Animals are eukaryotic organisms with many cells. They do not use light to get energy as plants do. The study of animals is called zoology.^[1][2] Animals use different ways to get energy from other living things. They usually eat other living things, but some are parasites or have photosynthetic protists as symbionts.

Plants are also multicellular eukaryotic organisms, but 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.

Grouping animals |

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.

Life styles |

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.^[3] 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 |

Animals Temporal range: Cryogenian – Present fossil range 670–0 mya
Scientific classification
(unranked):	Unikonta
(unranked):	Obazoa
(unranked):	Opisthokonta
(unranked):	Holozoa
(unranked):	Filozoa
Kingdom:	Animalia Linnaeus, 1758
Phyla
List of animal phyla Porifera Subkingdom Eumetazoa Ctenophora Placozoa Cnidaria †Trilobozoa Bilateria (unranked) Xenacoelomorpha †Proarticulata Nephrozoa (unranked) Superphylum Deuterostomia Echinodermata Hemichordata Chordata Protostomia (unranked) Superphylum Ecdysozoa Nematoda Nematomorpha Kinorhyncha Loricifera Priapulida Onychophora Arthropoda Tardigrada Spiralia (unranked) Gnathifera (unranked) Gnathostomulida Chaetognatha Rotifera Mesozoa (unranked) Dicyemida Monoblastozoa Orthonectida Rouphozoa (unranked) Gastrotricha Platyhelminthes Superphylum Lophotrochozoa Annelida Bryozoa Brachiopoda Cycliophora Entoprocta Mollusca Nemertea Phoronida
Synonyms
Metazoa

Wikispecies has information on: Animalia.

• List of animal phyla

References |

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