Download Characteristics Used to Classify Animals

Characteristics Used to Classify Animals
Body plan
Symmetry
 Radial symmetry – Body can be divided equally along any plane, through a central axis
 Bilateral symmetry – Body can be divided equally only along one plane, through a central axis
 Asymmetry – Body has an irregular shape with no symmetry
Radial symmetry
Bilateral symmetry
Tissue layers
Developing embryos consist of layers of cells, called germ layers. These germ layers
eventually give rise to different tissues in the fully-formed embryo. Animals can be
classified on the basis of how many germ layers their embryos contain.
 Diploblastic – Contain two germ layers: endoderm and ectoderm.
o Endoderm gives rise to the outer covering of the organism.
o Ectoderm gives rise to some of the internal organs, and the lining of
the digestive tract.
 Triploblastic – Contain three germ layers: endoderm, mesoderm, and ectoderm.
o Mesoderm – Fills the space between the endoderm and ectoderm; gives rise to the
muscles and other internal organs.
Body cavity
A coelom is a fluid- or air-filled body cavity found between the digestive tract and outer body wall. It
forms entirely from tissue derived from the mesoderm. It suspends the organs and provides
cushioning.
 Coelomate – Contains a true coelom, whose inner and outer surface is composed entirely of
mesoderm.
 Acoelomate – Has no coelom.
 Pseudocoelomate – Has a body cavity, but it is not entirely composed of mesoderm (inner
surface is endoderm).
Segmentation
 Segmented organisms have a body divided into repetitive sections (segments).
Behaviour
Movement
 Sessile – Stationary; lives attached to one location.
o Many organisms with radial symmetry are sessile.
 Motile – Organism can move around its environment on its own. Requires a complex
nervous system to co-ordinate muscle action.
o Most organisms with bilateral symmetry are motile.
Reproduction
 Sexual reproduction – Two parents contribute genetic material to produce offspring.
o Internal fertilization – Gametes combine inside the body
o External fertilization – Gametes combine outside the body; typical of aquatic animals
 Asexual reproduction – One parent contributes genetic material to produce offspring.