Gastropod mollusks: structure, vital activity, reproduction

Gastropods or snails are considered a fairly large class of animals, which today has about 100 thousand species. Almost all the ancient representatives of the group were marine organisms, which in the course of evolution passed to terrestrial and freshwater existence. Clams and parasites are also known, but not so many. It is interesting that some species receded to the aquatic mode of life, their ancestors were terrestrial organisms.

Gastropod mollusks: the structure of the body

The body of representatives of this type is divided into the head part, trunk, muscular leg. On the head, most species have one or two pairs of tentacles. As for the trunk, it is asymmetrical and completely in the sink. The shell in the gastropods is one piece and forms a spiral with a different number of curls. The leg serves to move and fix - on the underside there is a special sole. In case of danger, the head and leg are tightened inside the shell.

The mantle cavity of the animal is in the lower coils of the shell. This opens the ducts of the excretory system, as well as the anus. Some representatives of the class also have ducts of the reproductive system. It is interesting that part of the mantle of the marine inhabitants turned into gills, while land inhabitants have lungs here.

The covers of the body are represented by the epithelium, which is rich in specific glands producing mucus.

Gastropod mollusks: internal structure

The digestive system begins with the oral cavity, the opening of which is located on the underside of the head region. In the throat there is a specific formation called radula, which is a chitinous grater, by means of which food is ground and enters the esophagus. Then comes the stomach (the hepatic ducts open here) and the intestine, which ends with a hole.

The excretory system in most species is represented by a single kidney, although there are animals and with two organs. The circulatory system belongs to the lacunar type and consists of the heart, a system of lacunae and vessels.

The respiratory system is represented by gills or lungs. In marine representatives, as a rule, one can notice ktenidia, or primary gills. In the same species, which again passed to water existence, the gills perform the function of the mantle. Ground representatives are characterized by a more complex respiratory system, which consists of a lung and a system of tracheal tubes that diverges and carries air to all parts of the body.

Well formed and the nervous system, which is classified as diffuse-nodal type. Most animals have five pairs of major ganglia. It is worth noting well developed senses, including the eyes and tactile receptors.

Gastropods can be both dioecious (marine species) and hermaphrodites (terrestrial and freshwater representatives). Fertilization, as a rule, occurs in the body of a female, after which she lays eggs. It is interesting that at one time the gastropod mollusks postpone several eggs at once, forming a masonry.

Eggs are covered with a capsule with a small lid on the top. Sometimes, to the outside of the masonry, with the help of mucus, unfertilized, empty capsules are attached. This method is protective - the predator gnaws several empty eggs, then leaves. As for development, it can be either direct or with the formation of larvae.

Gastropod mollusks: the most popular species

The most famous representative of the class is the so-called grape snail. It is worth noting that large groups of these animals can damage the harvest of grapes. At the same time specially grown snails in some countries are considered an expensive delicacy.

And some owners are familiar slug - a small shellfish with a reduced shell, which feeds on plants. This is a real pest of vegetable crops, therefore chemicals are used to destroy populations.