molluscs

There are different species of shellfish depending on where they live - some live in salt water, such as the sea, and others live in fresh water, such as rivers and streams. The most famous Marine shellfish are the gray-black mussel, and the pearl clam is widely distributed in freshwater basins. The breeding season for shellfish is between spring and summer. Females lay their eggs in the water, and males, in turn, discharge their mature sperm stream into the water. Certain chemical signals between the two ensure simultaneous emission. Sperm and egg meet in water to be fertilized. Soon, the fertilized eggs hatch into small larvae. These larvae gradually develop into juveniles. After about four weeks, they grow out of their shells and fall to the bottom. They stay there, and gradually, like a ship throwing an anchor, they latch onto passing fish. These "anchors" are thin flagellates, which are also called "whiskers." ^[1] .

There are many varieties of shellfish, common are red shell, turbino shell, field snail, conch, clam, clam and so on ^[2] .

The body of shellfish is soft, symmetrical, without sections, by head, axe-foot , Splanchnic sac , mantle and Sea shell Consists of 5 parts. The head has sensory organs such as mouth, eyes and antennae. The axe foot is located on the abdomen of the body and is composed of strong muscles. It is an organ for crawling, digging through sand or swimming. The visceral sac is located on the back of the body and includes heart Kidneys, stomach, intestines, Digestive gland and gonad And other internal organs. The outer layer of the body is covered by the outer layer of the outer layer of the epidermis and the connective tissue and a little muscle between them. mantle Epidermal cell The secretory shell, mantle and shell are all protective organs of shellfish.

The nervous system of shellfish is composed of four pairs of ganglia of brain, foot, side and viscera and the nerves connected with them. Cranial nerve It is located on the dorsal side of the esophagus and sends nerves to the head and anterior part of the body. Foot ganglion Located in the front of the foot, sending nerves to the foot; Lateral ganglion Located at the front of the body, sending nerves to the coat and gills; The visceral ganglion is located at the back of the body and sends nerves to the internal organs. The primitive species of shellfish has a simple nervous system and no significant ganglia, and the more evolved species form ganglia, and the more evolved species are concentrated in the head to form a "brain". Sensory organ There are mainly antennae, eyes, statocyst , olfactoscope Let's wait.

The digestive system includes the mouth, lingual esophagus, Stomach and intestine , anal and accessory Digestive gland Among them, the tongue is a special organ for licking and grinding food of shellfish, and it is also one of the important bases for classification.

shellfish gill And lung breathing. The aquatic species have gills, usually formed by the extension of the skin on the inner surface of the mantle, called protogills. Each branchial lamella has gill filaments on either side or on one side of the gill axis, and cilia are produced on the gills. The movement of the cilia causes the flow of respiratory water to follow a certain route through the gills Gas exchange . In some species, the gills disappear and breathe by using the skin surface or by forming secondary gills on the skin surface (metabranchia). Part of the mantle of terrestrial species forms lung chambers with a dense network of veins through which they breathe in the air.

Circulatory systems are generally open-tube, but in higher cephalopoda The arterial and vasculature are connected by microvessels and become closed. The center of the shellfish circulatory system is the heart, which has 1 ventricle, 1, 2 or 4 auriculae. Blood contains hemocyanin, generally colorless, only a few species such as bivalve arca gastropods the Planoborus It has heme. The blood is red.

The main organ of the excretory system is the kidney. Kidney container cilium the nephridium Form, end with Pericardial cavity The other end opens in the coat cavity. The number of kidneys varies by species, with 6 pairs, 2 pairs, 1 pair, or only 1 pair. In addition to the kidneys, some types of glands surrounding the wall of the heart cavity or a part of the liver also have excretory functions.

The reproductive system includes the gonad, the genital duct, the conjunctivium and some accessory glands. hermaphrodite or hermaphrodite .

The lifestyle of shellfish varies from species to species. The terrestrial species are gastropods, which use their muscular feet to crawl on land.

Aquatic species have planktonic, swimming, crawling, sessile, perforated and parasitic lifestyles. Planktonic species are all floating in the water with the current. Generally, the individuals are small, shells are thin or no shells, and some species have specialized fins, such as Pteropoda and Heteropoda. Some species can secrete enough of one Buoyancy sac It carries animals floating on the surface of the ocean, such as the sea Snail ( Janthina ). Swimming living species can migrate long distances in the ocean, such as cephalopod cuttlefish, squid , Malabar ( Ommastrephes ) and so on, their full specialization into wrist and funnel , trunk There are fins on both sides, and the water spray and the swing of the fins can swim quickly and smoothly. Some bivalves such as scallop Chlamys farreri Chlamys ), Sun-moon shell ( Amussium ), file clam ( Lima Although they are not swimming life species, but when necessary, they can use the sharp opening and closing of the shell and the role of the tentacles of the outer membrane to swim in the sea. Most aquatic shellfish live benthically, or crawl on the bottom, or dig holes in the bottom, or live attached to other foreign objects. Such as jade snail, mud snail ( Bullacta Wait to crawl on the bottom of the sand, Bao, Horseshoe shell ( Trochus ), newshell ( Turbo Wait to crawl on the rocks, some nudibranch Such as manatee ( Doris ), carrot snails living in fresh water ( Radix ), Planoborus ( Planorbis (and so on Aquatic plant Crawl up. Their foot muscles are particularly developed, plantar surface is wide, suitable for crawling. Many benthic shellfish live entombally, and most bivalves belong to this type. Their muscular, axe-edged feet are designed to dig through the mud and sand and bury their bodies underneath, like the clams. Venus ), cherry clam ( Tellina ), solen ( Solen ), the sea beetle ( Mya (Wait, they're developed Inlet pipe And the outlet pipe communicates with the bottom surface for feeding and breathing. Some benthic shellfish camps live attached, like mussel Scallops, unequal clams ( Anomia ), etc., the feet can secrete byssus To attach to rocks, Coral reef Live on other shells or objects. oyster , pithecocephalus ( Chama ), Sea Daisy ( Spondylus ) and so on to one Fan shell These species generally do not move after fixation. Some benthic shellfish live on rocks, coral reefs, shells, bamboo and other foreign objects, also known as perforated organisms, such as lithophaga ( Lithophaga ), Pholatidae ( Pholadidae Some species, the drill clam ( Saxicava ), Shipworm ( Teredo ), Matt Sea bamboo shoots ( Martesia ), wood eating sea bamboo shoots ( Xylo-phaga Etc., all rely on developed water pipes and outside the tunnel to draw seawater for breathing and intake of water microorganism And organic debris as food. There are also parasites in shellfish. ectoparasitism helicoid Stilifer ), parasitic in echinoderm carpal Ambulacral groove Medium; endoparasitism endoshell Entovalva ) Parasitize the anchor Sea cucumber Inside the esophagus.

