SHELLFISH

SHELLFISH, representatives of more than 80,000 species of INVERTEBRATE animals of the phylum Mollusca. These include the well-known snails, bivalves and squids, as well as many lesser-known species. Originally sea dwellers, mollusks are now found in the oceans, in fresh water and on land. The classes of mollusks include: primitive Gastropods, monovalves (slugs and snails), Bivalve mollusks, spadefoot mollusks and cephalopods (squids, etc.). The body of a mollusk consists of three parts: head, leg and torso. There is also a fold of skin attached to the body called mantle, producing a calcareous shell (shell), characteristic of most mollusks. The head is well developed only in snails and cephalopods, which have eyes, tentacles and a well-formed mouth. The torso contains the internal organs of circulation (blood vessels and heart), respiration (gills), excretion (kidney) and reproduction (gonads). Molluscs are usually dioecious, but there are many species that are hermaphrodites. Cephalopods, bivalves and gastropods are important fossils - evidence of the geological past. see also HERMAPHRODITES.

Shellfish. Remarkable experts in exploring new habitats, snails previously lived in the sea, but gradually some 22,000 species adapted to life on land, losing gills and developing air-breathing lungs. Most species of land snails, such as the vine snail Helix pomatia pictured here, are ground-dwelling and dull in color; there are a few arboreal species that tend to be brightly colored. Other species have returned to life in the water and must periodically surface to breathe.

Scientific and technical encyclopedic Dictionary .

See what "MOLLUSCS" is in other dictionaries:

Soft-bodied (Mollusca), a type of invertebrate animal. They presumably arose in the Precambrian; From the Lower Cambrian several are already known. classes M. They probably originated from small-segmented worm-like ancestors (annelids) or directly from flat... ... Biological encyclopedic dictionary

SHELLFISH- MOLLUSCS, or soft-bodied ones (Mollusca), are a well-closed type of invertebrate animals. The body is soft, undifferentiated, and typically bears a shell. The skin forms a fold of mantle that covers the body or grows together at the edges with its surface.… … Great Medical Encyclopedia

- (new Latin mollusca, from Latin mollis soft). Soft-bodied animals, slugs. Dictionary of foreign words included in the Russian language. Chudinov A.N., 1910. MOLLUSCS novolatinsk. mollusca, from dates. mollis, soft. Soft-bodied animals. Explanation... ... Dictionary of foreign words of the Russian language

- (from Latin molluscus soft) (soft-bodied) type of invertebrate animals. The body of most mollusks is covered with a shell. On the ventral side there is a muscular outgrowth of the leg (organ of movement). 2 subtypes: bokonervoe and testate; St. 130 thousand species. They live in... ... Big Encyclopedic Dictionary

Modern encyclopedia

Shellfish- MOLLUSCS, a type of invertebrate animal. The majority of the body is covered with a shell. The head has a mouth, tentacles and often eyes. The muscular outgrowth (leg) on ​​the ventral side is used for crawling or swimming. About 130 thousand species, in the seas (most), ... ... Illustrated Encyclopedic Dictionary

- (Mollusca) a type of animal with a solid, non-segmented body. Most representatives have a calcareous shell, whole or consisting of two, less often several separate parts. The organ of movement is the muscular unpaired... ... Geological encyclopedia

shellfish- the body of most animals is covered with a shell. ▼ side-nervous. armored: chiton tonicella. solenogastra: echinomenia. caudofoveates. shell monoplacophora: neopilina. Gastropods, snails, gastropods: prosobranchs: cowries. Littorina. abalone. trumpeters... Ideographic Dictionary of the Russian Language

shellfish- A type of soft-bodied, non-segmented invertebrate animals that usually secrete a substance to build a calcareous shell: snails, limpets, bivalves, chitons, squids. … … Technical Translator's Guide

- (Mollusca) (from Latin molluscus soft), soft-bodied, type of invertebrate animal. 7 classes: Gastropods, Monoplacophorans, Armored molluscs, Gross-bellied molluscs, Bivalve molluscs, Spadefoot molluscs and ... Great Soviet Encyclopedia

Books

• J.-L. Cuvier. Animal Kingdom. Molluscs, R. Aldonina. This publication introduces the reader to the section “Mollfishes” from the four-volume work of the French naturalist and naturalist Georges-Leopold Cuvier “The Animal Kingdom, Distributed According to...

