Excretory organs in mollusks. Mollusk structure

There are many types of animals. These are flatworms, and intestinal, and annelids, and arthropods, and echinoderms, and chordates. The science that studies them is called biology. Mollusks are also one of the types of animals. They will be considered in this article. There is also a special branch of biology that studies this group of animals. It is called malacology. And the science that deals with the investigation of mollusk shells is conchology.

General characteristics of mollusks

Representatives of this type are also called soft-bodied. They are quite diverse. The number of species is approximately 200 thousand.

This group of multicellular animals is divided into eight classes:

• Bivalve.
• Armored.
• Fissured belly.
• Pit tail.
• Monoplacophores.
• Gastropods.
• Shovel
• Cephalopods.

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

Organ systems and organs

Shellfish, like many multicellular animals, are built from various types of tissues that make up the organs. The latter, in turn, form organ systems.

The structure of mollusks includes the following systems:

• circulatory;
• nervous system and sensory organs;
• digestive
• excretory;
• respiratory
• sexual
• integument of the body.

Let's look at them in order.

Circulatory system

In mollusks, it is of an open type. Its structure includes such bodies:

• heart;
• vessels.

The mollusk heart consists of two or three chambers. This is one ventricle and one or two atria.

Many soft-bodied blood has an unusual bluish color. This color is given to it by the respiratory pigment hemocyanin, whose copper composition is copper. This substance performs the same function as hemoglobin.

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

Nervous system

In mollusks, it comes in two varieties: ladder and scattered-nodal type.

The first is constructed in this way: there is a near-pharyngeal ring, from which four trunks depart. Two of them innervate the leg, and the other two - the insides.

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

Sensory organs

There are such mollusk organs that allow them to receive environmental information:

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

The eyes and tentacles are located on the head of the animal. Osfradia are located near the base of the gills. These are the organs of chemical sensation. Statocysts are organs of balance. They are on the foot. Sensory cells are responsible for 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;
• middle intestine;
• hind gut.

A liver is also present. Cephalopods also have a pancreas.

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

Excretory organs in mollusks

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

Excretory organs in mollusks look like a collection of sinuous glandular tubes. One end of methanephridia opens into the coelomic sac, and the other outward.

Excretory organs in mollusks may be present in different numbers. So, some cephalopods have only one methanephridia located on the left side. In monoplacophore, as many as 10-12 organs of excretion are observed.

In mollusk methanephridia, excretion products accumulate. They are represented by lumps of uric acid. They are excreted from the body of the animal once every two to three weeks.

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

Respiratory system

In different mollusks, it is represented by various organs. So, in most soft-bodied gills are present. They are also called ctenidia. These are paired bilateral pinnate organs. They are located in the cavity of the mantle. In mollusks that live on land, instead of gills, there is a lung. It is a modified mantle cavity. Its walls are penetrated by blood vessels.

Also an important place in the gas exchange of mollusks is skin respiration.

Reproductive system

It can be arranged in different ways, since among the mollusks there are hermaphrodites and dioecious species. In the case of hermaphroditism during fertilization, each individual acts both as a male and as a female.

So we examined all the systems of mollusk organs.

Shells of the mollusk body

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

Let's look at the various body covers that mollusks may possess, examples of animals that belong to a particular class.

So, in grooved-bellied and pit-tailed integuments, they are represented by a mantle that covers the entire body, with a cuticle consisting of glycoproteins. There are also spicules - a kind of needle that consists of lime.

Bivalves, gastropods, cephalopods, monoplacfors, and lopatopods lack a cuticle. But there is a sink, which consists of one plate or two in the case of bivalves. In some detachments of the class of gastropods, this part of the integument is absent.

Shell features

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

The outside of the sink is always built from an organic chemical. Most often it is conhiolin. The only exception to this rule is the mollusk Crysomallon squamiferum from the gastropod class. His outer shell layer consists of ferrum sulfides.

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

Internal - from lamellar calcite.

So we examined in detail the structure of mollusks.

Conclusion

As a result, we briefly consider the main organs and systems of soft-bodied organs in the table. We also give examples of mollusks belonging to different classes.

Now consider the representatives of various classes such as Mollusks and the features of their structure.

So we examined the structural features of the main representatives of the type Mollusks.