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Kingdom Animal: facts for kids

Animal Kingdom is one of the two great sections into which biologists divide most living things. The other section is the plant kingdom (See Plants, interesting plant facts). In many cases, the difference between animals and plants is obvious. Plants are fixed in one place; they grow by spreading out; and are mainly green in color. Animals are more compact and move under their own power. However, some microscopic plants can travel about in water by moving tiny hairs. (See What is algae?). The real difference between animals and plants is in their method of feeding. Plants make their own food from simple substances. Animals eat plants or animals that eat plants. Some eat dead matter. However, there are some plants that catch and feed on insects.

Kingdom Animal: facts for kids
The coyote once roamed over most of North America	When roused, the brown bear, a larger member of the animal kingdom, can maim a man with a blow of its claws

Other differences arise from the different feeding methods of animals and plants. Firstly, animals have to move about and most animals have far more accurate and sensitive senses than plants. They detect more precisely what is happening in their surroundings and react quickly to it. This is because they have some kind of nervous system. As a result, they can avoid danger and search for food and shelter. When the weather changes or a natural disaster, such as a fire or a flood, occurs, they may be able to move to a better place. Consequently, they have a better chance of survival. Animals can also adapt (change) to varying conditions more quickly. This ability has led to the great variety of animals and occurred during the process of evolution. (See Charles Darwin - origin of species theory)

There is much greater variety of animals than there is of plants. Biologists know of nearly a million different species (kinds) of animals, but only a third as many plants. Animals vary from the tiny one-celled amoeba, which can only be seen clearly under a microscope, to the huge blue whale, which may weigh 150 tons and measure 100 feet in length. Animals also live in almost every part of the world, from ocean deeps to high mountains.

But, in spite of this variety, most animals have similar features to some other animals. Biologists use such similarities as the basis on which to classify animals into groups. The closer they are related - the more similar they are - the closer is the grouping. In this way, a number of species may be grouped into a single genus, several of which make up a family. Families are themselves grouped into orders. A number of orders make a class, and several classes comprise a phylum. The 20-odd phyla are the principal groups that make up the animal kingdom..

By far the biggest of these in terms of the number of species is the phylum Arthropoda, the arthropods. This includes all the insects, crustaceans, spiders, scorpions, centipedes and millipedes. These groups are themselves classes within the phylum. Insects alone number over 800,000 species - more than three-quarters of all the known species of animals. Another important phylum is Mollusca, the molluscs. Most of these creatures have shells - examples include snails, clams, limpets, oysters' and mussels. But some molluscs, such as the squid and octopus, have entirely soft bodies, with no shells.

Kingdom Animal: facts for kids (click to increase)

Protochordata – animal facts for kids: Chordates that have no true brain and no braincase or backbone. They lack a heart and the type of kidney typical of vertebrates. Examples are the sea-squirts, lancelets and acorn worms.

Cyclostomata: Vertebrate chordates with an endo-skeleton of cartilage. They have no jaws and lack scales and bones. Examples are the lampreys, hag fishes and slime hags.

Elasmobranchii: Fishes with well-developed jaws. They have an endoskeleton made of cartilage; bone is entirely lacking. The skin is covered with horny, teeth-like scales.

Choanichthyes: Fishes with internal nostrils. Their paired fins have fleshy lobes. Examples are the coela-canth and lung fishes.

Actinopterygii – animal facts for kids: Ray-finned fishes with well-developed jaws. They have an endoskeleton made almost entirely of bone.

Amphibia: Cold-blooded vertebrate animals that usually need to return to the water to breed. Except in some limbless forms, they lack scales. They usually have lungs and a moist skin through which they can breathe. Examples are frogs, toads, newts and salamanders.

Reptilia – animal facts for kids: Cold-blooded vertebrates fitted for life on land. The skin is dry and covered in scales. They have lungs and show an advance on amphibians in laying shelled eggs which hatch on land. Examples are crocodiles, snakes, turtles and lizards.

Aves – animal facts for kids: Warm-blooded vertebrates that have feathers. Like most reptiles they lay shelled eggs. Another reptilian characteristic is the presence of scales on the legs and feet. The fore-limbs are modified as wings.

Mammalia: Warm-blooded vertebrates that have hair. The young are nourished with milk which is provided by milk or mammary glands. Except for the monotremes which lay eggs, mammals bear their young alive.

Monotremata: The egg-laying mammals. Examples are the platypus and spiny ant-eater. Neither animal has teeth.

Marsupialia: The pouched mammals. These bear their young alive but in a small, relatively unformed state. The female has a pouch on the lower part of the abdomen in which the young are carried and suckled until they are able to fend for themselves. Examples are the kangaroos, wallabies, koalas and opossums.

Placentalia – animal facts for kids: Mammals in which the young during their early development are connected to the mother by a 'plate' of tissue - the placenta. This passes on food, oxygen and chemicals to the embryo. The young are born at a more advanced stage than in other mammals. Examples are the rodents, cats, dogs, horses, sheep, monkeys, apes and man.

Perhaps the most varied and most important phylum is the Chordata, the chordates. What distinguishes them from all other animals is the hollow nerve cord that extends the length of their backs. They also have some kind of supporting rod of elastic material. In the more primitive chordates, this is a simple notochord, but the vertebrates - the most important group of chordates - all have backbones.

The vertebrates are the most advanced and most successful of all the animals. They include the fishes, amphibians, reptiles, birds and mammals. The mammals are the most advanced of the vertebrates, and the most advanced mammal is man himself.

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