Shell reduction
Shell reduction is observed in almost all classes of mollusks.
So, in some shell plates sink deep into the body and lose their upper layers: the periostracum and tegmentum.
Also, immersion and reduction of the shell are characteristic of higher mollusks -. And if the inner shell carries a functional load (it is used to regulate buoyancy), then in and it is extremely rudimentary.
Among mollusks, an independent reduction of the shell is observed in different groups: firstly, in lung mollusks - among slugs (families , etc.) and, secondly, among - in suborders , etc.
Interesting Facts
So, protection - this is the function of the shell in mollusks. It would seem that there are no other answers to this question. However, Japanese scientists managed to discover in some species of gastropods the so-called ability for active self-defense. It manifests itself, in particular, in species such as Karaftohelix selskii and Karaftohelix gainesi. They have large shell sizes and a wider entrance to the "house".
When attacked, for example, by a beetle, the snail can turn its “house” almost 180 °, tilt it almost horizontally, defending itself and repelling the attacker. Of course, the muscles of snails with this ability are more developed than those of their relatives. Moreover, this ability did not appear in related species, as their feature, but was evolutionarily fixed in various habitats.
We hope you have received a fairly complete answer to the question of what function the shell performs in mollusks.
Structure
Inside the bivalve shell is placed the body of the mollusk, consisting of the body and legs. The leg is a muscular part of the body, with the help of which the mollusks move along the bottom or burrow into the ground. It often has a wedge-shaped shape and is able to protrude from the shell.
Inside the shell is the body of the mollusk
Many species, such as the mussel (Mytilus), have a byssal gland in the leg that secretes a substance that helps the mollusk attach itself to stones and similar substrates. Byssus is a strong thread. Some adult mollusks do not have such a gland, in which case it was most likely developed at the larval stage.
Shells of laminabranchs can have various sizes and shapes. The smallest deep-sea mollusks do not grow more than 0.5 mm in length. But there are also giants, for example, tridacna - an inhabitant of coral reefs in tropical seas. The size of this type of bivalve can reach 1.4 m in length with a body weight of up to 200 kg.
Most species have an oblong body flattened laterally. But there are also species with an elongated worm-like or almost spherical shape. The sink can be symmetrical or have valves of different sizes. Most representatives of bivalves have a lock on the shell valves, which prevents the valves from moving relative to each other.
Regardless of the shape and size, the shell consists of three layers:
- external - conchiolin;
- internal - lime;
- lower - mother-of-pearl.
The sea shell of a bivalve mollusk is thicker than that of a freshwater inhabitant
- Appearance
Let's look at the structure of bivalves. The folds of skin around the perimeter of the shell are called the mantle. If an aquatic inhabitant has the habit of burrowing into the sand, then this organ forms two tubes - the inlet and outlet channels. Then all interaction with the environment occurs through them. According to the first, oxygen and food enter the body, according to the second, the remains of vital activity are removed. The mantle cavity also includes the leg, horn openings and respiratory organs.
Respiratory and nervous systems of bivalve mollusks: these creatures are able to touch with the help of tentacles. They grow on the edge of the mantle. Through the latter, mollusks that do not have gills are able to receive oxygen. Gills in the form of two petals are located on both sides of the leg.
By the way, not everyone has it, if the bivalve leads a sedentary lifestyle, he does not need motive power (oysters, for example). And if the goal of the mollusk is to attach to a certain object for a long time, then a special gland located in the leg secretes special. threads with which the shell of a bivalve mollusk is securely attached where it needs to be.
As for the eyes, most of the species on our list do not have them. But, nevertheless, there are some representatives endowed with organs of vision. True, light-sensitive cells, which everyone has, help mollusks to navigate where the light is and where the darkness is.
- Internal structure
The soft-bodied have no bones. It should be noted that the circulatory system of bivalve mollusks is open, the blood circulates not only in the vessels, but also washes the organs of bivalve mollusks. The gut passes through the heart of these creatures. A pair of kidneys allows them to excrete metabolic products. Animals perceive odors poorly, their olfactory organs are underdeveloped. There are male and female individuals. However, cases of sex change in the middle of the life cycle have been recorded.
