Topic- Basis of Classification
Description - Despite the differences in structures and forms of different animals, there are some common features among them which form the basis for animal classification. These features are -
- Arrangement of cells - cellular level, tissue level, organ level and organ system level (complete and incomplete)
- Body symmetry - Categorized under asymmetrical, radial and bilateral symmetry.
- Nature of coelom - Coelomates (presence of coelom), Acoelomates (absence of coelom) and Pseudocoelomates (false coelom)
- Germinal layers - Cells are arranged in three embryonic layers, external ectoderm, internal endoderm and a middle mesoderm . Organisms with only ectoderm and endoderm are called diploblastic and with all three layers are called triploblastic.
- Segmentation - The body possesses a serial repetition of body segments, called metameric segmentation.
- Notochord - Mesodermally derived rod-liked structures are formed during embryonic development in some animals, they are called chordates. Animals that do not form this structure are called non-chordates.
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