Mollusk is a unique and ancient representative of the animal world. Thanks to a special kind of protective formation - the sink - it cannot be confused with anyone else. Later in the article we will talk about the function of the shell in gastropods and other invertebrates.
So different mollusks
Shells of mollusks are found both on the seashore, and on the river, and just in the forest. The variety of their shapes and sizes is truly amazing. Elongated, curved, like a spindle, flattened, consisting of two "petals", spherical with a sharp tip and very small, built in the form of a spiral flattened from the sides ...
Some snails are so tiny that you can only see them with a good magnifying glass. But, for example, among the coral reefs of the oceans live huge bivalve mollusks with a shell larger than a meter and weighing more than 300 kg.
The color of the shells is very diverse. It can be plain and modest, or it can be whimsical - decorated with dots, lines and stains.
The general concept of the function of the shell in mollusks in the 7th grade gives us a course of zoology. But in order to thoroughly clarify this topic for ourselves, we first dwell on some points.
Clam species
Shellfish in the world, scientists have counted more than 100 thousand species. The most famous among them are bivalves and gastropods.
Among the typical, that is, the most famous, representatives of mollusks are called gastropods (about 40 thousand species). They live in almost any environment, can move around, and they have a sink.
The body of the gastropod mollusk is divided into a head, leg, equipped with strong muscles, and a mantle. In the oral cavity is the so-called radula (grater), which serves to scrape food from various surfaces. As a rule, these are algae, mushrooms, plants, their rotting remains, carrion.
Slugs are the closest relatives of this species of snails, but they do not have a shell.
Gastropod mollusks live both in water and on land. You saw many of them in forests, gardens and parks. For those who are fond of aquarium, snails (most often these are Achatina) crawl along the glass and the bottom of the aquarium and bring undoubted benefit, clearing them of growing algae. The most common gastropods are the grape snail and the same Achatina. And weirdly curved, with a tip on the end, shells of buccinums (or mollusk trumpeters) we bring with us from the sea as souvenirs.
Among snails there are also predators. The composition of their saliva includes sulfuric acid, with the help of which they dissolve the shell of smaller mollusks and eat it.
In the most inactive, bivalve mollusks (such as oysters, mussels, scallops, freshwater toothless and barley), the shell is divided in two, but there are no legs and head. They donβt even need them - they get bivalve food by opening the sink and filtering the water through special internal siphons. These siphons also serve as gills - with their help mollusks breathe.
Bivalve mollusks can simply lie on the sea or river bottom, can live among corals or partially buried in silt holes. Some species, sticking to stones and various surfaces, literally cling to them. Only very few species of bivalves (scallops) have the ability to swim.
What is a sink?
At its core, it is a shell protecting a living creature or future plant. It can be woody (like a nut), it can be the shell of an egg of a future bird, act as a shell of an insect or crab. In the latter case, fragments of the shell are fastened with soft tissues so that the animal has the ability to move.
The basis for the shells can be wood, lime, bone tissue (like a turtle) and even quartz compounds.
Some shells during the development of a living creature living inside, are destroyed - this happens in a nut when it sprouts, or in a chick hatching from the shell of an egg. Insects survive molting and change their shell for a new one several times during the life cycle.
But all the mollusks, although their name comes from the Latin word Mollusca, which means "soft-bodied", carry their shell with them, building it up throughout life.
How to build a sink
The shell is made by the mollusk itself. Building material for the house is produced by its special glands. They filter out lime particles from the water and grow them along the edges of a still soft and young, received at birth, shell. The mollusk grows up - its body grows, its "spacesuit" also becomes thicker.
Thickening along the edge of the shell in the form of scars - a kind of growth ring, which are in trees. Only in them they are hidden inside the trunk, and in mollusks (for example, oysters) you can easily find them - these thickenings are parallel to the entire edge of the shell.
What does the clam shell consist of
Shell shapes are very diverse. Snails (gastropods) most often have a shell in the shape of a curled cone. The bivalve shell, as the name implies, consists of two interlocking halves.
Slugs and cephalopods (these are predatory inhabitants of the sea kingdom - squid, octopus and cuttlefish) also belong to mollusks, but do not have a shell as such. They have a thickened skin, which scientists consider to be a hidden shell that has undergone evolutionary development. The foot of cephalopods also evolved and turned into tentacles with suction cups.
The shell is usually formed by three layers:
- There is no lime in the outer; it consists of horny matter secreted by the mantle. This protein, called conhiolin, is the strongest among the shell layers. It serves as the most durable protection against the aggression of the world.
- The next layer is calcium carbonate. It is a naturally occurring inorganic chemical compound. It is found both in the form of independent minerals (calcite and aragonite), and rocks. This is chalk, limestone, marble. The calcareous base is part of the shell of bird eggs, it also forms the middle layer of the shell of the mollusk.
- The thinnest is the inner layer of the shell, which is called the "mother of pearls" or mother of pearl. It consists of a mixture of fine particles of lime and organic matter conhiolin.
Mother of pearl, which could be appreciated from a jewelry point of view, however, you will only find mollusks living in warm tropical seas. For example, in the waters of the Red Sea, the Pacific Ocean, in the Persian Gulf.
And in freshwater mollusks that "make" mother of pearl and pearls, there is practically no left.
What is the function of the shell in mollusks?
The sink is protection. A kind of natural spacesuit and skeleton of a soft-bodied creature, which, if it had been without it, would immediately become easy prey for many predators hunting nearby - from fish in ponds to birds and animals in forests.
The function of the shell in mollusks is to be a refuge in which it can hide, as soon as there is any threat to its life.
Thus, bivalve mollusks, sensing danger, tightly close the wings. And the disturbed gastropod mollusk not only goes into the sink, but also slams the lid. Everything! Now this 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, after waiting for danger, will again come out.
Interesting Facts
So, protection - this is the function that the shell of mollusks performs. It would seem that there are no other answers to this question. However, Japanese scientists managed to detect the so-called ability to active self-defense in some species of gastropods. It manifests itself, in particular, in species such as Karaftohelix selskii and Karaftohelix gainesi. They have large sink sizes and a wider hole in the entrance to the "house".
When attacked, for example, by a beetle, the snail can turn its βhouse" almost 180 Β°, tilt it almost horizontally, defending and pushing the attacker away. Of course, the muscles of snails with this ability are more developed than those of their congeners. Moreover, this ability did not appear in related species, as their feature, but was fixed evolutionarily on various habitats.
We hope you have received a fairly complete answer to the question of what function does the shell of mollusks perform.