How are shells formed?
- How are shells formed?
If you've ever walked along the beach, you've probably seen seashells lying on the sand where they were washed up by the waves. Such shells are almost always empty; they are the former home of some dead sea animals.
By the way, shells are found in wooded areas, rivers, and ponds. When people talk about shells, they usually mean the soft-bodied animals known as molluscs.
Most mollusks have a shell that protects their soft body. A shell is the skeleton of a mollusk. It is a part of the animal, and the mollusk is attached to it by muscles. The soft shellfish inside never leaves its home.
The shell is made of limestone by the mollusk itself. Certain glands can take limestone from the water and deposit tiny particles at the edges or along the inside of the shell. As the mollusk grows inside, the shell also increases in size. You can see the growth lines, which are marked by ridges (bulges) running parallel to the outer edge of the shell. You've probably noticed these growth lines on oyster shells. The appearance of other scars is caused by scars on the mollusk's mantle or the muscles of its body.
The shell of a mollusk consists of three layers. The outer one is covered with a layer of horny substance, which does not contain lime. Underneath is a layer of calcium carbonate. The inner layer is the mother of pearls, or nacre. It consists of a very thin layer of calcium carbonate and horny substance.
The color of the shell depends on the color of the substance secreted by some glands of the mollusk. Therefore, the shell can be speckled, plain or painted with stripes and lines. Some shells are so tiny that they can only be seen through a magnifying glass, while a giant sea clam can be up to a meter long. - A shell is both an external skeleton and a house that bivalves and gastropods - and all other mollusks, except for some special groups - such as nudibranchs or octopuses build for themselves. As the mollusk grows, the shell also grows.
The shell, layer by layer, is composed of special cells at the edge of the mantle, capable of forming limestone crystals from salts sea water. In winter, mollusks grow more slowly, and in summer - faster; therefore, seams and convex growth rings remain on the shell (not to be confused with the normal concentric sculpture of a shell, for example in the Venus) - from them you can calculate the age of the mollusk - like from the annual rings on a tree cut.
Most bivalves live on a sandy or muddy bottom, burying themselves entirely in it, and putting out siphons - two tubes through which they suck in and release water. From this water they take both oxygen for breathing and food - microscopic plankton and detritus.
All mollusks know how to make pearls: when, for example, a grain of sand accidentally appears between the shell and the mantle, the mollusk begins to fight the foreign body - the cells of the mantle envelop it with layers of nacre - the same with which they line the inner surface of the shell - a pearl is obtained. Mother-of-pearl is thin plates of limestone, light is refracted and scatters in them into multi-colored rays - so it seems to us that mother-of-pearl has color. Only a few species of bivalves can make precious pearls, and, for example, those of the Black Sea mussel - they look more like large gray grains of sand.
Structure of a bivalve mollusk - Bivalvia
Only a few bivalves live on a solid surface: the mussel Mytilus galloprovincialis and the mytilaster lineatus use a bundle of strong threads - a byssus - to attach to stones and algae stems, and oysters grow to the stone and to each other with their shells. During life, the shells of the oyster Ostrea edulis were white-green-pink, but now we are finding more and more black shells, because they lay for a long time in the ground, where everything turns black from hydrogen sulfide. The stone borer Pholas dactylus drills burrows in rocks with a drill shell.
Venus gallina shells:
on the right - normal color,
black - lay buried in the ground and darkened from hydrogen sulfide, yellow - were thrown back to the surface of the bottom;
white - worn out by sand.
Most of the shells on the beach are donax shells and conch shells - these are the most common mollusks of the sandy shallow waters of the Black Sea, there are a lot of cocked hats Spisula triangula. Everywhere on the sandy beaches of the Black Sea there are tiny firefly shells - lucinella and lentidium. More and more weighty shells of Scapharca inaequivalis - this tropical bivalve entered the Black Sea less than 20 years ago.
