The large pond is a typical representative of freshwater gastropods. In our article we will consider the living conditions and typical features of the structure of this animal.
Mollusks: features of the organization
Translated from Latin, the name of this type of animal means "soft-bodied." Some of them have shells. But in any case, the body of these invertebrates is soft and non-segmented. You can meet them in fresh and salt ponds. For example, toothless and pearl barley live in ponds and lakes, and mussels and octopuses live in the seas. Snails and slugs can be found on wet land.
In the body of mollusks, three parts can be distinguished: head, trunk and leg. Most of them move quite slowly, since the muscles are represented by separate bundles. In all mollusks, the trunk is surrounded by a fold of skin called the mantle.
Classification Basics
Three classes of mollusks are distinguished depending on the structural features. A characteristic feature of cephalopods is the modification of the legs into tentacles. They are located around the mouth. On the tentacles are suction cups, with which animals catch and hold prey. Cephalopods are capable of reactive movement due to a special tubular formation - a funnel. Representatives of this class are squid, cuttlefish and octopus.
Bivalve mollusks are barley, zebra mussel, mussels and oysters. All of them have a body consisting of a trunk and legs, as well as a shell of two wings. The big pond is a representative of gastropods. Let us dwell on its structure in more detail.
Big Pond - representative of gastropods
A large, or common pond, is found in fresh waters rich in vegetation. His body, like all gastropods, consists of a head, trunk and legs. The middle part is completely located inside a spiral twisted shell, consisting of lime, covered with a layer of horn-like substance. This is a kind of home and shelter. The sink of a large pond is spirally twisted. Maximum count 4-5 revolutions. It has a hole called the mouth. Through it, the head and leg are pulled inward. The sink of a large pond and horn coil in case of danger is closed with a special lid. This structure is an additional defense against enemies.
The structure of a large pond
Why are the mollusks that the pond represents are gastropods? It's all about the structure of their body. There are no clear boundaries between its parts. The leg is a flat and muscular protrusion, completely occupying the abdominal part of the body. Its surface secretes mucus, which provides easy gliding on various substrates and water film.
On the head of a large pond is a pair of tentacles. These are the organs of touch. If you touch them, the mollusk will pull its head into the sink. At the base of the tentacles are the eyes. Pond boats also have balance organs. They are represented by small bubbles, inside which are located special bodies. A change in the position of these structures maintains the balance of the mollusk.
Circulatory and respiratory systems
The large pond has an open- type circulatory system . It consists of a two-chamber heart and vascular system. Blood mixes with abdominal fluid, washing all tissues and organs. From the heart, it enters the arteries, and in the opposite direction moves through the veins. Despite the fact that the large pond is living in water, it breathes exclusively atmospheric oxygen. For this, the animal moves to the surface of the water and opens out the breathing hole located at the edge of the shell. It leads to the lung, in which oxygen enriches the blood.
Digestive and excretory systems
The big pond is moving slowly but surely. Why would he constantly "travel"? The mollusk moves in search of food, scraping it from underwater objects with the help of its jaw and grater. The latter consists of several rows of horn denticles. The process of digestion of nutrients is accelerated by the enzymes of the digestive glands - salivary and liver.
An anal hole opens above the head of the pond. And next to it, the duct of the urinary system opens. The latter is represented by a single kidney and ureter with an opening.
Reproduction and development
By the type of the reproductive system, the large pond is hermaphrodite. This means that both female and male germ cells are formed in his body. The fertilization of these mollusks is internal. As a result, there is an exchange of sperm. Mollusks place zygotes in gelatinous cords that attach to underwater objects. As a result, young individuals with a thin shell develop.
So, to summarize: the large pond is a representative of gastropod mollusks. These are typical inhabitants of fresh water bodies. The ponds have three parts of the body: the head, trunk and leg, as well as a spirally twisted shell.