gastropods or snails are considered a rather large class of animals, which today has about 100 thousand species.Almost all members of the group were ancient marine organisms that are passed to the process of evolution of terrestrial and freshwater survival.Known and shellfish parasites, but not so much.Interestingly, some species have moved to the second water way of life, their ancestors were terrestrial organisms.
Gastropods: body structure
body of representatives of this type is divided into a head office, torso, muscular foot.At the head of most species have one or two pairs of tentacles.As for the trunk, it is asymmetrical and is completely in the sink.Sink in gastropod whole and forms a spiral with different number of curls.The foot is used for moving and fixing - on the lower side has a special sole.In case of danger head and leg tightened inside the shell.
mantle cavity of the animal is in the lower shell turns.These ducts open excretory system, as well as the anus.Some of the class here is the exit ducts of the reproductive system.Interestingly, part of the mantle at the marine life has evolved to the gills, and the terrestrial inhabitants of the lungs are contained.
Integument presented epithelium, which is rich in specific glands that produce mucus.
Gastropods: internal structure
Digestive system begins oral cavity, a hole which is located on the underside of the head of department.The pharynx is a specific entity called radula, which is a chitin grater by which food is ground and into the esophagus.Next comes the stomach (here open hepatic ducts) and the intestine, ending hole.
excretory system in most species represented by one kidney, although there are animal and two bodies.The circulatory system refers to the lacunar type and consists of the heart and vascular system gaps.
respiratory system represented by the gills or lungs.In guinea representatives usually ctenidium can be seen, primary or gills.In the same species that have moved to a second aqueous subsistence gill function takes the mantle.Terrestrial representatives are characterized by a complex respiratory system, which consists of a lightweight system and tracheal tubes, which diverges and carries the air to all parts of the body.
well formed and the nervous system, which refers to the diffusely-node type.Most animals have five pairs of basal ganglia.It is worth noting and well-developed sense organs, including the eyes and tactile receptors.
Gastropods can be either dioecious (marine species) and hermaphroditic (terrestrial and freshwater representatives).Fertilization usually occurs in the female body, after which she lays eggs.Interestingly, at a time gastropod lays several eggs at once, forming masonry.
eggs coated capsule with a small lid on the top.Sometimes the outside of the masonry via the mucus attached infertile, empty capsules.This technique is protective in nature - predator gnaws several blank egg and then leaves.As for development, it can be both direct and to produce larvae.
Gastropods: the most popular forms
The most famous member of the class is the so-called snail.It should be noted that large groups of these animals could harm the grape harvest.At the same time, specially grown snails in some countries are considered to be an expensive delicacy.
And some housewives sign Slug - a small shellfish with reduced sink, which feeds the plants.This is a real pest of vegetable crops, so the population used for the destruction of chemical substances.