Classification of Animal Kingdom - Practice Questions & MCQ

Body Symmetry:

The general form of the body is called the symmetry. Animals can be  divided as per the following three types of body symmetry:

• Asymmetrical: Such animals cannot be divided into equal halves along any plane, for example, sponges.
• Radially symmetrical: The body parts are arranged around the central axis such that the body has a top and bottom surface but no left, or right or front or back. Such a body can be equally divided into two equal halves along any plane. For example, coelenterates and ctenophores.
• Bilateral symmetrical: Such animals can be divided into two equal halves along any one plane, that is, either transversely or longitudinally. For example, annelids, arthropods, and vertebrates.

Germ Layers:

• During the gastrulation stage of embryo development, the cells of an embryo can be arranged in the form of germ layers and each germ layer is capable of giving rise to specific tissues or organs. Based on the number of germ layers, the animals can be of two types:
• Diploblastic animals: Such animals develop two germ layers as inner endoderm and outer ectoderm. There is a non-cellular layer present between endoderm and ectoderm called the mesoglea. Mesoglea is completely undifferentiated layer. For example, coelenterates. 
• Triploblastic animals: Such animals develop three germ layers as innermost endoderm, middle mesoderm and outer ectoderm.