Which consists of squid, octopus, cuttlefish, nudibranchs, snails, slugs, limpets, mussels, oysters, scallops, as well as many other lesser known animal species. According to scientists, there are more than 100,000 species of mollusks known to science today on Earth. This makes them second in species diversity after.
Mollusks have a soft body that consists of three main parts: the legs, the visceral mass and the mantle with the organ system. Many species also have a protective shell consisting of chitin, proteins and calcium carbonate. Mollusks are so diverse in shape that it is impossible to use representatives of one species to generalize the anatomical features of a group. Instead, science books often describe a hypothetical mollusk that has the characteristics of many species.
This hypothetical mollusk has a mantle, shell, leg, and visceral mass. The tunica is a layer of tissue enclosing the visceral mass. Many mollusks have glands that secrete a hard shell.
A leg is a muscular structure located at the bottom of an animal's body. The mollusk secretes mucus from the lower part of the leg to lubricate the underlying surface. Mucus facilitates movement, which is achieved by repeated contraction and stretching of the mollusk leg muscle.
The visceral mass is located above and below the mantle and includes the digestive system, heart and other internal organs. The circulatory system is open. Most species of molluscs use a single pair of gills for breathing, although some species have vestigial lungs, such as land slugs and snails.
Mollusks, unlike vertebrates, transport oxygen throughout the body using other molecules. They use hemocyanin (copper-based respiratory pigment), and vertebrates use hemoglobin (iron-based). Hemocyanin is less efficient at transporting oxygen than hemoglobin. For this reason, clams are more likely to move in quick bursts, but are not able to maintain movement for a long period of time, as they do.
Most marine molluscs begin life as larvae, which later develop into adults. Freshwater and land snails are formed in eggs and hatch miniature but fully formed as adults. Although molluscs are most common in marine habitats, they are also found in freshwater and terrestrial environments.
Molluscs are believed to have evolved from segmented, worm-like animals similar to modern flatworms. Their closest living relatives are annelids and flatworms.
Classification
Mollusks inhabiting the planet today are divided into the following classes:
- Pit-tailed (Caudofoveata);
- Sulcate-bellied (Solenogastres);
- Armored (Polyplacophora);
- Monoplacophorans (Monoplacophora);
- Bivalve (Bivalvia);
- Spadefoot (Scaphopoda);
- Gastropods (Gastropoda);
- Cephalopods (Cephalopoda).
Answer the questions: 1. Why did mollusks get their name? 1. How did mollusks get their name? 2.What mollusks live in our area? 2.What mollusks live in our area? 3.What is the significance of mollusks in nature and human life? 3.What is the significance of mollusks in nature and human life?
Type Mollusks Class Armored Class Sulcate-bellied Class Spadepods Class Bivalves Class Gastropods Class Monoplacophorans Class Cephalopods
Gastropods Nudibranch mollusk Grape snail Neptunia despecta Lambis isillipeda (species) Field slug
Bivalve Sea pearl mussel Tridacna major (250 kg) Gray's mussel Edible molluscs (species)
Blue-ringed octopus -Lives off the coast of Australia -Length up to 20 cm, weight up to 100 g -The bite is fatal, the poison causes paralysis of the respiratory muscles within 30 minutes Nutritious and tasty dishes from squid, scallops, mussels, hearts and coastal snails
Answer the questions: 1. Explain how mollusks are adapted to their habitat? 1.Explain how mollusks are adapted to their habitat? 2.What are the similarities and differences between gastropods and bivalves? 2.What are the similarities and differences between gastropods and bivalves? 3.List the ways to protect mollusks known to you from enemies. 3.List the ways to protect mollusks known to you from enemies. 4.What allows cephalopods to move quickly in water and escape from enemies? 4.What allows cephalopods to move quickly in water and escape from enemies?
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 inhabitants of the sea, 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) type of animals 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. shelled 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, a 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 of 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 the 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, the 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
Why are mollusks called that? Do they have teeth? How do these strange creatures even work? Our lesson will help you answer these questions for yourself.