Shellfish- bilaterally symmetrical or secondary asymmetrical three-layer animals. They live in marine and fresh water bodies, on land.

The body of most species of mollusks can be divided into three sections: head, trunk and leg. The head contains the mouth and sensory organs. The strongly thickened ventral side forms Various types legs The leg, as an organ of locomotion, can have a different shape: in swimming forms it turns into wide blades or tentacles, in crawling forms it turns into a flat sole.

The body is surrounded by a fold of skin - the mantle. Between the mantle and the body, a mantle cavity is formed, into which the openings of the digestive, excretory and reproductive systems open. The mantle cavity also contains respiratory organs and chemical sense organs (osphradia). All of the above is called the mantle complex of organs.

The muscles of mollusks are well developed and consist of muscle bundles. They are especially strongly developed in the animal’s leg.

The whole is reduced to the pericardial sac and the cavity in which the gonads are located. The space between the other organs is filled with parenchyma.

The digestive system is divided into three sections: anterior, middle and posterior. The anterior and posterior sections are of ectodermal origin, the middle section is of endodermal origin. In the pharynx of many species there is a specific organ for grinding food - the radula, or grater. The ducts of the salivary glands open into the pharynx, and the ducts of the liver open into the midgut.

The respiratory organs are represented by gills or lungs. Lungs are present not only in terrestrial species, but also in forms that have secondarily transferred to an aquatic lifestyle. Gills and lungs are modified sections of the mantle. In aquatic species, gas exchange can also occur through the skin.

The circulatory system is not closed: blood flows not only through blood vessels, but also through lacunae located in the space between organs. Mollusks have a heart consisting of two or more chambers. The heart is located in the pericardium (pericardium).

The excretory organs are the kidneys, which are modified metanephridia. The kidney begins as a funnel in the pericardial sac and opens with an excretory opening into the mantle cavity.

The nervous system of most mollusks is represented by several pairs of nerve ganglia, which are located in different parts of the body. This type of nervous system is called scattered-nodular. In addition to reflex activity nervous system performs the functions of regulating growth and reproduction by releasing various neurohormones. Mollusks have organs of chemical sense (osphradia), balance, and numerous tactile receptors are scattered in the skin. Many species have eyes.

The predominant number of species of mollusks are dioecious animals, but bisexual species are also found. Development in all terrestrial species, in most freshwater and some marine inhabitants is direct. If development proceeds with metamorphosis, then either a trochophore-type larva or a veliger (sailfish) larva emerges from the egg.

The phylum Mollusks are divided into classes: Gastropoda (Gastropoda), Bivalves (Bivalvia), Cephalopoda (Cephalopoda), etc.

The question of the origin of mollusks is still discussed by zoologists. Currently, the most proven hypothesis is the origin of mollusks from primary coelomic trochophore animals, from the same group from which annelids originated. The relationship of mollusks and annelids is evidenced by the similarity of embryogenesis (spiral fragmentation, metamerism of the rudiments of some organs, teloblastic anlage of the mesoderm) and the presence in lower mollusks of a trochophore larva, similar to the trochophore of polychaetes. It is assumed that the primary mollusks were bilaterally symmetrical animals with a low body, covered with a slightly convex shell, with a muscular flat leg and an almost distinct head. Two lines of evolutionary development extend from the primordial mollusks. The first line leads to the formation of bokonervny mollusks; this group is not considered in this manual. The second evolutionary line leads to the appearance of shell mollusks. Among shell mollusks, the most primitive are monoplacophorans. It is believed that bivalves, gastropods and cephalopods evolved from ancient monoplacophorans.

Description of classes, subclasses and orders of the Mollusc type:

• Class Gastropoda

• Class Cephalopods (Cephalopoda)

  • Subclass Coleoidae

Theory for preparation for block No. 4 of the Unified State Exam in biology: with system and diversity of the organic world.

Type Mollusca

Mollusks, or soft-bodied ones, are a type of three-layered animals that have a coelom (secondary body cavity). Symmetry is bilateral, but in many species, during ontogenesis, organs are displaced and animals become asymmetrical.

