The world of the living creatures that inhabit our planet is extremely diverse. Some of them live only in the aquatic environment, others have adapted to spend part of their lives in water, and some on land. And each species of living organisms is adapted to its environment. The respiratory organs of animals are different, and their type and structure depend not only on where they live, but also on the complexity of the body.
The simplest and most primitive animals are unicellular, which include, for example, amoeba, ciliates, slippers, sporozoans. Their respiratory organs are not formed. They breathe oxygen, which is dissolved in water. That, in turn, enters the body through the surface of the body using osmosis.
In gastrointestinal (sponges, hydra, jellyfish, corals), which are multicellular animals, breathing also occurs through the surface of the body. This suggests primitive structural features of the intestinal.
Most non- parasitic worms have skin respiration, that is, oxygen penetrates through the skin, but in aquatic annelids special respiratory organs appear - gills. The spinal tendril or parapodia is converted into gills. Parasitic worms (flukes, round) do not have respiratory organs, they have anaerobic respiration.
Arthropods include a large number of organisms that live in all environments, therefore their respiratory organs are diverse. Terrestrial arthropods (spiders, scorpions, insects) form special respiratory organs - pulmonary sacs, trachea, lungs.
In scorpions and primitive spiders, breathing is carried out at the expense of the lung sacs. These are deepening of the abdominal cavity, which are filled with hemolymph and contain numerous leaf-shaped plates. Gas exchange occurs through the walls of these plates, oxygen enters the pulmonary sac through the spiracles, which are located on the abdomen. Most spiders have both lungs and trachea at the same time.
Tracheas are thin tubes penetrating the entire body of an animal. Using the holes of the trachea open outwards, on the first segment of the abdomen. The lungs have a primitive structure, and therefore the trachea is better adapted to breathing atmospheric oxygen.
The respiratory organs of insects are also trachea that penetrate the entire body. They seem to branch, enveloping all the internal organs of the animal. Tracheas end with even thinner tubes - tracheoles, which penetrate into the cells. Insect tracheas freely communicate with the environment, but at their ends they have closure devices, due to which water losses during insect flight are reduced.
Arthropods that inhabit water bodies (crayfish, crabs, daphnia, horseshoe crabs) breathe with the help of skin gills. These gills are located on the limbs of the animal and have a large number of thin plates through which the exchange of gases takes place. On land, the animal remains alive while these plates are wetted with water.
The respiratory organs of mollusks can be the gills and lungs. Land or freshwater gastropods mollusks breathe lightly . The mantle cavity of these snails in the process of evolution turned into a lung. This lung has a breathing hole that is associated with the environment and may close.
Freshwater gastropods breathe atmospheric air, for inhalation they rise to the surface of the water. The walls of the lung are densely entwined with blood vessels, since here the blood is enriched with oxygen and carbon dioxide is released. Sea mollusks breathe with the help of gills. Gills are a trellised plate covered with ciliated epithelium. Using the cilia of the ciliated epithelium, water is introduced into the mantle cavity. This water brings oxygen, which is oxidized in the gills. Nutrients also enter the body with oxygen, and the decay products, together with carbon dioxide, are removed through the siphon of the mantle cavity.