Definition of the word Sink by TSB
The shell is an external protective skeletal formation that covers the body of many invertebrates. Usually R. does not adhere tightly to the body and has an opening through which the animal can partially protrude outward. R. consists of organic substances, often with an admixture of calcium carbonate or encrusted with grains of sand, diatom shells, sponge needles, etc. R. are characteristic of some protozoa, most mollusks, as well as some arthropods and brachiopods. The shell of testate amoebas consists of a chitin-like or gelatinous substance and is often reinforced with grains of sand and other particles previously swallowed by the amoeba. The r. of most armored flagellates is formed by several plates of fiber. R. foraminifera is often impregnated with carbonic lime, sometimes encrusted with grains of sand, and rarely formed only by organic matter. It can be single or multi-chamber. The sizes of R. foraminifera range from 50 microns to several cm. The R. of mollusks is distinguished by a special skin fold - the mantle - and usually consists of 3 layers. prisms of aragonite, or calcareous spar, connected by conchin at an angle to the surface of the river. the middle layer (hypostracum, or mother-of-pearl) consists of aragonite plates layered on top of each other, also soldered by conchin. R. mollusks are very diverse in size and shape (in the marine bivalve mollusk tridacna R. weighs up to 25 kg and reaches a length of 1.7 m). in gastropods, it looks like a conical tube, usually coiled. in bivalves - R. of 2 valves connected on the dorsal side with each other by an elastic band (ligament) and a lock. In some cephalopods, the R. are spirally twisted and consist of many chambers (ship, fossil ammonites). In some modern cephalopods, the R. is internal, because lies under the skin of the back (cuttlefish, squid). In octopuses, as in some representatives of other classes of mollusks, R. is reduced. The R. of brachiopods consists of two valves—the dorsal and ventral valves (and not the right and left ones, as in mollusks), the R. of barnacles consists of two lateral valves, and in barnacles it has a truncated conical shape and is formed by several scutes secreted by the mantle. Incisors, scrapers, hoes, fishhooks, musical instruments, and various ornaments were made from molluscs. R.they were also used as vessels, and in some countries they served as money (for example, R. Kauri) and amulets. Mother-of-pearl is mined from pearl, which is used for the production of buttons, inlays, and so on. P. accumulations formed many sedimentary rocks, for example, fusunic and nummulite limestones are composed of P. protozoa, and shell limestone and pteropod silt are made of P. mollusks. V. Ivanov. Insert to the article Sink
Other interesting questions and answers
What are the moral problems of death? What is meant by the words "right to die"?
Guest2
The problem of death as such does not exist. There is a transition to the Subtle World. Only the Creator has the right to die. All living beings, spiritual souls have the right to life, which we receive by the grace of the Creator, the Heavenly Father.
Guest4
What is a mollusk shell? What are its functions and structure?
Aleksandr4
Shell - The skeleton of marine animals, which protects them from other animals.
The sink consists of several parts, more precisely of three parts.
- Peristracum - This layer is the uppermost layer (outer) which consists only of a protein - concholine.
- Ostracum - The second layer (middle) which consists of calcium carbonate - CaCO3)
- Hypostracum - The word Hypo means less, and Hypostracum means the bottom layer. This layer consists of sheets of calcium carbonate.
The shape of the shells is very diverse and does not repeat for every marine “Inhabitant” that has a Shell.
Shells for marine animals have a protective function. For us people, the sink has a different function - for aquariums, for the hall (it looks very nice on the shelf, and so on.
After the mollusks die, their shell helps many animals to hide, for example, crabs, after they find the mollusk shell, they take the shell as a mobile home.
Lilka-g5
What are the moral problems of death? What is meant by the words "right to die"?
Guest5
The problem of death as such does not exist. There is a transition to the Subtle World. Only the Creator has the right to die. All living beings, spiritual souls have the right to life, which we receive by the grace of the Creator, the Heavenly Father.
Guest6
What is a mollusk shell? What are its functions and structure?
Aleksandr4
Shell - The skeleton of marine animals, which protects them from other animals.
The sink consists of several parts, more precisely of three parts.
- Peristracum - This layer is the uppermost layer (outer) which consists only of a protein - concholine.
- Ostracum - The second layer (middle) which consists of calcium carbonate - CaCO3)
- Hypostracum - The word Hypo means less, and Hypostracum means the bottom layer. This layer consists of sheets of calcium carbonate.
The shape of the shells is very diverse and does not repeat for every marine “Inhabitant” that has a Shell.
Shells for marine animals have a protective function. For us people, the sink has a different function - for aquariums, for the hall (it looks very nice on the shelf, and so on.
After the mollusks die, their shell helps many animals to hide, for example, crabs, after they find the mollusk shell, they take the shell as a mobile home.
Lilka-g5
Sergey Kuksinsky13
How does an anchor hold a ship in one place?
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Due to the so-called. the holding force of the anchor and the elasticity of the anchor rope (chain). This is a whole science that is taught in maritime educational institutions.
There are a great many anchors and it is important to choose the optimal anchor for a particular watercraft. Anchors are held not only by ships, but also by various offshore structures: platforms, floating lighthouses, buoys, floating berths, landing stages, pontoons, breakwaters, etc.
I am engaged in the construction of yacht harbors (marines) and the Mitchell screw anchor has become a discovery for me relatively recently (there was such a wonderful British engineer Alexander Mitchell, he invented this anchor in the 19th century, by the way).