A distinctive feature of the type is the presence of a mantle, a fold of skin around the body. The space between the mantle and the body is called the mantle cavity. The outside of the mantle is covered with a calcareous shell, which in some species can protect the entire body, while in others it can be reduced to a small plate. The body of animals is divided into head, torso and leg.

More than 100,000 species of mollusks are known, sizes range from 1 mm to 10 m (Antarctic giant squid). These are mainly aquatic animals. Some species lead a terrestrial lifestyle, preferring damp places. There is no consensus on the origin of mollusks, most of Scientists believe that their ancestors are annelids.

Classification

The type is divided into two subtypes: side-nervous And conch shell. The latter include animals with a solid or bivalve shell, forming five classes. Only three of them are considered within the school curriculum: gastropods, elasmobranchs And cephalopods.

Class Gastropoda

All gastropods have a whole spirally twisted clockwise shell, asymmetrical body, separate head. The head contains eyes, tentacles, and a mouth. The leg is usually large, flattened below, forming a sole. There are many mucous glands on the sole, which helps the mollusk move on various surfaces.

Digestive system

In the digestive system Gastropods are divided into foregut, midgut and hindgut. The foregut includes the oral cavity, pharynx and esophagus. In the oral cavity there are powerful horny jaws. The pharynx has thick muscular walls and a muscular “tongue” on which rows of chitinous teeth are located. Such a device is called a radula, which translates as “scraper”. Using the radula as a grater, herbivorous mollusks rip off food particles from plants, and acting like a drill, predators bite into the covers of other animals.

The midgut consists of the stomach and several loops of small intestine. The hindgut opens into the mantle cavity with the anus near the head of the mollusk.

Respiratory system

Respiratory system form gills or, in the case of the pulmonary subclass, an unpaired lung. Gills can be of two types: primary and secondary. Primary gills (cnetidia) are retained into adulthood in a small number of species; they are cords with many feathery projections where gas exchange occurs. Based on the location of the cnetidia, the subclasses of prosobranchial and opisthobranchial gastropods are divided.

Secondary gills have nothing in common with true gills - they are simply abundantly supplied with blood protrusions on the body that serve for gas exchange.

The lung is present in terrestrial and freshwater gastropods and is a modified section of the mantle cavity. The surface area of ​​the lung increases significantly due to many folds.

Circulatory system

Circulatory system open type, consists of a heart and a developed vascular system. Between the afferent and afferent vessels there are not capillaries, but lacunae. From the lacunae, blood collects first into the venous sinuses, then into the veins.

Excretory, nervous and reproductive systems

Excretory system consists of two (in many species - one) buds. The kidney, a funnel with cilia, faces the pericardial cavity. Through it, metabolic products enter the mantle cavity.

Nervous system well developed, consists of large nodes (ganglia) and trunks between them. This type of nervous system is called scattered-nodular. On the head there are tactile tentacles, eyes, and olfactory labial tentacles. The nerves from them extend to the cerebral ganglion.

The organ of balance is statocysts - small bubbles with liquid lined with sensitive cells. The liquid contains hard pieces of calcium carbonate, which press on the walls of the statocyst if the mollusk tilts.

Reproductive system consists of an ovary or testis and reproductive ducts. Gastropods can be either dioecious or hermaphrodite. Cross fertilization, internal. The female lays eggs, from which a free-swimming larva emerges, the swallowtail.

Class Bivalves or Lamellibranchia (Bivalvia or Lamellibranchia)

This is a fairly large group of more than 20,000 species, the classic representative being the toothless one (Anodonta). Dimensions vary from 1 mm to 1.5-2 m. They live in fresh and sea water.

A distinctive feature of the structure is the absence of a head. The body consists of a leg and a torso, enclosed in a bivalve shell. The valves are connected by an elastic ligament, a ligament, which, at rest, keeps the shell open.

Powerful adductor muscles allow the mollusk to close its shell. Some species (for example, scallops) can move quickly using jet propulsion, opening and quickly closing the valves. However, most species lead an attached or sedentary lifestyle, moving slowly with the help of their legs.

The inside of the shell is covered with a layer of mother-of-pearl. After a foreign body enters the mantle or between the mantle and the shell, the glandular cells around it secrete nacre. With a successful combination of circumstances, a pearl is formed.

In bivalves, the edges of the mantle grow together, and tubular spaces—siphons—are formed between them. The toothless fish has two siphons; through the lower one, water enters the mantle cavity, and through the upper one it leaves the body.

Digestive system simplified, pharynx reduced. The stomach is voluminous; the liver ducts flow into it. The stomach is followed by the midgut, then the hindgut. The hindgut passes through the heart and opens into the mantle cavity at the anus.

Bivalves feed mainly by filtration, driving water through siphons. This helps clean up water bodies.

Breath gill. The structure of the gill apparatus is varied; in some species it is absent and respiration is carried out through the surface of the body.

Blood system open The heart is three-chambered, consisting of a ventricle and two atria. Primitive species retain two hearts.

Excretory system formed by the kidneys. Each kidney opens at one end into the pericardial sac, and at the other into the mantle cavity. There are also pericardial glands that remove waste products into the pericardial cavity.

Due to a sedentary lifestyle, nervous system poorly developed. Consists of three pairs of ganglia. Head tentacles and eyes are absent, but there may be numerous (up to 100!) ocelli scattered along the edge of the mantle. There are also statocysts, organs of touch and organs of chemical sense.

Sexual system The vast majority of bivalves are dioecious. Fertilization occurs in females in the mantle cavity, that is, in the external environment. Larvae emerge from the eggs. In marine mollusks, the larvae swim freely, then settle to the bottom and turn into adults.

Bivalves are powerful biofilters and play an important role in maintaining biological balance in water bodies. Some species (mussels, oysters) are considered delicacies. From others, mother-of-pearl or pearls are obtained (sea and river pearl mussels). Bivalve can cause significant damage by settling on hydraulic structures and clogging pipes. The shipworm, or hornworm, undermines wooden piles and boats.

Class Cephalopoda

The class includes about 700 species of mollusks. It includes numerous inhabitants of warm seas: octopuses, squids, cuttlefish, nautiluses.

One part of the leg has been modified into tentacles with suction cups that surround the mouth opening. Two longer tentacles are used to catch prey. The other part of the leg forms a funnel into which the mollusk sucks water. With a sharp expulsion of water, jet thrust is created and the animal moves.

Like all mollusks, cephalopods have a mantle. She is muscular and participates in the movement along with the funnel.

Cephalopods lead an active lifestyle. The shell disappeared in the process of evolution, but its remains may be found under the skin.

Digestive system well developed. All cephalopods are predators. They hunt using tentacles and poisonous salivary glands. In the pharynx there are powerful horny jaws that form a beak. With its help, the mollusk tears off pieces of food and grinds them.

The esophagus extends from the pharynx, which can form a goiter to store food. The stomach is large, with many folds, divided into two parts. The small intestine passes into the rectum, the anus opens on the abdominal side of the body.

The ink sac duct flows into the rectum - this unique gland produces a brown-black substance. When the clam is frightened, it releases an ink cloud and hides.

Breath carried out using cnetidia. The powerful muscles of the mantle ensure a constant flow of water through the gills.

Blood system almost closed, but the blood still flows not through the capillaries, but through the lacunae. The heart is three-chambered, like a bicuspid one. The increased blood flow near the gills is supported by contracting arteries - gill hearts. Blood in the air becomes blue color, as it contains hemocyanin.

excretory the system consists of 2 or 4 kidneys.

Nervous system much more perfect than other mollusks. Large cerebral ganglia merge into the brain. The esophagus passes through it, so large pieces of food can damage the brain.

The sense organs are well developed. Large eyes are originally skin outgrowths.

Reproductive system dioecious. Fertilization is internal, development is direct, without a larval stage. Caring for offspring is not typical.

Carp anglers, somyatniks, yazyatniks, breamers catch big fish for shellfish and especially good in the second half of summer and early autumn, using them both as bait and groundbait.

According to scientists, almost all fish would happily eat shellfish if it were not for the hard protective shell. But it’s easy for fishermen to remove the shell...

