Dichotomous Key/Animalia

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Dichotomous Key
Kingdom Animalia

Key to Animalia

  • 1: Single-celled organism.
  • 2: Multi-cellular organism.



Single cell protists

Glossary for this page
(all links are to Wikipedia articles)
Digestive cavity:
Radial symmetry: Circular symmetry where cutting planes produces roughly identical pieces
Bilateral symmetry: Symmetry where only one plane, called the sagittal plane, will divide an organism into roughly mirror image halves
Trochophore: A type of free-swimming ciliated planktonic marine larva
Lophophore: A feeding organ consisting of a ring of ciliated tentacles surrounding the mouth.
Segmentation: The division of body plans into a series of repetitive segments.


  • 3: Specialized cells absent, though different types of cells may be present. Digestive cavity absent. Muscles, nerves, and organs absent. Parazoa.
  • 4: Specialized cells present. Digestive cavity present. Muscles, nerves, and organs present in some form. True tissues organized into germ layers. Enterozoa.

3: Parazoa

4: Eumetazoa

  • 5: Hollow body cavity present. Radially symmetric body. Aquatic. Colonial or solitary. Respiration and excretion accomplished by diffusion.
  • 6: Body cavity not hollow. Radially or bilateral body symmetry. Aquatic, terrestrial or both. Mostly solitary.


  • Cnidaria: Cnidocytes present; Medusa and polyp form; Incomplete digestive system.
  • Ctenophora: Sticky prey-capturing colloblast cells present; Medusa form only; Complete digestive system.


  • Chordate: Possesses a notochord, a hollow dorsal nerve cord, pharyngeal slits, or an endostyle, for at least some period of its life cycle.
  • 7: Notochord, a hollow dorsal nerve cord, pharyngeal slits, and an endostyle absent during entire life cycle.


  • Echinoderm: Adults have radial symmetry. Inhabitants of salt water.
  • 8: Adults have bilateral symmetry. Inhabitants of fresh water, salt water, or dry land.


  • Ecdysozoa: Exoskeleton shed during life cycle.
  • 9: Exoskeleton absent, or not shed during life cycle.



Orthonectida, Rhombozoa, Acoelomorpha, Chaetognatha, Hemichordata, Xenoturbellida, Platyzoa, Lophotrochozoa