The way shellfish reproduce also varies from species to species. Monoplacophora , polyplacophora , Scaphopoda , Cephalopoda And the vast majority of probranchians are gynandrogynous, metabranchians, aplacophora , probranchia and bivalve A small percentage of the lungs and all of them snails All are hermaphrodite . There are also some species that have sexual changes, such as certain species oyster , shipworm and Sail shell ( Calyptraea ), etc. Both male and female species are fertilized either by mating or by releasing the sperm and eggs in water or in the gill cavity or "uterus" of the mother. Hermaphrodite species In which two individuals fertilize each other, some species have many individuals mating in a row, the first individual acting only as a female, the last individual acting only as a male, and the intermediate individual acting as both a female and a male, such as acanthus ( Acera ), aplysia ( Aplysia ), etc. Some eggs are scattered into pellets, others ovum Enclosed in the egg sheath, many of the egg sheaths stick together to form a group of eggs. Egg group shape, structure varies by species, such as natica ( Natica The eggs are bonded to the sediment into a collar, whelk ( Rapana The ootheca is petal-shaped and joined together like a flower chrysanthemum ; The eggs of the sea hare are vermicelli shaped, commonly known as Sea starch . Each of the squid eggs is wrapped in a round capsule, connected together much like a bunch of grapes. The number of eggs laid by shellfish varies greatly depending on how well it is protected during fertilization and hatching, and some species that produce their eggs in water for fertilization and hatching have particularly high egg production, such as the egg-laying American oyster. Crassostrea virgnica Spawn tens of millions to more than 100 million. Young type of eating oyster ( Ostrea edulis Only a few hundred thousand to a million capsules are produced. Calliope Nucula Capable of protecting the egg in a shell attached to it chitin In the sac, only 20 to 70 eggs are laid. Protogastropods The eggs are laid directly in the sea water for fertilization, the number of eggs is large, such as abalone can produce more than 100,000, and the eggs are produced in the "uterus" for fertilization and hatching species such as snail. Viviparus ) Only dozens of grains are produced, River snail ( Margarya ) only three to five are produced. Some species of shellfish reach their first anniversary Sexual maturity Life span is only 1 year, such as nudibranch And some species of cephalopods. Some species live longer, but most reach sexual maturity in 1 year. The rate of growth varies with species and environmental conditions. When the temperature is suitable and the food is sufficient, the growth is fast, and the growth is slow. The life span of shellfish is highest in bivalves, mussels and mussels Sea beetle ( Mya arenaria ) Can live 10 years, The mare's mother ( Pinctadamartensi ) can live for 12 years, clam Class has a longer life span, Pearl mussel ( Margari-tana margaritifera Can live for 80 years, Giant clam ( Tridacna They can even live for a century.

Feeding methods of shellfish include predation and filter feeding. Predatory species can be divided into herbivorous and carnivorous species. Many primitive gastropods are like abalone, Horseshoe shell , Cockle shell And many lungs snails For example spondylium ( Lymnaea ), Snail Phaedusa fumigata Clausilia All are herbivorous. Mesogastopoda Some of the species with water pipes, such as the phoenix snail ( Strombus ) and Neogastopoda Most of the species are carnivorous, either feeding on dead animals or eating them polyp Ring worms, bivalves, crab , fish and other food. Cephalopods are also carnivorous, hunting bivalves, crabs, and even chasing schools of fish. The vast majority of bivalves are filter feeders.

It is found mainly in the ocean, with a small number of species living in freshwater lakes.

Digestion: In the original sedimentary feeding species, the digestion of food and the structure of the digestive tract still retain the form and function of the original mollusk. For example, the stomach wall of protobranchia is very thin, which still retains the structure of stomach ladder and crystalline rod, and food is digested extracellular in the stomach, and intracellular digestion and absorption in the digestive sac. In higher filtered feeding species, there are no tentacles around the digestive orifice. The gastric shield and screening area in the stomach wall are underdeveloped, while the crystalline rod sac is developed and protrudes outside the stomach wall. In the capsule, the mucous secretions are solidified to form crystal rods, on which digestive enzymes (amylase, lipase) are adsorbed. Cilia in the capsule wall make the crystal rods rotate continuously, and the top of the crystal rods are dissolved and released for extracellular digestion. The rotation of the crystal rods also plays the role of mixing food and enzymes. The top of the rod is constantly worn by food, and the back end can be constantly replenished. The rotation of the rod also allows tiny food particles to enter the gastric blind sac for intracellular digestion and absorption. Indigestible food debris is discharged to the body through the intestines, anus, and water outlet holes. A slow but continuous flow of food through the digestive tract is characteristic of lambranchial filter feeders. Septobranchia are carnivorous animals, their muscular stomach wall is surrounded by chitin, forming a grinding stomach, its crystalline rod is not developed, into a small stick into the stomach, with more developed digestive enzymes.

