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Basic Facts

Basic Facts listed for each phylum handily group organisms' taxonomy, structure, and function, in a concise format for ease of reference.


Kingdom Protista: Single-Celled Organisms
  Taxonomic level: kingdom Protista; grade of construction: in effect, single autonomous cells; symmetry: variable; type of gut: none; type of body cavity other than gut: none; segmentation: none; circulatory system: none; nervous system: none; excretion: diffusion from cell surface.

Other features: autonomous single cells, reproducing by fission.

Number of species: over 30,000

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Phylum Porifera: Sponges, Simplest of Animals
Taxonomic level: phylum Porifera; grade of construction: cellular, with no distinct tissues or organs; symmetry: variable; type of gut: none; type of body cavity other than gut: none; segmentation: none; circulatory system: none; nervous system: none; excretion: diffusion from cell surface.

Other features: flagellated cells called choanocytes drive water through pores and cavities.

Number of species: 5,000

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Phylum Cnidaria: Hydrozoans, Jellyfish, Anemones, and Corals
Taxonomic level: phylum Cnidaria; grade of construction: two tissue layers; symmetry: radial; type of gut: blind gut; type of body cavity other than gut: none; segmentation: none; circulatory system: none; nervous system: network of nerve cells; excretion: diffusion from cell surface.

Other features: two basic stages—sessile polyp and swimming medusa, both tentaculate; includes anemones, corals, sea whips.

Number of species: 9,000

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Phylum Platyhelminthes: Flatworms
Taxonomic level: phylum Platyhelminthes; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: blind; type of body cavity other than gut: none; segmentation: absent; circulatory system: none; nervous system: small bundles of nerves (ganglia), two ventral nerve cords; excretion: excretory organs in many species.

Other features: flattened free-living worms, often with tubular pharynx to gather food; also, many parasitic species; representatives include the common freshwater planaria and the tapeworms.

Number of species: 12,000

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Phylum Nemertea: Ribbon Worms
Taxonomic level: phylum Nemertea; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete, with anus; type of body cavity other than gut: rhynchocoel surrounding proboscis; segmentation: absent; circulatory system: present; nervous system: small bundles of nerves (ganglia), two nerve cords; excretion: excretory organs in many species.

Other features: elongate free-living worms, with complete gut; carnivorous, using barbed proboscis to kill prey.

Number of species: greater than 800

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Phylum Nematoda: The Roundworms
Taxonomic level: phylum Nematoda; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete; type of body cavity other than gut: pseudocoel; segmentation: absent; circulatory system: present; nervous system: small bundles of nerves (ganglia), two nerve cords; excretion: special excretory cells.

Other features: small free-living and parasitic worms with only longitudinal muscles, circular in cross section; covered by cuticle; both free-living and parasitic.

Number of species: 12,000

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Phylum Annelida: Segmented Worms
Taxonomic level: phylum Annelida; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete with anus; type of body cavity other than gut: coelom; segmentation: present; circulatory system: closed system; nervous system: brain, with nerve cords and bundles (ganglia); excretion: excretory organs in most segments.

Other features: segmented worms, with great diversity of head and locomotory appendages; includes earthworm, sandworm, and lugworm.

Number of species: 12,000

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Phylum Sipuncula: Peanut Worms
Taxonomic level: phylum Sipuncula; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete with anus; type of body cavity other than gut: coelom; segmentation: absent; circulatory system: large coelomic cavity bathes most tissues; nervous system: brain with single ventral nerve cord, with branches; excretion: paired organs.

Other features: worm shaped, living in sediment and among rocks, feeding on sediment with protrusible organ called an introvert.

Number of species: about 300

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Phylum Ponogonophora: Gutless Wonders
Taxonomic level: phylum (might properly belong within the Annelida) Pogonophora; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: none; type of body cavity other than gut: coelom in several sections; segmentation: present in one region; circulatory system: dorsal and ventral blood vessels, with part of the dorsal vessel muscularized into a heart; nervous system: brain with rudimentary nerve cords; excretion: paired organs.

Other features: solitary worm-shaped individuals with no gut; rely upon symbiotic bacteria for nutrition.

Number of species; about 100

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Phylum Mollusca: Shelled Invertebrates (Mostly)
Taxonomic level: phylum Mollusca; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete, with anus; type of body cavity other than gut: coelom; segmentation: absent; circulatory system: usually open to large coelomic cavity; nervous system: brain, with nerve cords and bundles (ganglia), brain very well developed in squids and relatives; excretion: excretory organs.

Other features: typically externally shelled, mantle secretes shell; respires with ctenidium; includes clams, snails, squids, octopus.

Number of species: more than 100,000

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Phylum Arthropoda: Jointed Appendages
Taxonomic level: phylum Arthropoda; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete with anus; type of body cavity other than gut: coelom; segmentation: present; circulatory system: usually open to large coelomic cavity; nervous system: brain, with nerve cords and bundles (ganglia), compound eyes; excretion: excretory organs.

Other features: external cuticle, jointed appendages; includes horseshoe crabs, shrimp, crabs, sow bugs, insects.

Number of species: over one million

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Phylum Bryozoa: Moss Animals
Taxonomic level: phylum Bryozoa; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete; type of body cavity other than gut: coelom, usually reduced; segmentation: absent; circulatory system: absent; nervous system: single ganglion with nerves branching throughout zooid; excretion: no special structures.

Other features: colonial invertebrates, with small individuals (zooids) feeding with lophophore, growing in sheets or erect colonies; a colonial nervous system allows coordination of zooids.

Number of species: about 4,000

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Phylum Brachiopoda: Lingulas and Lampshells
Taxonomic level: phylum Brachiopoda; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete; type of body cavity other than gut: coelom, in two sections; segmentation: absent; circulatory system: heart with blood vessels; nervous system: rudimentary, but animals respond to light; excretion: no special structures.

Other features: solitary individuals with two valves, attached to bottom with pedicle, feed with ciliated lophophore.

Number of species: about 300

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Phylum Phoronida: Wormlike Animals with a Lophophore
Taxonomic level: phylum Phoronida; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete; type of body cavity other than gut: coelom in several sections; segmentation: absent; circulatory system: blood vessels moving fluid with peristaltic action; nervous system: rudimentary, but giant neurons extend for the length of the animal to allow instant shortening; excretion: possible presence of organs of excretion.

Other features: solitary individuals, wormlike, living in vertical tubes with lophophore protruding into water above.

Number of species: approximately 10

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Phylum Echinodermata: Animals with Fivefold Symmetry
Taxonomic level: phylum Echinodermata; grade of construction: organs derived from three tissue layers; symmetry: radial, sometimes combined with bilateral; type of gut: blind sac with very reduced anus, or complete with anus; type of body cavity other than gut: coelom; segmentation: none; circulatory system: usually open to large coelomic cavity; nervous system: major nerves extending from nerve ring, no brain; excretion: diffusion.

Other features: A spiny skin enclosed an internal skeleton of interlocking calcium carbonate plates; feeding and locomotion on tube feet connected to water vascular system; includes starfish or sea stars, sea cucumbers, sea urchins.

Number of species: approximately 6,000

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Phylum Chordata: The Sea Squirts
Taxonomic level: Subphylum Urochordata; grade of construction: organs derived from three tissue layers; symmetry: bilateral; type of gut: complete, with anus; type of body cavity other than gut: coelom; segmentation: none; circulatory system: heart with vessels; nervous system: brain with nerve cords; excretion: diffusion.

Other features: benthic sea squirts have a barrel-shaped body, with incoming and outgoing siphons; tadpole larvae have features allying this group with vertebrates.

Number of species: about 1,200

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