Organs of excretion in mollusks. Structure of mollusks

There are many types of animals.These are flat worms, coelenterates, and annelids, and arthropods, and echinoderms, and chordates. Science, which deals with their study, is called biology. Molluscs are also one of the types of animals. They will be discussed in this article. There is also a special branch of biology, which studies this group of animals. It is called malacology. And the science that studies the shells of shellfish is conchology.

General characteristics of mollusks

Representatives of this type are also called spineless. They are quite diverse. The number of species is about 200 thousand.

This group of multicellular animals is divided into eight classes:

• Two-winged.
• Tangled.
• Borozdychatryuhie.
• Yawn-tailed.
• Monoplakophores.
• Gastropods.
• Lopatopods.
• Cephalopods.

The organism of all these animals is arranged according to the same principle. Further, the characteristics of mollusks will be considered in more detail.

Systems of organs and organs

Mollusks, like many multicellular animals, are built from various types of tissues that are part of the organs. The latter, in turn, form systems of organs.

The structure of mollusks includes the following systems:

• the circulatory;
• the nervous system and the senses;
• digestive;
• excretory;
• respiratory;
• Sexual;
• integument of the body.

Let's look at them in order.

Circulatory system

In mollusks it is not closed type. It includes such bodies:

• a heart;
• vessels.

The heart of the mollusks consists of two or three chambers. This is one ventricle and one or two auricles.

Many biting blood have unusualbluish color. This color is given to it by the respiratory pigment hemocyanin, whose chemical composition includes copper. This substance performs the same function as hemoglobin.

The blood of the mollusks circulates in this way: from the blood vessels it pours out into the spaces between the organs - lacunae and sinuses. Then she again gathers in the vessels and goes to the gills or the lung.

Nervous system

In shellfish, it is of two types: a staircase and a sparse-nodal type.

The first is constructed in this way: there is an oclo-cell ring, from which four trunks depart. Two of them innervate the leg, and the other two - the innards.

Nervous system of a diffuse-nodal typeis more complicated. It consists of two pairs of nerve chains. The two abdominal organs are responsible for the innervation of the internal organs, and the two pedals are responsible for the legs. On both pairs of nerve chains there are nodes - ganglia. Usually their six pairs: buccal, cerebral, pleural, pedal, parietal and visceral. The first innervate the pharynx, the second - the tentacles and eyes, the third - the mantle, the fourth - the leg, the fifth - the respiratory organs, the sixth - the other internal organs.

Sense organs

There are such organs of mollusks that allow them to receive information about the environment:

• tentacles;
• eyes;
• statocysts;
• ophradia;
• sensory cells.

Eyes and tentacles are located on the head of the animal.The Osfradii are not far from the base of the gills. These are the organs of chemical sensation. Statocysts are organs of equilibrium. They are on their feet. Sensory cells are responsible for the sense of touch. They are located on the edge of the mantle, on the head and foot.

Digestive system

The structure of mollusks provides for the presence of the following organs of this tract:

• pharynx;
• esophagus;
• stomach;
• the middle gut;
• the hindgut.

There is also a liver. Cephalopods also have pancreas.

In the throat of the soft-bodied there is a special organ for grinding food - radula. It is covered with prongs of chitin, which are updated as the old ones are worn.

Mucus secretion organs

This system is represented by the kidneys. They are also called metanephridia. The organs of secretion in mollusks are similar to those of worms. But they are more complicated.

The organs of excretion in mollusks look like a set of sinuous glandular tubes. One end of metanephridium opens into a coelomic sac and the other to the outside.

Isolation organs in molluscs may be presentin different numbers. Thus, in some cephalopods there is only one metanephridia located on the left side. In monoplacophores, there are as many as 10-12 excretory organs.

The metanephridia of mollusks accumulate excretory products. They are presented by lumps of uric acid. They are excreted from the body of an animal once every two to three weeks.

Also part of the excretory system in mollusks can be called the atrium, which are responsible for the filtration of blood.

Respiratory system

In different mollusks it is represented by variousbodies. Thus, most gingivores have gills. They are also called ktenidiyami. These are paired bilaterally pinnate organs. They are located in the cavity of the mantle. Molluscs, which live on land, instead of gills, there is a lung. It is a modified mantle cavity. Its walls are permeated with blood vessels.

Dermal respiration is also an important place in the gas exchange of mollusks.

Sexual system

It can be arranged in different ways, because amongthere are hermaphrodites and dioecious species. In the case of hermaphroditism during fertilization, each individual acts simultaneously as a male, and as a female.

So we examined all the systems of the organs of mollusks.

Covers of the body of mollusks

The structure of this element differs among representatives of different classes.

Let's look at the different versions of body covers that mollusks can have, examples of animals that belong to a particular class.

Thus, in the furrows and petiolesare represented by a mantle that covers the whole body, with a cuticle consisting of glycoproteins. Also there are spicules - a kind of needles, which consist of lime.

In bivalves, gastropods, cephalopods,monoplacophora and spade-eared there is no cuticle. But there is a shell, which consists of one plate or two in the case of bivalves. In some orders of the class of gastropods, this part of the cover is absent.

Features of shell construction

It can be divided into three layers: outer, middle and inner.

The outer shell is always constructed fromorganic chemical. Most often it is conchiolin. The only exception to this rule can be considered the mollusc Crysomallon squamiferum from the class of gastropods. Its outer shell layer consists of ferrous sulphides.

The middle part of the shell of mollusks consists of columnar calcite.

Inner - from lamellar calcite.

So we examined in detail the structure of mollusks.

Conclusion

As a summary, let's briefly consider the main organs and systems of the bodies of soft-bodied animals in the table. We also give examples of mollusks belonging to different classes.

Now consider the representatives of different classes of the Mollusca type and the features of their structure.

Here we have considered the features of the structure of the main representatives of the Mollusca type.