Biology XI:4 Animal Kingdom (1 Basis of classification for Animalia

Basis of classification for Kingdom Animalia Basis of Classification Arrangement of cells (levels of organisation) Body symmetry Nature of coelom Patterns of digestive, circulatory, or reproductive systems are some of the features used to classify animals. Arrangement of cells in germ layer Presence or absence of notochord Levels of Organisation All members of Animalia are multicellular, but exhibit different levels of organisation. Symmetry Planes passing through the body dividing it into equal halves   Diploblastic and Triploblastic Organisation Diploblastic Organisation Cell arranged in two embryonic layers: Ectoderm (external) Endoderm (internal) Presence of an undifferentiated layer, i.e. mesoglea, in between two embryonic layers Example − coelenterates Triploblastic Organisation Cells arranged in three embryonic layers: Ectoderm (external) Mesoderm (middle) Endoderm (internal) Example − Platyhelminthes and chordates Coelom Coelom − Mesoderm-lined body cavity present in between body wall and gut wall Segmentation In some animals, body is externally and internally divided into segments with certain organs repeated serially. Example: EarthwormThe phenomenon of division of body of the earthworm into metameric segments is known as metamerism. Notochord It is a mesoderm derived rod-like structure, which is formed dorsally in some animals during embryonic development.