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Biodiversity Information

Composition of the Earth's Biodiversity

 Type of Organism Number of Described Species (%) Estimated Number of Species (%)*
Arthropods 1,065,000 (61%) 8,900,000 (65%)
Land plants 270,000 (15%) 320,000 (2%)
Protoctists 80,000 (5%) 600,000 (4%)
Fungi 72,000 (4%) 1,500,000 (11%)
Mollusks 70,000 (4%) 200,000 (1%)
Chordates 45,000 (3%) 50,000 (<1%)
Nematodes 25,000 (1%) 400,000 (3%)
Bacteria 4,000 (<1%) 1,000,000 (7%)
Viruses 4,000 (<1%) 400,000 (3%)
Other 115,00 (7%) 250,000 (2%)
Total 1,750,000 (100%) 13,620,000 (98%)

*Species estimates are working estimates. Percentages do not add up to 100% due to rounding

Arthropods - Invertebrates that have jointed limbs and segmented bodies covered by an exoskeleton, or outside shell. Includes crustaceans, insects, centipedes, millipedes, and spiders.

Land plants - Refers to mosses, liverworts, ferns and seed plants.

Protoctists - Neither animals, plants, fungi, or prokaryotes. Comprised of eukaryotic microorganisms and their immediate descendants, all nucleated algae (including the seaweeds), undulipodiated (flagellated) water molds, the slime molds and slime nets, and the protozoa.

Fungi - Lacking chlorophyll fungi feed on decaying matter or living organisms. Most fungi reproduce by forming spores, and they usually have cell walls that contain chitin or cellulose. Includes mildews, molds, mushrooms, plant rusts, and slime molds.

Mollusks - Live in aquatic or moist environments. Most mollusks have a hard shell enclosing a soft body. All mollusks have a mantle (a fleshy extension of the body wall) that hangs down on each side of the visceral mass (main bulk of the body). Includes oysters, mussels, clams, snails, slugs, limpets, squids, cuttlefish, and octopuses.

Chordates - Defined by the presence of three features: 1) single dorsal nerve chord, 2) a cartilaginous rod, the notochord, which forms dorsal to the primitive gut in the early embryo, and 3) the presence, at some stage in the life cycle, of gill slits in the pharynx or throat. Includes all mammals, birds, amphibians, reptiles, and vertebrate fish.

Nematodes - Round, tapered, thin worms; not segmented.

Bacteria - Refers to Archea and Eubacteria, simple, unicellular organisms.

Viruses - Parasitic, self-replicating, nucleic acid entities.


Table Sources:
BSCS. 2000. Biofact: Biodiversity Update. The Natural Selection. Fall: 11.
United Nations Environment Programme. 1995. Global biodiversity assessment. Cambridge, UK: Cambridge University Press.
Definition Sources:
Margulis, Lynn and Karlene Schwartz. 1982. Five Kingdoms. USA; W.H. Freeman and Company.
The World Book of Science Power. Vol 1. USA; The World Book, Inc. 1996.