The following concepts were introduced: malacology, mantle, mantle cavity, radula.
Topic: Animals. Shellfish
Mollusks do not have true segmentation. A leg is a muscular unpaired outgrowth of the abdominal wall of the body, usually used by mollusks for movement. The torso contains all the major internal organs. The mantle, a large fold of epithelium, extends from its base. It forms a mantle cavity connected with the external environment. This cavity contains the excretory tracts of the reproductive, digestive and excretory systems, the respiratory and chemical sense organs.
Mollusks are bilaterally symmetrical animals. However, again many of them partially lose this symmetry. The body of most species of mollusks is completely or partially covered sink. Sometimes it may be buried inside the body or absent. The shell consists of three layers: horn (outer), porcelain and mother-of-pearl (inner). The porcelain layer is the thickest, it is limestone. Many shells have bizarre shapes and vary in color and structure (Fig. 2).
Rice. 2. Murex shell ()
The shell substance is secreted by cells mantle. The ancestors of mollusks probably did not have shells, but only had calcareous needles on their covers. A similar structure of the integument is characteristic of some primitive modern mollusks. Chitons have a shell consisting of 8 plates.
Respiration in mollusks living in water is carried out gills, and in terrestrial ones - bag-shaped lungs. Air enters them, and blood vessels branch in the walls of the lungs. Some aquatic mollusks carry out gas exchange through the surface of the mantle. The circulatory system is usually open. It includes heart(a contractile organ that ensures the movement of blood through the vessels and cavities of the body) and vessels. The heart is made up of ventricle and one or two atria. Blood vessels drain blood into the body cavity. The blood then collects again in the vessels and enters the gills or lungs.
The digestive system is continuous. Consists of the mouth, pharynx, esophagus, stomach, intestines and anus. The structure of the digestive system varies greatly among mollusks of different classes, depending on the type of nutrition. In the oral cavity of mollusks there is a muscular tongue with chitinous teeth. These teeth form the so-called radula, or grater(Fig. 3). In herbivores, the grater is used to scrape off plant food; in carnivores, it helps to retain prey. From the pharynx, food passes through the esophagus into the stomach and intestines. Undigested food remains are expelled through the anus.
Substances by which food is digested are secreted digestive gland. Open into the oral cavity salivary glands. Excretory organs of mollusks - kidneys(two or one).
In primitive mollusks, the nervous system consists of a peripharyngeal ring and four nerve trunks. In most representatives, nerve nodes - ganglia - are formed. The suprapharyngeal nerve ganglion receives the greatest development; in the most developed representatives of the type, it can, without exaggeration, be called the brain. Mollusks have eyes. Different representatives of the type can have from 2 to 100 of them, they can have different structures (Fig. 4).
Rice. 4. Scallop eyes ()
Mollusks can be either hermaphrodite (snails) or dioecious (toothless). Mollusks reproduce by laying fertilized eggs. There are, however, viviparous ones. Development can be either direct (let me remind you, this is when a newborn individual looks like an adult) or indirect (with the presence of a special larval stage).
Bibliography
1. Akimushkin I.I. Animal world. Invertebrates. Fossil animals. - M.: “Thought”, 1992
2. Animal Life. T. 2. ⁄ Ed. Pasternak R.K. - M.: “Enlightenment”, 1988
3. Latyushin V.V., Shapkin V.A. Biology. Animals. 7th grade. - M.: Bustard, 2011
4. N. I. Sonin, V. B. Zakharov. Biology. Diversity of living organisms. Animals. 8th grade. - M.: Bustard, 2009
See English Wikipedia, learn zoology and English at the same time!
Homework
What shellfish live in your area? Where exactly do they live, what do they eat? Which ones have a shell and which ones don't? What do you think this might be connected with?
Read the paragraph on shellfish in your school textbook.
Loading...