Shells or seashells, also known simply as the shell, are the protective outer layer of an animal that lives in the sea. The shell is part of the animal's body. Empty shells are found washed up on beaches. They are empty because the animal died, and its soft parts became food for predators or scavengers, or simply rotted.
The term "shell" generally refers to the exoskeleton of an invertebrate (an animal without a backbone). Most of the shells that are found on beaches are shells sea mollusks.
In addition to mollusk shells, other shells belong to Kamchatka crabs and brachiopods. Marine annelids in the family Serpulidae create cementum shells from calcium carbonate. The shells and molting shells and lobsters are called exuviae. Most shells are external signs.
There are shells of freshwater animals such as freshwater mussels and freshwater snails, and shells of land snails.
The word "barnacles" refers only to the shells of marine molluscs. Shells are part of conchiology. Conchologists, or serious collectors, carefully collect living animals for study so as not to disturb ecosystems.
- The study of all animal molluscs (as well as their shells) is known as malacology;
- A person who studies shellfish is known as a malacologist.
Molluscs shells
Sea shells - "shells" marine species bivalves, gastropods (or snails), scaphopods (or shellfish), polyplacophorans (chitons), and cephalopods (such as Nautilus and Spirula).
Marine species of gastropods and bivalves are more numerous than terrestrial and freshwater species. The shells of marine species in tropical and subtropical regions of the planet are more colorful and larger than in temperate zones and regions close to the poles.
But there are also a huge number of extremely small species - micromollusks.
Additionally, not all molluscs have an outer shell: some molluscs, such as some cephalopods (squid and octopuses) have an internal shell, and many molluscs have no shell at all, such as Nudibranch.
There are more than 15,000 species of bivalves, marine and freshwater: mussels, oysters. Most bivalves consist of two identical shells that are connected by a flexible loop. The animal's body is protected within these two shells. Bivalves that do not have two shells or have one valve - they lack the shell as a whole. The valves are made of calcium carbonate and form the mantle.
Bivalves are also known as pelecypods. These are animal filter feeders: they pass water through gills, which trap tiny particles of food. Some bivalves have eyes and open circulatory system. Bivalves are used throughout the world as food and as a source of pearls. The larvae of some freshwater mussels can be dangerous to fish.
Shell Beach, Western Australia - a beach made entirely of cockle shells Fragum erugatum.
Gastropods. Some types of gastropod shells (shells of sea snails) wash up on sandy and rocky beaches. Numerous Turritella gastropod shells on the beach at Playa Grande, Costa Rica
Polyplacophorans - slabs of chiton tuberculatus from beachdrift on the southeast coast of Nevis, West Indies
Chiton slabs or flaps are often washed on beaches in rocky areas where chitons are common. Chiton shells, which consist of eight separate plates and a belt, usually come apart not long after death, so they are almost always found as dismembered plates. Plates of large types of chitons are sometimes called “butterfly” shells because of their shape.
Cephalopods. Sepia Cuttlefish Shells. Only a few species of cephalopods have shells. Some cephalopods, such as sepia and cuttlefish, have a large internal body.
Spirula deep-sea - has an internal shell (about 1 or 24 mm), but is very light. This chambered shell floats very well and is therefore easily accessible to adventurers in the tropics.
Nautilus is the only one among cephalopods that has a well-developed outer shell. Female cephalopods of the genus Argonauta create an egg that is sometimes found on tropical beaches and is called the “paper” Nautilus.
The largest group of cephalopods, the ammonites, are extinct, but their shells are very common in some areas as fossils.
Shells are a “free” resource in the intertidal zone and shallow subtidal zone. As such, shells are sometimes used by people for a variety of purposes, including construction.
Xenophoridae are marine gastropods, rather large sea snails.
The ocellated (spotted) octopus uses clamshells as shelter.
Small octopuses sometimes use the empty shell as a sort of cave to hide, or keep the shell around them as a form of protection, like a temporary fortress.
Invertebrates. The marine hermit crab, like Diogenes, uses the shell of Nassarius reticulatus.
