Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
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.