Circulation and gas exchange: Bivalves have open circulation, and the pericardial cavity is located at the back of the body. There is a ventricle and two auriculus in the pericardial cavity, and there is a valve between the ventricle and the auriculus to prevent blood reflux. In protobranchias and filambranchias, the anterior great artery is only discharged forward from the ventricle, as in mussels; in lamellibranchias, the posterior great artery is also discharged backward from the ventricle, as in mussels. After flowing out of the artery, the blood branches to the front end of the body, feet and internal organs, etc., and forms blood sinuses in the tissues. After the blood sinuses, it gathers into blood vessels, passes through the kidneys and gills, and then flows back to the heart ear and ventricle. The gills are their main gas exchange site, and when water passes by, less oxygen is taken up by the gills than other mollusks, which may be related to the larger surface area of the gills than other mollusks. In addition, all bivalves have a more or less developed mantle circulation, in which blood flows out of the arteries and directly into the mantle to form blood sinuses, which collect into blood vessels or flow directly back to the auricle, or through the kidneys to expel metabolites and then flow back to the auricle. The jacket cycle is also an auxiliary site for gas exchange. It's not found in the blood of most bivalves Respiratory pigment Only a very small number of species, such as cockles and Lima, have heme, which makes tissues such as the mantle appear red. Septobranchiate gills have disappeared, and gas exchange is carried out entirely by the mantle.

Excretion: The excretion system of bivalves is a pair of metanephres located on the ventral surface of the pericardial cavity. The kidney is a long tube, but the inner renal opening is at the front of the pericardial cavity, and the outer renal opening is below the inner renal opening in the outflow stream, so the back end of the kidney is folded back, and there are glands in the first half of the kidney called glandular part, where the waste is filtered, followed by the bladder part, which is the storage place of metabolites. The probranchial kidney does not have the distinction between the glandular part and the bladder part. The kidneys of freshwater species reabsorb salt, so the excreted urine is hypotonic.

Nerves and senses: The nervous system of bivalves is relatively simple, the original species has brain, lateral, foot, and four pairs of ganglia, and the more evolved species, brain, and lateral ganglia are combined, so there are only three pairs of ganglia, the lateral ganglia is located on both sides of the esophagus, it controls the anterior adductor muscle and coordinates the movement of the foot and shell. The visceral ganglion is located on the posterior obturator muscle column, which controls the contraction of the visceral and posterior obturator muscles. The foot ganglion is located in the front foot muscle, which controls the movement of the foot. In addition, there are two pairs of nerve cords between the lateral and visceral ganglion, and between the lateral and the cerebral and the foot ganglion. The sense is not developed, in some species with large activity, such as scallops, there are pairs of small tentacles on the middle fold of the mantle edge, which contains tactile and chemical sensory cells, and many eyes, the structure of the eyes is more developed, and even contains crystals and omentum, which can feel the change of light intensity. In addition, there are a pair of balance sacs around the foot ganglia, which control the balance of the body. Many species have sensory epithelium, called olfactory detectors, under the posterior cleistor muscle or around the water outlet, that sense changes in water quality and flow.

Most species of shellfish do edible The meat of many shellfish is tender, delicious and nutritious. Cephalopod squid, squid, Malabar , octopus ( Octopus ) and other Marine creatures, abalone in the gastropod, phoenix snail, whelk ( Neptunea ), Oriental snail ( Babylonia ), volute ( Voluta ), whelk And many terrestrial ones Snail Etc are fishing objects, Bao, etc., or breeding objects. Many species of bivalves such as Glycylaridae ( Arcidae ), Scallopidae ( Pectinidae ), Mytilidae ( Mytilidae ), petalidae ( Pteriidae ), Ostreidae ( Ostreidae ), clam Family ( Mactridae ), Veneridae ( Veneridae ), Unionidae ( Unionidae ), Solen ( Solenidae Many species of the family are rich in resources, has developed into an important object of mariculture, the yield is also very considerable, in addition to fresh food, but also can be dried, pickled or canned, products are mussels (dried mussels), scallop scallop Adductor muscle ), dried oyster (dried oysters), dried razor clams, dried clams, Dried cuttlefish Squid eggs (the squid's nidles) and various canned shellfish. Many shellfish are indispensable to the fine Chinese medicine, such as Pearl and Nacre powder Bao's shell cassia The baby's shell, the squid's inner shell of the sea bladder, Snail meat The egg group of sea hare, etc. Small shellfish with large yields can be used as farm fertilizer and feed for poultry and livestock. The main component of the shell is calcium carbonate, is the raw material of firing lime, but also can make paint mixing agent, shell carving and other arts and crafts, and pearl is a valuable decoration.

