Classification of Animals

Phylum	Common Names/ Examples	No. of Species	Comments
The animal kingdom is usually divided into about 30 phyla, which differ enormously in size.
Acanthocephala	Spiny-headed worms	600	Gut parasites of vertebrates, usually of carnivores.
Annelida	Earthworms, leeches	8,900	Worms with a well-developed coelom, and the body divided up into a number of more or less similar segments. Terrestrial, freshwater or marine.
Arthropoda	Crustaceans, scopions, spiders, insects	>2,000,000	By far the largest animal phylum with more species than all the other phyla combined (more than 800,000 species of insects alone have been described, some zoologists there may be as many as 10 milliom). Arthropods are segmented animals with paired, jointed appendages on some or all of their body segments.
Brachiopoda	Lamp shells	335	Bottom-living marine animals with shells with two valves. They thrived during the Paleozoic era - more than 30,000 extinct species have been described.
Chaetognatha	Arrow worms	>100	Small, slender torpedo-shaped marine planktonic animals which are voracious carnivores.
Chordata	Mammala, birds, amphibians, reptiles, fish	45,000	The best known phylum of Animalia containing all the species which, in the minds of many, are considered 'animals'. Chordates are distinguished by (i) having the walls of their pharynx, at some stage in their life cycle, perforated by gill clefts; (ii) a hollow dorsal nerve cord; (iii) an axial cartilagenous rod, the notochord - lying immediately beneath the nerve chord. Most chordates have backbones and are called vertebrates, but two of three subphyla are small invertebrate groups.
Cnidaria	Coelenterates, hydra, corals	9,500	Nearly all marine. Radially symmetrical with tissues and organs, have stinging cells (nematocysts) on tentacles.
Ctenophora	Comb jellies, sea gooseberries	90	Aquatic, transparent.
Echinodermata	echinoderms, including starfish, sea urchins	6,000	Marine, mostly bottom-dwelling animals usually displaying five-fold symmetry. The fluid-filled tube feet are used for locomotion and feeding.
Echiura	Spoon worms	140	Unsegmented marine worms which burrow in marine deposits.
Ectoprocta	Ectoprocts	5,000	Small aquatic animals, mostly colonial.
Entoprocta	Entoprocts	150	Small marine animals, mostly sedentary, living in colonies attached to rocks, shells, algae or other animals.
Gastrotricha	Gastrotrichs	400	Aquatic microscopic animals with cilia on their bodies.
Gnasthostomulida	Jaw worms	80	Microscopic marine worms.
Hemichordata	Hemichordates	90	Small, soft-bodied animals that inhabit shallow u-shaped burrows in sandy or muddy sea bottoms.
Kinorhyncha	Kinorhynchs	150	Small worm-like marine animals.
Loricifera	Loriciferans	10	Tiny marine animals with abdomen covered by a girdle of spiny plates called a lorica.
Mesozoa	Mesozoans	50	Small, worm-like organisms.
Mollusca	Molluscs, including snails, clams, mussels	110,000	The second largest phylum of animals, molluscs live in aquatic or moist environments, are soft-bodied and are ususally protected by a calcareous shell that is secreted by a fold of the body wall called the mantle.
Nematoda	Nematodes or roundworms	>80,000	Unsegmented, more or less cylindrical worms which occur free-living in all types of environment, and also as parasites of plants and animals. It has been estimated that there may be as many as 1 million species of nematode in the world (ie vast numbers of undiscovered species). In terms of numbers of individuals, nematodes are the most abundant group of multicellular animals.
Nematomorpha	Horsehair worms, Gordian worms	240	Very long, thin worms which are parasitic in insects and crustaceans as juveniles, and free-living in water as adults.
Nemertina	Ribbon worms, proboscis worms	900	Characteristic feature is long, sensitive anterior proboscis, used to explore the environment and capture prey
Onychophora	Velvet worms	80	Soft-bodied, segmented animals with many paired but unjointed legs. Confined to humid tropics.
Pentastoma	Tongue worms	70	Parasitic worms in the respiratory passages of air-breathing vertebrates with a chitinous cuticle that is periodically moulted to allow growth.
Phoronida	Horeshoe worms	10	Marine worms with as many as 1,500 hollow tentacles. Live in tubes which they secrete and strengthen with sand or shell fragments.
Placozoa	trichoplax adhaerens	1	The only species in the phylum, this is the simplest animal known. No tissues, organs or symmetry.
Platyhelminthes	Flatworms, flukes, tapeworms	15,000	Ribbon-shaped and soft-bodied, the least complex of the animals that have heads.
Pogonophora	Beard worms	100	Extremely slender gutless, tube-living marine worms.
Porifera	Sponges	10,000	All aquatic, vast majority in sea-water, 150 in fresh water. No tissues, organs or symmetry.
Priapulida	Priapulids	10	Small carnivorous marine worms.
Rotifera	Rotifers or wheel animals	2,000	Aquatic microscopic animals with their anterior end modified into ciliary organs called corona, the beating of which resembles a rotating wheel.
Sipuncula	Peanut worms	>300	Unsegmented marine worms, live in crevices or are burrowing.
Tardigrada	Water bears	380	Minute animals which live in films of water around mosses and other low terrestrial features. Four pairs of stubby legs armed with terminal claws.

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Last updated: 2005-01-17