Almost all hermits “carry” empty gastropod shells throughout their lives in order to protect their soft bellies from predator attack. Each hermit is forced to find the shell of another gastropod.
Numerous small and inconspicuous species of mollusks (micromollusk) have not yet been identified according to zoological nomenclature (ICZN). A large number of new species are described in the scientific literature every year. Currently, there are an estimated 100,000 species of shellfish worldwide.
We can talk about barnacles animals, which are closely related to lobsters and crabs. They are part of the crustacean subphylum, infraclass Cirripedia. This type of arthropod can be found in tidal waters and shallow waters. They are sea animals. There are about 1220 species of mollusks in total.
In order to live, mollusks permanently attach a solid base to their body.
Pedunculata barnacles live by using a stem to anchor their body to a hard substrate. On the other hand, Acorn shells use growing shells to attach the body.
Another lifestyle of free living Barnacle shellfish. They can be seen fixed from below, they are attached using cement glands to the substrate.
If you think that shells have a heart, then you are mistaken. This animal has no true heart. The part of the body that can function as the heart is located near the esophagus. A series of muscles pump blood through the sinuses.
Mollusks do not have any gills. Oxygen in water enters through the internal membrane located on the shell and limbs. The maxillary glands are considered to be the excretory organs of shells.
You can find one eye in adult clams. Thus, animals can only sense dark and light areas.
There are two larval stages in life cycle shells - nauplius and cyprid. After surviving the larval stages, the barnacles will develop into adulthood.
There are only a few species of hermaphroditic mollusks - gonochoric or androdioecious animals. In most of them, the testes are located in the back, and the ovaries are located in the stalk or base.
One of the reproduction methods is spermcasting. The male releases sperm into the water, and the female picks it up to fertilize the eggs.
You can find shells living in shallow waters. Depth less than 100 meters.
Seashells at Holyhead, Wales
Most species are harmless because when attached, they do not interfere with the animal's food chain and do not harm the animal. Many types of shellfish are so harmless that, in fact, an animal that is covered in them may not even notice them!
Barnacles typically live between 5 and 10 years, but some of the larger species are much older.
Mollusks attach to animals in the larval stage. Once the baby clam has effectively glued itself to something solid, a thin layer of flesh wraps around the clam's outer shell. When a baby clam fixates itself on something, then, as a rule, it spends the rest of its life there.
Shellfish are filter feeders (also known as seston feeders) - they feed on food particles extracted from the water. The shell of a mollusk consists of a series of plates (usually 6), with feathery foot-like appendages that scoop water up to the shell to feed.
Mollusks have numerous predators. The larvae of the mollusk are so small that they float along with the plankton in the water. As you know, there are shells that are edible for humans ( edible species mollusk) in parts of Europe, Spain, Portugal.
Shells are believed to be some of the oldest surviving creatures on the planet. Their age dates back millions of years. During this time, the mollusks have changed little.
Despite the increased levels of pollution and changes in the water, barnacles are believed to be one of the few animals that are not greatly affected.
In different places around the world, fishermen use some parts of local plants, roots, leaves, juice, to poison or stupefy fish so that they float to the surface where they can then be easily collected. For the same purpose, in extreme situations, you can use bivalve shells or mollusks.
Most plants suitable for poisoning fish in water bodies grow in southern and tropical climatic and geographical zones. For example:
— Derris bush and Barringtonia tree — from South-East Asia to Australia.
— Desert Rose — Africa and the Arabian Peninsula.
- Juice of the Assaku bush, shoots of many types of Timbo and Lonchocarpus lianas, roots of the Brabasco tree - in South America.
— Poultry grass and Virginian goat's rue — North America.
On the territory of the CIS countries there is only one plant suitable for such purposes - Djungarian mullein, which grows in the mountains Central Asia at altitudes up to 2600 meters. Therefore, the likelihood that if you find yourself in a situation you will find, identify and be able to use one of the above-mentioned plants is negligible.
