Phylum Acanthocephala
Thorny-Headed Worms
Phylum Annelida
Annelid Worms
Phylum Arthropoda
Crabs, Insects, Shrimp & Spiders
Phylum Brachiopoda
Lamp Shells
Phylum Chaetognatha
Arrow Worms
Phylum Chordata
Phylum Cnidaria
Hydras & Jellyfish
Phylum Ctenophora
Comb Jellies
Phylum Cycliophora
Phylum Echinodermata
Sea Cucumbers, Sea Urchins & Sea Stars
Phylum Echiura
Spoon Worms
Phylum Ectoprocta
Moss Animals
Phylum Entoprocta
Goblet Worms
Phylum Gastrotricha
Phylum Gnathostomulida
Jaw Worms
Phylum Hemichordata
Acorn Worms
Phylum Kinorhyncha
Mud Dragons
Phylum Loricifera
Phylum Mesozoa
Phylum Mollusca
Clams, Octopi, Snails & Squid
Phylum Nemata
Phylum Nematomorpha
Horsehair Worms
Phylum Nemertinea
Ribbon Worms
Phylum Onychophora
Velvet Worms
Phylum Orthonectida
Phylum Phoronida
Horseshoe Worms
Phylum Placozoa
Phylum Platyhelminthes
Phylum Porifera
Phylum Priapulida
Priapus Worms
Phylum Rhombozoa
Phylum Rotifera
Phylum Sipuncula
Peanut Worms
Phylum Tardigrada
Water Bears

All animals are members of the Kingdom Animalia. All members of Kingdom Animalia are multicellular, and all are heterotrophs (that is, they rely directly or indirectly on other organisms for their nourishment). Most ingest food and digest it in an internal cavity.

Animal cells lack the rigid cell walls that characterize plant cells. The bodies of animals (all except sponges) are made up of cells organized into tissues, each tissue specialized to some degree to perform specific functions. In most, tissues are organized into even more specialized organs. Most animals are capable of complex and relatively rapid movement compared to plants and other organisms. Most reproduce sexually, by means of differentiated eggs and sperm. Most animals are diploid, meaning that the cells of adults contain two copies of the genetic material. The development of most animals is characterized by distinctive stages, including a zygote, formed by the product of the first few division of cells following fertilization; a blastula, which is a hollow ball of cells formed by the developing zygote; and a gastrula, which is formed when the blastula folds in on itself to form a double-walled structure with an opening to the outside, the blastopore.

Somewhere around 9 or 10 million species of animals inhabit the earth; the exact number is not known and even our estimates are very rough. Animals range in size from no more than a few cells to organisms weighing many tons, such as blue whales and giant squid. Most animals inhabit the seas, with fewer in fresh water and even fewer on land.

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Database Last Updated: 09 Jan 2009

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