WRI Content Archive

Please visit www.wri.org for the latest WRI resources & materials.

Relative number of described species in major taxa

Source: World Resources Institute, IUCN-The World Conservation Union, United Nations Environment Programme (UNEP) in consultation with the Food and Agriculture Organization (FAO) and the United Nations Education, Scientific and Cultural Organization (UNESCO). 1992. Global Biodiversity Strategy: Guidelines for action to save, study and use Earth's biotic wealth sustainably and equitably.

Placeholder image, please replace

Source: NASA Goddard Space Flight Center Image GOES-8 (Date: 01/01/1994)

Species Diversity and Classifications

Species diversity refers to the variety of living organisms on earth and has been variously estimated to be between 5 and 50 million or more, though only about 1.4 million have actually been described. Biologists classify life on earth into a widely accepted hierarchical system that reflects evolutionary relationships among organisms. In ascending order, the main categories or taxa, of living things are:

  • Species,
  • Genus,
  • Family,
  • Order,
  • Class,
  • Phylum,
  • Kingdom.
Humans, for example, are classified as follows: Animalia (Kingdom), Chordata (Phylum), Mammalia (Class), Primates (Order), Hominidae (Family), Homo (Genus), sapiens (Species). These last two designations, together referred to as the Latin binomial, are used to identify an organism, and distinguish it from any other.

In general, the higher the category ranking of an organism, the more ancient the evolutionary divergence. Thus, with Homo sapiens, it was more recently that the species became established than the genus, and more recently that the genus evolved than did the family (Hominidae), and so on up to the Kingdom level.

Most biologists recognize five kingdoms of organisms:
  • Prokaryotae (bacteria),
  • Protoctista (includes algae and protozoans),
  • Fungi (mushrooms, molds, and lichens),
  • Animalia (animals), and
  • Plantae (plants).

Relative Number of Species by Major Taxa

The following is an informal listing of the relative number of species by major taxa according to species type and number of described species. A good place to visit for more information is the Online Exhibit: Web Lift to any Taxon by the Museum of Paleontology of the University of California at Berkeley.
      Insecta
      751,000 described species

      Plantae (Multicellular Plants)
      248,428 described species

      Non-insect Arthropoda (Mites, Spiders, Crustaceans etc.)
      123,151 described species

      Mollusca (Mollusks)
      50,000 described species

      Fungi
      46,983 described species

      Protozoa
      30,800 described species

      Algae
      26,900 described species

      Pisces (Fish)
      19,056 described species

      Platyhelminthes (Flatworms)
      12,200 described species

      Nematoda (Roundworms)
      12,000 described species

      Annelida (Earthworms etc.)
      12,000 described species

      Aves (Birds)
      9,040 described species

      Coelenterata (Jellyfish, Corals, Comb Jellies)
      9,000 described species

      Reptilia (Reptiles)
      6,300 described species

      Echinodermata (Starfish, etc.)
      6,100 described species

      Porifera (Sponges)
      5,000 described species

      Monera (Bacteria, Blue-green Algae)
      4,760 described species

      Amphibia (Amphibians)
      4,184 described species

      Mammalia (Mammals)
      4,000 described species