Animal facts for kids

Quick facts for kids Animals
Various animals
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia

Animals are eukaryotic organisms with many cells. They do not use light to get energy as plants do. Animals use different ways to get energy from other living things. They may eat other living things, though some are parasites or have photosynthetic protists as symbionts.

Most animals are mobile, meaning they can move around. Animals take in oxygen, and give out carbon dioxide. This cellular respiration is part of their metabolism (chemical working). In both these ways they are different from plants. Also, the cells of animals have different cell membranes to other eukaryotes like plants and fungi. The study of animals is called zoology.

Plants are also multicellular eukaryotic organisms, but live by using light, water and basic elements to make their tissues.

Grouping animals

Yellow-winged darter, Sympetrum flaveolum

There are many different types of animals. The common animals most people know are only about 3% of the animal kingdom. When biologists look at animals, they find things that certain animals have in common. They use this to group the animals in a biological classification. They think several million species exist but they have only identified about one million.

Animals can mainly be divided into two main groups: the invertebrates and the vertebrates. Vertebrates have a backbone, or spine; invertebrates do not.

Vertebrates are:

• fish (or 'fishes': both ways are correct)
• amphibians
• reptiles
• birds
• mammals

Some invertebrates are:

• insects
• spiders
• crustaceans
• molluscs (like a snail or squid)
• worms
• jellyfish

In scientific usage, humans are considered animals, in everyday nonscientific usage, humans are often not considered to be animals.

Numbers and habitats

The following table lists estimated numbers of described extant species for the animal groups with the largest numbers of species, along with their principal habitats (terrestrial, fresh water, and marine), and free-living or parasitic ways of life. Species estimates shown here are based on numbers described scientifically; much larger estimates have been calculated based on various means of prediction, and these can vary wildly. For instance, around 25,000–27,000 species of nematodes have been described, while published estimates of the total number of nematode species include 10,000–20,000; 500,000; 10 million; and 100 million. Using patterns within the taxonomic hierarchy, the total number of animal species—including those not yet described—was calculated to be about 7.77 million in 2011.

Phylum	Example	No. of Species	Land	Sea	Fresh water	Free- living	Parasitic
Annelids		17,000	Yes (soil)	Yes	1,750	Yes	400
Arthropods		1,257,000	1,000,000 (insects)	>40,000 (Malac- ostraca)	94,000	Yes	>45,000
Bryozoa		6,000		Yes	60-80	Yes
Chordates		65,000 45,000	23,000	13,000	18,000 9,000	Yes	40 (catfish)
Cnidaria		16,000		Yes	Yes (few)	Yes	>1,350 (Myxozoa)
Echinoderms		7,500		7,500		Yes
Molluscs		85,000 107,000	35,000	60,000	5,000 12,000	Yes	>5,600
Nematodes		25,000	Yes (soil)	4,000	2,000	11,000	14,000
Platyhelminthes		29,500	Yes	Yes	1,300	Yes	>40,000
Rotifers		2,000		>400	2,000	Yes
Sponges		10,800		Yes	200-300	Yes	Yes
Total number of described species as of 2013: 1,525,728

Life styles

In Gombe Stream National Park, male chimpanzees remain in their natal community while females disperse to other groups

The animal mode of nutrition is called heterotrophic because they get their food from other living organisms. Some animals eat only plants; they are called herbivores. Other animals eat only meat and are called carnivores. Animals that eat both plants and meat are called omnivores.

The environments animals live in vary greatly. By the process of evolution, animals adapt to the habitats they live in. A fish is adapted to its life in water and a spider is adapted to a life catching and eating insects. A mammal living on the savannahs of East Africa lives quite a different life from a dolphin or porpoise catching fish in the sea.

The fossil record of animals goes back about 600 million years to the Ediacaran period, or somewhat earlier. During the whole of this long time, animals have been constantly evolving, so that the animals alive on Earth today are very different from those on the edges of the sea-floor in the Ediacaran. The study of ancient life is called palaeontology.

Related pages

• List of animal phyla

Images for kids

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  Animals are unique in having the ball of cells of the early embryo (1) develop into a hollow ball or blastula (2).

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  Predators, such as this ultramarine flycatcher (Ficedula superciliaris), feed on other animals.

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  Hydrothermal vent mussels and shrimps

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  The blue whale is the largest animal that has ever lived.

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  Non-bilaterians include sponges (centre) and corals (background).

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  Ecdysis: a dragonfly has emerged from its dry exuviae and is expanding its wings. Like other arthropods, its body is divided into segments.

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  Spiral cleavage in a sea snail embryo

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  Jean-Baptiste de Lamarck led the creation of a modern classification of invertebrates, breaking up Linnaeus's "Vermes" into 9 phyla by 1809.

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  Sides of beef in a slaughterhouse

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  A gun dog retrieving a duck during a hunt

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  Artistic vision: Still Life with Lobster and Oysters by Alexander Coosemans, c. 1660

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  Dickinsonia costata from the Ediacaran biota (c. 635–542 mya) is one of the earliest animal species known.

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  Auroralumina attenboroughii, an Ediacaran predator (c. 560 mya)

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  Anomalocaris canadensis is one of the many animal species that emerged in the Cambrian explosion, starting some 539 million years ago, and found in the fossil beds of the Burgess shale.

See also

In Spanish: Animalia para niños