A more realistic way only in a truly hopeless extreme situation!, poison the fish, and then collect it, use it for food, do this using ordinary bivalve shells and other mollusks, or rather their shells. In addition, shell meat itself is suitable for use as food or bait for fishing. However, we will present everything in order.
Bivalve shells as food in extreme situations.
Almost all bivalve mollusks of fresh and slightly salty waters, that is, rivers, streams, swamps, lakes and seas, are considered edible - such as, for example:
— Toothless from 8 to 20 cm long. They are found at the bottom of standing and slowly flowing reservoirs with silty soil.
— Perlovitsy from 5 to 10 cm long. They live mainly in flowing water, in reservoirs with sandy soil.
— Sharovka 2 to 3 cm long. They can be found in the sand and silt of various bodies of water, almost round in appearance and yellowish or yellow-brown in color.
Preference for eating should be given to pearl barley, which is easy to spot by the paths it leaves as it moves along the bottom. At the end of such a path, a prominent tubercle is usually visible - there is a mollusk buried in the ground. Or sometimes it’s enough just to feel the bottom with your bare foot and find a hard ribbed surface, these will be pearl barley shells. In favorable conditions, you can collect more than a bucket of them in 10-15 minutes. When searching for and collecting shells, you should be careful - the shell valves are very sharp and can easily injure.
Recipe for making bivalve shells.
Bivalve shells are prepared in a very simple recipe. We lay them out as close to the fire as possible with the slit facing up; after a while the shells will open. In the opened shell we find a scallop - this is the edible part of the shell, cut it off and fry it over the fire. If you have a cauldron, then after washing the shells, you can boil them in the shells and after the shells open, cut out all the meat and eat.
Or first cut the constipation muscles by inserting a knife through the gap between the valves, and then cook. Even pearled pearls caught in clean, spring water can smell strongly of mud. If there is salt, for a more pleasant taste, the shell meat should be salted during cooking.
Bivalve shells as bait for fishing.
The pearl barley shell is perfect for catching tench, bream, carp, catfish, large crucian carp and many other fish. We open the shell using one of the methods described above, use a knife to separate the meat from the shells and place it on the hook.
Bivalve shells as a poison for fishing.
The shells of mollusks partly consist of a special nitrogenous, chitin-like substance - conchiolin, usually impregnated with lime. It is this lime that can be used to poison fish, but first it must be extracted from the shells themselves. To do this you need:
1. Collect shells in an amount equal to the volume of 4-5 buckets.
2. Open the shells and clean them of entrails, which can be used as bait or for food (see text above).
3. Break the peeled bivalve shells and grind them between stones, the finer the better, almost to a powder.
4. Mix the resulting powder with charcoal in a 1:1 ratio.
5. Burn the resulting mixture over a strong fire until it begins to turn brown and then turn white.
6. When the mixture begins to turn white, remove from heat.
7. Throw the resulting lime into the water and wait until the fish floats up.
A few important notes on using bivalve shells as fish poison.
The method described above for obtaining fish by poisoning it is poaching, therefore it is permissible only in extreme situations that threaten health and life!
— Fish poisoned with such lime is safe for human consumption.
— The method is quite effective only in any stagnant or weak-flowing water.
“If this method is used in closed reservoirs, then you can destroy all the fish there, thus depriving yourself of a source of food for the future and causing harm to the environment.
“However, if you poison fish in a natural or artificially created coastal backwater, then soon the usual number of fish in it will be restored.
Natalya Bernazh-Gorbenko
One day while walking we found a little shell with a hole. Naturally we had questions:
What is it for? hole?
How many years shell?
This is an adult shell or baby shell?
Who lived in this shell?
-Hole Was it always there or did it appear later? and why?
First we remembered what we know about shells. It turned out not so much.
From the book we learned that mollusks live in such shells. A shells They are called bivalves because they consist of two parts - valves, and live both in the sea and in salty sea water.
We also learned that age shells can be recognized by stripes-lumpy growths around the circumference of the shell. How many stripes, so many years. Let's do the math.