Shellfish nutrition

Mollusks have a varied diet: they can suck up bacterial film from various underwater surfaces, they can gnaw, they can grind detritus, they can simply filter organic suspensions... But they also participate in the food chain and are happily eaten by fish. The meat of these mollusks is very nutritious, it is rich in vitamins and proteins and can be eaten by almost any fish. Mollusks, like other creatures, live where there is more food and where it is quieter.

Where do mollusks live?

Shellfish They are very widespread in our reservoirs: they live in large and small lakes, rivers, ponds and streams, in standing and running water. There is probably no place where they do not live. Most of the mollusks are found on the shores with thickets of grass, where there are snags and all kinds of shelters. A large number of coils, bitinium, pearl barley can accumulate in places where wastewater is discharged, where organic matter coming out of the sewer settles to the bottom, which turns this bottom into a real table with “delicacy” products.

It turns out that shellfish from all over the area come to this place to feast to their heart's content. There are also fish hanging around there, eating these mollusks. According to scientists, the biomass of mollusks is much greater than the biomass of other benthic organisms taken together. And this is especially typical for our rivers. Under these conditions, mollusks develop very well, sometimes covering the bottom of the reservoir with a continuous carpet.

Types of shellfish

According to scientists, from 40 to 60 species of “shells” live in our reservoirs. Very small, and these peas and balls have a shell of only 5-10 mm.

The larger ones, and these are coils, bitinia, zebra mussels, have an even larger size. Toothless and pearl barley can grow up to 25 cm.

How do mollusks move?

“Snails”, “shells” - all these mollusks can move, that is, move, crawl both along the bottom and over aquatic vegetation. Bivalves have a very muscular leg (a sort of triangle of muscles), with the help of which they can move tens of meters, leaving a characteristic trail behind them - a path.

Who eats shellfish

Almost all fish eat the delicious meat of mollusks, with the exception of the podust - a perphyton-carrying fish, probably this water cow, and also the filter-feeding silver carp. Not every fish is able to reach this delicacy, since the mollusk has a strong armor - a “shell”. The strength of armor varies - some are thicker, some are thinner. The soft, thin shells of peas and balls can be chewed by many fish, especially carp, bream, silver bream, and crucian carp. In reservoirs where there is little grass and a lot of fish, there are very few such mollusks, since they are eaten by everyone who is not too lazy.

Coils and bithinias have an easier life: their shells are more massive and larger, and it is more difficult for most fish to crush them. Large specimens of ide, bream, and roach easily cope with them. Large whitefish are very fond of bithinia and can eat a couple of hundred shells within a day. The zebra mussel shell is very popular with the roach, which is the only one of its kind to eat them. Not every fish can crush the barley shell, which is toothless.

Catfish, large bream, carp - they eat these large mollusks, whose shells have not yet become strong. Adult toothless and barley fish are eaten only after they die, when the closing muscle no longer functions. In this case, the valves at the shell separate and the fish is able to suck out the soft and tasty contents.

Trout and eel feed on small shellfish. Fish such as tench happily eat all kinds of living creatures that are found in aquatic thickets. But due to the fact that its mouth is soft, it cannot crush a large shell, so it has to feed on young mollusks. Most of all, tench loves balls and reels.

Growing burbot and catfish eat mollusks often and with great pleasure. Having matured, they of course switch to feeding on fish, but they will not swim past a dead or crushed toothless fish whose shell is open.

Black carp, with pharyngeal teeth like millstones, is a real thunderstorm for shellfish. He is capable of crushing almost any shell, as long as it fits in his mouth. Well, a large carp can put anything into its mouth... Black carp can easily cope with zebra mussel - which has a powerful shell.

Shellfish are food for fish all year round, regardless of the season, but most of all in the fall. Fall shellfish are much tastier than spring or summer shellfish. But it's not that. It turns out that aquatic vegetation dies off and the shells have nowhere to hide, and accordingly it is easier for fish to detect them. Much depends on the feeding rhythm of each type of fish. If at this time of year the fish does not feed or feeds poorly, then it will not be happy with shellfish.

What are the diseases of shellfish?

Many have seen inky black spots ( diplostomiasis) on fish such as roach, bream... The intermediate hosts here are reels and fish, the final hosts are tree frogs and herons.