But shellfish also do some harm to humans. Some shellfish are poisonous and can be poisoned by human consumption or contact. Some freshwater and terrestrial gastropods are parasites of humans and domestic animals Intermediate host For example Schistosoma japonica The larva parasitica oncomelania Inside me. Shipworms in the ocean, Sea bamboo shoot It is a kind of cave dwelling specialized in piercing wood or rock, which is very harmful to wooden boats, wooden piles and wooden and stone buildings in the harbor.

In order to avoid the safety hazards of shellfish as far as possible and enjoy delicious food, it is necessary to start from several aspects such as cleaning and cooking:

First, no guts. Pollutants such as heavy metals are easily enriched in the visceral mass of shellfish, while the content of heavy metals in muscle is the lowest. Therefore, only the muscle parts of shellfish can be eaten. "Look at the color" is an easier way to judge. After opening the shell, the slightly blackened meat is mostly internal organs. Some shellfish, which have a black line of sand inside, are also inedible.

Second, pick one with a smooth shell . Lumpy relative to outer appearance Fresh oyster , scallop Wait, Razor clam , mussel The appearance is clean and smooth, the attachment is less dirty, and the corresponding pollution is less.

Third, brine soak and fully heat . Before cooking, the shellfish should be put into salt water for a period of time. This helps the shellfish expel toxins and sand. Then, use a small brush to carefully clean the surface of the shell. Cooking methods preferred steaming, boiling, etc., can thoroughly heat, kill bacteria. When processing, it is necessary to put cold water into the pot to ensure the consistency of raw and cooked inside and outside. The method of barbecue is easy to cause uneven heating, outside cooking and raw, it is recommended to use less.

Shellfish money

Natural seashell

In the 21st century BC - the 2nd century BC, it was mainly used in the Central Plains, and gradually replaced by metal currency, the unit is "friend", and each picked up coin is "one friend". In the pre-Qin period, shell had the dual functions of coin and ornament. China's minority areas until the late Ming and early Qing Dynasty also used bei as currency, called "ba (left and right structure, left is' bei ', right is' ba ')".

Natural seashell

The 11th century BC, produced on the seashore, because of its strong and beautiful, it can be carried, and can count, and gradually evolved into Physical money .

Artificial shellfish (stone shell)

During the Shang and Zhou Dynasties of the 16th century BC - the 2nd century BC, the commodity economy continued to develop, and the demand for money continued to increase. In order to make up for the lack of natural currency circulation, imitation jade shell, bone shell, Tao shell, stone shell, etc., were collectively referred to as artificial Shellfish money . Their shape is similar to that of natural seashells, and their exchange value is about equal to or slightly lower than that of natural seashells.

Artificial shellfish (bone shell)

16th century BC - 2nd century BC

Artificial shellfish (jade shell)

16th century BC - 2nd century BC

Artificial shellfish (Tautosa)

16th century BC - 2nd century BC

Copper shell

11th century BC

Bao Jinbei

In the 11th century BC, in the middle and late Shang Dynasty, with the development of society, human beings mastered smelting technology, and metal shellfish currency appeared. It's shaped like a natural seashell. There are Kimbe Silver shell, copper shell, etc. The uncultured copper shell cast in bronze is the earliest to appear in China Metal coinage .

In October 2023, the latest version of the list of precautions for train passengers was released, and shellfish were carried on board, but they were required to be sealed and not eaten in the car. ^[3]