But what is it for? hole in the sink? This question gives us no rest.
We put forward our hypotheses.
Marika and Lera's version: -Need a hole to breathe.
Marika spent time with her mother study and told us a lot of interesting things. Having examined the structure of the mollusk, she found out. THAT THE MOLLUSK BREATHES OXYGEN contained in water. For breathing and feeding, there are special siphon openings at the shell; it is through them that the mollusk sucks in water. This is how he eats and breathes. Marika's hypothesis that hole is needed for breathing. not confirmed.
Matvey's conjecture: The hole was made by a fish - a needle.
Matvey was given a task: together with your mother, read about the needle fish and tell us about it and test your hypothesis.
Matvey told us a lot of interesting things about needle fish. It turns out that she doesn’t eat shellfish at all. and by small crustaceans - plankton. We also learned that the needle fish is a close relative seahorse. And the needle-like growth is soft and incapable of digging through a thick and strong shell. Matvey’s version was also not confirmed. We decided to do it ourselves hole in the sink.
Matvey was the first to complete the task. hole he did it with a screwdriver and dad. Roma did hole using a sharp screw yourself!
And Lisa decided that hole can be burned off with acid. With the help of her mother, she carried out her experiment. Unfortunately, the hole didn't appear.
Now we know that hole someone is drilling. But who?
Lisa, Matvey, Marika and Roma on different paths learned: he makes the hole who really wants to eat tender shellfish meat. We learned that the mollusk has enemies - starfish and rapana - predatory mollusks.
Lisa went on an excursion to the aquarium. She learned that starfish don't hole in the sink. she opens the shell doors with her rays.
On the Internet we found articles about rapana. This is the largest snail, one of the most ferocious predators! Young rapana drill holes in the shells of bivalves with their tongue-drill, and adults open their shells with a muscular leg and eat the opened mollusks.
We also learned that the Rapanas moved from Sea of Japan to Chernoe. Now in the Black Sea, due to rapana, there are almost 2 times fewer mollusks than 40-50 years ago. Rapana have proliferated greatly due to the fact that their main enemies, starfish, are absent in the Black Sea due to low salinity. Starfish eat rapan in their homeland - Pacific Ocean. So that's who does it holes in the shell!
The following mollusks live in the Black Sea:
- teredo and rapana
- Venerka and Donax
- heart shapes and scaparis
- byssus and calyptreas
- stone cutters and folas
- oysters and scallops
We will tell you in more detail about the details of the life of each of these mollusks, the history of origin and appearance in the Black Sea.
Which mollusk in the Black Sea has a drill on its nose?
The little Teredo shipworm was once the terror of everyone traveling the world. This a bivalve mollusk that looks like a worm, with its shell at the front end of the body, drilled many passages in the wood from which the ships were made, and turned them into dust. Teredo eats wood and lives in it. Now people have figured out how to protect the wooden lining of ships with the help of a poisonous impregnation, and the teredo mollusk drills into pieces of wood and tree branches that fall into the sea.
Where does the shipworm come from in the Black Sea?
This is what Mangrove trees look like. The shipworm lives on their roots.
Natural shipworm habitat mangrove forests. Their closest location to the Black Sea is the Persian Gulf. Keeping individuals in ports Persian Gulf reaches 50 per square centimeter. It is believed that it was from here that this mollusk was brought to the Black Sea in the body of merchant ships. More recently, in the 50s of the 20th century, a shipworm destroyed piles in the Black Sea ports in just 2 years. This is not surprising, considering that its length can reach 1 meter; in the Black Sea, the documented length of the shipworm is 62 centimeters, and the channels that it leaves in the wood reach 2 m in length and 5 cm in diameter.
Where did rapana come from in the Black Sea?
These large sea snails with beautiful shells decorated with orange mother of pearl are uninvited guests in our sea. Perhaps they sailed from the Pacific Ocean on the bottom. Rapana females lay eggs on hard objects: on sticks, on the backs of crabs, and even on the shells of their relatives. This is how caviar travels across the seas and waves in hard protective tubes.
In 1947, a new inhabitant was first discovered in the Black Sea - predatory rapana snail.
Which carnivorous mollusk has teeth on its tongue?
The seemingly harmless rapan turned out to be a voracious predator. With his tongue, the radula, he drills into the shells of bivalves, injects poison and paralyzes the inhabitant of the shell. Then he opens the shell and sucks it out.
Who ate all the oysters, scallops and cuttings in the Black Sea?
Although rapan has lived in the Black Sea for only half a century, it has caused great damage to its inhabitants. Unfortunately, in the Black Sea, rapana did not have a worthy opponent who would eat these voracious snails. Rapana is eaten in the Pacific Ocean sea stars, but not salty enough for them. So it turned out that the rapana multiplied and destroyed almost all the scallops, oysters and sea cuttings. And now there are two times less in the Black Sea different types shellfish
Where is the sea date hiding?
In the soft gray-green marl stones you can see passages drilled by mollusks. This is the work of the stone-cutting mollusk - folas or sea date. Folas has a worm-like body, at the front end of which is a shell with denticles, similar to. With the help of this shell, the sea date drills a hole in the stones in order to hide in it. It feeds on plankton.
When and how does a mollusk get its own home?
Homeless larvae of sea mollusks travel through the sea. At this time, future mollusks feed on particles of dead animals, plants and algae. Gradually the body of the larva changes. It settles to the bottom, develops and builds a house, turning into a mollusk that we can see on the beach.
A barnacle is a shell in which a mollusk lives. He builds his house with the help of his body - the mantle. The edge of the mantle deposits layers of shell, forming annual rings, just like those of trees. Thus, it is possible to determine how old the shell is.
The sea wave decorates the sandy shore with many colorful shells. Often shells have the same shape different colors. For example, Venus can be white and black, orange and yellow. The color of shells depends on their living conditions: normal shells are two-colored, those lying in the ground are black, those thrown back to the bottom are yellow. Most often, white shells are found - their upper layers are erased by the sand.
Who locks their sea house?
On the sandy shore you can find a variety of shells - former houses of bivalve mollusks. Mollusks build them themselves, this is their house and their skeleton, which supports and protects the mollusk from danger. Most often on sandy beach meet donaxes, smooth and shiny, so similar to a butterfly. Multi-colored venus, which children sometimes call sailors for their stripes, literally cover the surf. They become a welcome find hearts and large white and red skafarki, discarded storm wave. All bivalve mollusks, at the moment of danger, slam shut on a lock located at the top of the shell. The teeth fit into the depressions and firmly grip the valves, and strong muscles hold the valves so that the mollusk does not become prey for a crab or. Shells vary in the shape of their locks.
Who walks on one leg along the sea path?
Bivalve molluscs move along the seabed with the help of a muscular leg. They pull it out of the flaps, catch on the sand and are pulled to a new place, leaving furrows in the sand behind them. So on seabed intricate patterns appear.
Why are Black Sea mussels called homebodies?
Mussels - bivalve molluscs, but they cannot swim like scallops or move along the bottom and hide in the ground like other mollusks. Therefore, mussels have adapted to attach their shells to underwater rocks using strong threads that their body produces. Mussels live in colonies and hold on to each other for strength. If the mussels have to move to another place, the mollusk separates a bundle of its threads - the byssus, and then releases new threads and plunges them deep into the ground, like roots. Since mussels are homebodies, they are successfully grown on sea plantations. This mollusk is tasty and very healthy for humans; even medicines are made from it.
What clam wears a hat?
Sometimes on the sandy shore there are shells that look like a small cap. Just think, this is the house of a tiny Chinese cap snail - calyptrea, which sits in a small curl! This mollusk has adapted in its own way to living on soft soil: the wide, light cap does not sink into the sand, and the shape of the cap gives stability to the snail’s house.