Tetracotylosis– here the causative agent of the disease must undergo development in a gastropod before infecting fish.

And it turns out that our fish shellfish bring both benefit and harm.

Classes of mollusks and their features

All representatives of this class have a soft, inarticulate body, a shell or its remains and a special fold of the skin - the mantle, which forms the mantle cavity.

Their mantle secretes substances from which the shell is formed (horny substances, lime and mother-of-pearl). Some mollusks have a head, muscular legs and a torso. Many of them have small eyes.

Octopus (lat. Octopus vulgaris) belongs to the cephalopods

Mollusks differ not only in size, but also in their anatomical structure and behavior. For example, about 80% of the species of these animals belong to the class of gastropods, about 19% are to the class of bivalves, and only about 1% are to the rest of the class of mollusks.

Scallops (lat. Pectinidae) belong to the family of marine bivalve mollusks

Classes of mollusks: gastropods

Gastropods (snails) are the largest class in the mollusk family (about 90 thousand species). This group includes grape snails, slugs, coils, and pond snails. Coils and pond snails live in small fresh water bodies, and slugs live in damp places on land (usually in vegetable gardens and fields), and grape snails only in vineyards.

Almost all snails eat plants, but sometimes they eat small insects. Among them there are predators, for example rapana (they live in the seas - they eat mussels and oysters).

Marine gastropods (lat. Gastropoda)

The structure of gastropods

Gastropods of the mollusk class have a single shell that looks like a small curl. And in some mollusks (for example, slugs), the shell is reduced or completely hidden under the skin itself. Like all representatives of this species, they have a leg, torso and head. On their head they have a mouth, eyes and two or one pair of tentacles. The muscular leg of mollusks occupies almost the entire abdominal part of the body.

In gastropods, the mantle looks like a pocket that forms a “lung” with breathing holes. Oxygen from the atmospheric air fills the “lung” and penetrates through the wall of the mantle directly into its branched blood vessels and carbon dioxide comes out from the blood vessel.

All gastropods scrape food using a so-called grater - a tongue that is covered with numerous denticles (horny teeth). They have salivary glands - from the ducts they flow directly into the foreguts; they have a digestive gland that combines the functions of the liver and pancreas.

Classes of mollusks: cephalopods

In addition, the order of cephalopods includes cuttlefish, squid, and octopuses (about 675 modern species). These mollusks inhabit mainly warm salty seas and feed on fish, crabs and other animals. Cuttlefish and squid actively pursue their own prey, and octopuses lie in wait for it.

Nautilus (lat. Nautilus pompilius) - a marine cephalopod that appeared 500 million years ago, is considered the only one among modern cephalopods with an external chamber shell

The structure of cephalopods

In addition, they can quickly change the color of their body, which in cephalopods consists of a head and torso. Most animals have a crown around their mouth, consisting of 8 arms (in cuttlefish and squids) and a pair of tentacles with large suckers. Tentacles and arms were formed from particles of legs. But the second part of the legs forms a funnel, which is connected to the mantle cavity itself.

The shells of cephalopods are internal, often reduced or completely absent. It is important to note that their mantle cavity functions similarly to a jet engine: through mantle slits, water is drawn directly into the mantle cavities, and then forcefully thrown out through the funnel itself. Cephalopods are crushed with fairly thick and powerful horny jaws, while others are crushed with a grater. They have two pairs of internal salivary glands.

Squid (lat. Teuthida) is another representative of the cephalopods

Origin of mollusks.

Many scientists are of the opinion that all mollusks descended from ancestors - worm-like marine organisms, or more precisely, from annelids. As evidence, they cite the similarity of the larvae of many gastropods of marine mollusks, as well as the larvae of polychaete marine worms. In addition, some primitive mollusks have a fairly close resemblance directly to the annelids themselves.

However, some scientists believe that mollusks originated from a genus of giant cephalopods living in Ordovician period, 470-440 million years ago (Cameroceras lat. Cameroceras) fossilized shells of which have been found in North America, South America and Spain.

Cameroceras (lat. Cameroceras) belongs to the genus of giant cephalopods orthocons

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The world of aquatic invertebrates is rich and diverse, and these articles will tell you about them: