Dichotomous Key

From Wikibooks, open books for an open world
Jump to: navigation, search

This e-book can help with the identification of unknown organisms. The method adopted uses mostly a dichotomous key based on two choices, which is either in written format or pictographic, or both. For convenience, there may be polytomous sections within the book.

A written dichotomous key presents the reader with two statements that describe certain characteristics. The statements should be mutually exclusive for the key to work efficiently. For example, 'it is either red or it isn't'. On selecting one, the reader is presented with the next couplet choice in the key and so on - to eventually arrive at an identification. This key uses hyperlinks to navigate.

Classification with keys[edit]

Animal diversity October 2007 for thumbnail.jpg

Taxonomic systems are based on similar characteristics or increasingly on DNA analysis. The systems attempt to model the natural order, thus helping research by classifying different organisms. Taxonomic systems vary, but the following system has been found useful:

  • Domain
  • Kingdom
  • Phylum(called Division in plant
  • Class
  • Order
  • Family
  • Genus
  • Species

There are many sub units in use.

Keys usually start with a first selection from the following:

  • Plantae - Plants. Typically multicellular, sessile organisms. Their cells have walls composed of cellulose. They are autotrophs, and photosynthesize (with exceptions).
  • Animalia- Animals. Typically multicellilar, motile organisms. They lack rigid cell walls and are heterotrophic (with exceptions).
  • Protista - (A contested group of around 40 phyla of eukaryotic organisms) Typically simple, eukaryotic unicellular microorganisms or multicellular microorganisms without specialized tissues.
  • Fungi - Include yeast and molds. Typically eukaryotic, multicellular organisms. Like plants, they are sessile, but unlike plants they lack chloroplasts and are heterotrophic (with exceptions).
  • Bacteria - Ubiquitous, single-celled prokaryotes a few microns in size, with varying morphology.
  • Archaea - Relatively small group of single-celled prokaryotes more closely related to the eukaryotes than to the bacteria.

How the key works[edit]

  1. Go to start
  2. Use choices given to arrive at the lowest possible level
  3. Organism is identified as much as possible


If the description at each level does not appear accurate then back up to some earlier couplet and start over, questioning each decision more carefully. Finally, a verification step is important by comparing the specimen with any further details available including description,photographs and other reference. The habitat and location where the sample was collected is useful for plants. If the description and other information satisfactorily confer, then a correct identification is possible.

Start Here[edit]

Which Kingdom does it belong to?

Animalia[edit]

How many legs does it have

Plantae[edit]

What kind of plant is it?

No legs[edit]

What kind of animal is it?

2 Legs[edit]

What kind of animal is it?

4 Legs[edit]

What kind of animal is it?

Many legs[edit]

What kind of animal is it?

  • Starfish
  • Spider (Aranea), also Amblypygi, Solifugae, and Pantopoda (sea spiders)
  • Tick
  • Scorpion (Scorpiones), also Palpigradi, Amblypygi, Solifugae, Thelyphonida, Schizomida, and maybe Pseudoscorpionida just in case
  • Centipede
  • Millipede
  • Shrimp (Dendrobranchiata & Caridea), also Cumacea, Stomatopoda, and Stenopodidea (just in case)
  • Krill
  • Pillbug
  • Lobster or Crayfish (Astacidea) also achelata
  • Crab (Brachyura) also anomura (hermit crabs)
  • Insect

Fish[edit]

What kind of fish is it?

(Osteichthyes): Actinopterygii & Sarcopterygii, but also lampreys (Myxini) and hagfish (Petromyzontida)

Bird[edit]

What kind of bird is it?

Insect[edit]

What kind of insect is it?

Mammal[edit]

What kind of mammal is it?

Mammalia

Lizard[edit]

What kind of lizard is it?

Shark[edit]

  • Shark: Upper jaws not fused to skull; Has only one anal/urogenital opening; Has many sharp, replaceable teeth; Gill covering absent.
  • Chimaera: Upper jaws are fused with skull; has separate anal and urogenital openings; Only three pairs of large, permanent grinding tooth plates; Has a gill covering similar to that of bony fishes.

The keys in Wikibooks are still under development. A raw list is given below: