Animals

Animals 

one of the two main groups of living things (the other is plants).

All animals are heterotrophic organisms, that is, they feed on ready organic compounds and are unable to assimilate inorganic matter. Among the unicellular organisms there are forms (for example, Euglena) that seem to be transitional in type of metabolism between the animals and the plants, combining heterotrophic and autotrophic metabolism. Active locomotion is characteristic of many animals; some animals (for example, squids, dolphins, cheetahs, martens) are able to move swiftly in water, on land, or in the air.

Animals are divided into two main groups, with different levels of organization: the protozoans (sarcodinians, flagellates, sporozoans, cnidosporidians, infusorians) are unicellular organisms; all other animals are multicellular. The cells that make up their body are qualitatively (morphologically and physiologically) differentiated and form various tissues and organs. As the organic world evolved, the structure and functions of animals became increasingly complex, and locomotor, digestive, excretory and genital, respiratory, cardiovascular, and nervous systems and sense organs appeared. Adaptations arose to maintain biochemical homeostasis. Special, complex patterns of behavior also developed (for example, the courting dances and games of insects, birds, and mammals).

For purposes of comparative study, both extant and extinct animals are classified in a system from lower animals to higher, based on the findings of embryology, paleontology, comparative anatomy, physiology, and biochemistry. There are about 1.5 million known living animal species. Various taxonomists count from 10 to 33 animal phyla. There are 16 generally recognized phyla: Protozoa, Porifera, Archaeocyatha (extinct), Coelenterata, the lower worms, Mollusca, Arthropoda, Prosopygia, Camptozoa, Prodaxonia, Brachiopoda, Pogonophora, Echinodermata, Chaetognatha, Hemichordata, and Chordata (which includes subphylum Vertebrata). A substantial number of the above phyla are found mainly in the seas. The arthropods and annelids exceed all the other animal groups in the number of known species (over 1 million).

Zoology and many of its specialized fields, such as arachnology, helminthology, ichthyology, ornithology, protistology, and entomology, are engaged in the study of animals.

Animals play an important part in the life of man. They serve as sources of food and industrial raw materials, and they are used for work. The rapacious extermination of wild animals has led to the total or partial obliteration of many species, including the dodo, the passenger pigeon, the royal albatross, the white oryx, Steller’s sea cow, and the bison.

The conservation of nature includes the preservation of the natural landscapes that animals need to exist. The establishment of sanctuaries, national parks, and other protected areas enables species of useful animals to survive and reproduce.

Among the animal pests, some are parasites of domestic animals. Others are transmitters of the causative agents of various diseases (for example, the housefly transmits the causative agents of influenza, tuberculosis, dysentery, typhoid fever, and poliomyelitis; fleas transmit the causative agents of plague; and ticks, those of various encephalitides). Still others are forest, cultivated plant, and food pests (for example, fruit moths, locusts, and various rodents). A final group attacks structures (for example, termites and certain beetles). Study of the various aspects of animal life can help to modify the animal and plant worlds in a planned manner, a matter of particular significance in the efforts to solve the problems connected with the transformation of nature.

V. A. SVESHNIKOV