The screw anchor is screwed into the bottom and has a holding force of 10-15 times more than conventional anchors. With a very small weight, size and price. For me it's a personal anchor revolution
Andrey Mantula306
Similarities between rapana and toothless shells?
Larisa S.5
The shells of toothless and rapana have a completely different shape, it is easier to list the differences
And the only similarity is the structure. Both of them consist of a horn, porcelain and mother-of-pearl layer.
Elina Z.1
How are shells formed?
Guest3
A shell (shell) is the outer skeleton of mollusks, their fortress, which they themselves build throughout their lives. The mollusk grows, and its outer protection, the shell, also grows. Layer upon layer, the marine inhabitants fold the edges of their mantle, forming limestone crystals from the salts of sea water. In winter, mollusks grow more slowly than in summer, because of this, seams and convex growth rings form on the shell. From them, as from annual rings on a cut of a tree, you can calculate the age of a mollusk.
Svetlana Zh.3
Mollusk shells and man
Making buttons from bivalve shells
Use of sinks
Mollusk shells were used as material for the manufacture of various tools: fish hooks, chisels, scrapers, hoe attachments. The shells themselves were used as vessels, as well as decorations.
Extracted from shells, it is used to make various products, for example, as well as for.
In some areas, shells served - for example, on the islands.
Shells in art
Large shells were often depicted in their paintings by artists. An example is paintings that describe a mythological plot - birth. In the famous painting, Venus is depicted standing on a huge shell of a scallop, which was her symbol (see).
In a painting by a 20th-century artist, shells also serve as a musical instrument.
, Birth of Venus, ,
,
What is the function of the shell in molluscs?
The shell is protection. A kind of natural space suit and the skeleton of a soft-bodied creature, which, if it were not there, would immediately become easy prey for many predators that hunt nearby - from fish in reservoirs to birds and animals in the forests.
So, bivalve molluscs, sensing danger, tightly close the valves. And the disturbed gastropod mollusk not only goes into the shell, but also slams the lid. Everything! Now it is not prey, but only a pebble, among others, hard and inedible. The predator will leave or swim away, having lost interest, and the mollusk, having waited out the danger, will again get out.
Lifestyle features
As a rule, the body of bivalves is symmetrical, slightly flattened. But there are also individuals that look like a ball, as well as worms. Looking at them, you can understand that you do not see either the head or the fins, only the body and the leg, which is located in front.
The latter serves as a motor for them to slowly move along the bottom. First, a limb protrudes from the shell, which clings to the ground, and then pulls the shell towards itself. Thanks to this part of the body, the mollusk can burrow into the sand.
And all this is placed in a calcareous shell, which consists of two plates that interlock with each other. The size of these valves can vary from a couple of millimeters to one and a half meters. They can be equal in size and different in size.
From the inside, they, as a rule, have a very beautiful pearl color, because they are often covered with a mother-of-pearl coating. The older the water creature, the thicker this layer. When a mote gets inside the shell, the mother-of-pearl envelops it, and so the beloved by many pearls turn out.
Outside, they are not so attractive - the stratum corneum is most often brownish and loose. It forms the connective tissue that connects the "doors" of the shell. They grow together at the back and side. However, not completely, leaving a hole for the leg. In order for the clam house to close, he needs to use a special. closing muscles.
A tight connection is also provided by the teeth that run along the edges of the valves. In addition, thanks to such a device, the sashes will not fidget, and are clearly fixed. However, not all representatives that are included in the class of bivalve mollusks have such protrusions.
The mollusk grows like this: along the edge of the shell, due to special secretions, one strip per year is added. So, the age of creation is not difficult to determine. The body increases due to the accumulation of the mineral base. They are real centenarians, their age reaches five hundred years.
The second largest group of mollusks after gastropods consists of more than 20 thousand species. All these species are benthic, i.e. bottom. Bivalve mollusks live at the bottom of reservoirs with fresh or salt water. Most Bivalvia are extremely slow or almost immobile.
Bivalve mollusks lead an inactive lifestyle at the bottom of water bodies.
The depths at which different species of the Bivalvia class live vary from the tidal coastal zone to sea trenches 10 km deep.
Bivalve molluscs feed on organic particles and small plankton. By filtering the water suspension with the help of gills, they realize two functions at once: respiration, absorbing oxygen from the water, and nutrition, filtering out edible particles.
Some groups of laminabranchs have interesting adaptations to life on rocks. Species belonging to the genus Pholas, for drilling passages in stones, have sharp teeth at the front end of the shell. And another type of marine bivalve molluscs, called the sea date (Lithophaga), although it does not have a drilling apparatus, is also able to penetrate stones, dissolving them with acid, which is secreted by special glands.
