceral cavity. The heart includes a ventricle at the front end and a pair of auricles at the back end. Branches of arteries leading from the ventricles form small blood vessels, and finally enter the interstitial space to form blood sinuses, and then converge into veins, which return to auricles and ventricles through blood such as kidneys and gills. This is an open cycle. Blood contains deformed cells and respiratory pigments, and the main respiratory pigment is hemocyanin.

The excretory organ is the posterior kidney, which is located on both sides of the pericardial cavity. One end of the posterior kidney communicates with the pericardial cavity, which is called the internal renal orifice, and the other end communicates with the outside world, which is called the external renal orifice. The pericardial cavity receives the metabolites released by the heart and glands in the pericardial cavity, and enters the kidney from the renal orifice with the liquid in the pericardial cavity. The kidney has a certain reabsorption ability, it recovers useful salt, and useless waste becomes urine, which is excreted through the external hole and cavity of the kidney.

Schematic diagram of roller body

The nerve structure of protomollusk is very simple, forming a nerve ring around the esophagus, from which two pairs of nerve cords are separated, and a symmetrical foot cord on the ventral surface dominates the muscle contraction of the foot; The visceral cord with symmetrical back dominates the movement of viscera and coat. According to the speculation of existing mollusks, their sensory organs may also include a pair of eyes, a pair of statocyst located in the foot, and a pair of osphradia located on the lower branchial membrane, which are chemoreceptors.

The reproductive system includes a pair of gonads, which are located in the middle and posterior part of the anterior end of pericardial cavity. They are hermaphroditic and have no reproductive ducts. Sperm or eggs are released into the pericardial cavity when they mature. Because the gonad cavity is also a part of the body cavity, the germ cells are excreted through the pericardial cavity and then through the kidney. Fertilization takes place in seawater,

Schematic diagram of panel larvae

The embryonic development of protomollusks may be very similar to that of existing mollusks, and they also experience typical spiral cleavage, the formation of blastocyst holes, and the formation of gastrula embryos to form a wheel. The roller body is pear-shaped and has a typical primary roller, which surrounds the body in the upper part of the mouth. During cleavage, the first tetrad is located at the top, and there are ciliated bundles at the top. The roller exists not only in mollusks, but also in annelids.

The development of primitive species only goes through the wheel, and most of the existing mollusks have a short wheel-bearing period, and then enter the face-plate larva. Panel larvae have feet, shells, internal organs and other structures in their bodies. It is speculated that the protomollusk has no larval stage of panel, but it lost its pre-oral ciliary wheel from the trochanter, transformed into an adult and began to live in benthos.

Body division

edit

brief introduction

The body of mollusks can generally be divided into three parts: head, feet and visceral mass.

head

The front of the body. Agile species, head differentiation is obvious, with eyes, tentacles and other sensory organs, such as snails, snails, squid; Slow-moving species have underdeveloped heads, such as stone turtles; Cave-dwelling or settled species whose heads have disappeared, such as mussels and oysters.

foot

Usually located on the ventral side of the body, it is a moving organ. Because of the different lifestyles of animals, it often has different shapes. Some feet develop into leaves, axes or columns, which can crawl or dig mud; Some feet degenerate and lose their motor function, such as scallops; The types of fixed life, such as oysters, are not enough; Some feet have been specialized into wrists, born in the head, and are predatory organs, such as squid and octopus, which are called cephalopods; The side of a few kinds of feet (that is, fins) are specialized into sheets and can swim, which are called wings or fins, such as pteropods.

visceral mass

(visceral mass)

It is the part where the internal organs are located, usually on the back of the foot. Most kinds of internal organs, such as snails, are symmetrical, but some are twisted into spirals and lose their symmetry.

cerebral cortex

edit

(mantle)

It is formed by the skin folds on the back of the body extending downward, often wrapping the whole visceral mass. The cavity formed between the adventitia and the visceral mass is called the sleeve cavity. There are often openings such as gills, anus, renal foramen and implantation foramen in the coat cavity.

shell

The mantle consists of two layers of epithelium, the secretion of the outer layer can form shells, and the epithelial cells of the inner layer have cilia, which make water circulate in the mantle cavity, so as to complete breathing, excretion and ingestion. The left and right sheaths often heal in one or two places at the rear edge, forming an outlet hole (exhalation siphon) and an inlet hole (suction siphon). Some kinds of water inlet and outlet holes extend into pipes, which are called outlet pipes and inlet pipes.

shell

edit

(shell)

shell

Shelling in vitro is an important feature of mollusks, so the subject of studying mollusks is also called soft chemistry. Most mollusks have one or two or more shells of different shapes. Some are hat-shaped; Snails are spiral; Biped animals are tubular; Rod gills are petaloid. Some kinds of shells degenerate into inner shells, while others have no shells. Shells can protect software.

Shells are mainly composed of calcium carbonate and a small amount of shell matrix (conchiolin or conchiolin), which is secreted by epithelial cells of the mantle. Generally speaking, the structure of shells can be divided into three layers. The outermost layer is the stratum corneum, which is thin, transparent and shiny, and consists of shell matrix, which is not corroded by acid and alkali and can protect shells. The middle layer is ostracum, also known as prismatic layer.

pearl oyster

(primary layer) occupies most of the crust and consists of angular calcite. The innermost layer is the hypostracum of the shell, that is, the peral layer, which is full of luster and consists of phyllodes. The outer layer and middle layer are secreted by the edge of the mantle, which can gradually increase with the growth of animals, but not thicken; The inner layer is secreted by the whole mantle, which can increase its thickness with the growth of the individual. Pearls are formed by nacre. When the mantle is stimulated by the invasion of foreign bodies such as tiny sand grains, the epithelial cells in the stimulated area take the foreign bodies as the core and fall into the connective tissue between the epithelium of the mantle, and the trapped epithelial cells divide themselves to form pearl sacs, which secrete nacre and gradually form pearls layer by layer. According to historical records, more than 2200 BC, there was a record of freshwater pearl culture in China. Gong Yu). Pearl culture in Hepu, Guangxi has been famous since ancient times, and its picking began in Han Dynasty.

The growth of stratum corneum and prismatic layer is discontinuous. Because food, temperature and other factors affect the secretory function of the mantle, the growth rate of shells is different, so a growth line is formed on the surface of shells to indicate the growth rate.

digestive system

edit

The digestive tract of mollusks is developed, and a few parasitic species (Endostoma) are degraded. Most species have jaws and toothed tongues in their mouths, and one or a pair of jaws can help them hunt. Tooth tongue is a unique organ of mollusks. It is located on the surface of the tooth handle at the bottom of the mouth and consists of rows of horny teeth, which looks like a knife. When eating, the tongue moves back and forth, scraping food. The shape and number of small teeth on the tongue are different among different species, which is one of the important characteristics of species identification. Small teeth form horizontal rows, and multiple rows of small teeth form tongues. Each row has a central tooth, one or more pairs of left and right side teeth and one or more pairs of edge teeth. The arrangement of small teeth on the tongue is represented by teeth. For example, the teeth of China river snail (Cipangopaludina chinensis) are 2. 1. 1. 1.2.

circulatory system

edit

The secondary body cavity of mollusks is extremely degraded, leaving the pericardial cavity and the cavity of gonads and excretory organs. Protocoeloma exists in the gaps of tissues and organs, and blood flows in it, forming a blood sinus.

The circulatory system consists of heart, blood vessels, blood sinuses and blood. The heart is generally located in the heart cavity around the back of the visceral mass, and consists of the auricle and the ventricle. A ventricle, with thick wall, can beat and is the driving force of blood circulation; An auricle or a pair of auricles, usually corresponding to the number of gills. There is a valve between the atrial appendage and the ventricle to prevent blood from flowing back. Blood vessels differentiate into arteries and veins. Blood from the ventricle passes through the artery, enters all parts of the body, then flows into the blood sinus, and then returns to the auricle from the vein, so mollusks have an open tube cycle. Some fast swimming is closed-loop. Blood is colorless and contains amoeba-like cells. Some kinds of plasma contain hemoglobin or hemocyanin, so blood is red or cyan.

respiratory apparatus

edit

Aquatic species breathe through gills, which are formed by the extension of epithelial cells on the inner surface of the outer cavity. Gills have different shapes, and there are gill filaments on both sides of the gill axis, which are feathery and called shield gills. Only one side of gill axis has gill filaments, which are comb-shaped and called Chlamys farreri; Some gills are petal-shaped, called petaloid gills; Some kinds of gills are elongated into filaments. It is called a branch. Some primary gills disappear, secondary gills are produced on the back skin surface, and some species have no gills. Gills are paired or single, and the number varies, ranging from one or a pair to dozens of pairs. All species that live on land have no gills. Microvessels in a certain area inside the external cavity are densely packed to form lungs, which can directly absorb oxygen in the air. This is an adaptation to life on land.

Excretor

edit

mollusc

The excretory organ of mollusks is basically the posterior renal duct, the number of which is generally consistent with the number of gills, and only a few species of larvae are protorenal ducts. The posterior renal duct consists of glandular part and tubular part. The gland is rich in blood vessels, and the renal orifice has cilia, which opens in the pericardial cavity. The tubular part is a thin-walled tube with cilia on the inner wall, and the renal foramen is open to the external cavity. Posterior renal duct can exclude not only the metabolites in the heart, but also the metabolites in the blood. In addition, the pericardial glands and microvessels on the inner wall of pericardium are dense, which can eliminate the metabolites in pericardium and discharge them from the posterior renal duct.

nervous system

edit

The primitive nervous system has no differentiation of ganglia, only pharyngeal nerve ring, a pair of foot cords and a pair of lateral cords protruding backward. Higher species mainly have four pairs of ganglia, and there are neural connections between them. Cranial ganglion is located on the dorsal side of esophagus, which sends nerves to the head and front of the body to feel; The foot ganglion is located in the front of the foot, which extends the nerve to the foot to control movement and sensation. The anterior ganglion sends nerves to the mantle and gills. Visceral ganglion sends nerves to internal organs. These ganglia tend to concentrate, and some kinds of main ganglia gather together to form a cartilage-surrounded brain, such as cephalopods. Mollusks have differentiated sensory organs, such as antennae, eyes, osphradium and balance sacs, which are all sensitive.

Reproductive development

edit

Most mollusks are hermaphroditic, and many species are hermaphroditic; Some are hermaphroditic. Most cleavage forms are not at all.