Balanced distribution of different parts of the body is called symmetry.
(i) Asymmetry: If the body of an animal is not divided into two equal parts along the center or axis, it is called asymmetric. For example – Snail (Pila globosa), Amoeba (Amoeba proteus), Spongilla (Spongilla proliferens), Sponge (Cliona celata) etc.
(ii) Bilaterally symmetrical: When the body of an animal is divided along the center into two equal parts, it is called bilaterally symmetrical. Their taxonomic level is Bilateria. Animals of the order Platyhelminthes, Arthropoda I Chordata are bilaterally symmetrical. For example, humans (Homo sapiens), cockroaches (Periplaneta americana), frogs (Duttaphrynus melanostictus), butterflies (Pieris brassicae), Inlish (Tenualosa ilisha), pigeons (Columba livia), liver worms (Fasciola hepatica) etc.
(iii) Biradial symmetrical: If the body of an animal is divided longitudinally along the axis to get two equal parts, it is called biradial symmetrical. In this case four equal parts are obtained as the cutting planes are at right angles. Such symmetry is called Tetramerous symmetry. Such as Anthozoa, Ctenophora, Ceoloplana etc.
(iv) Radial symmetrical: If the body of an animal is divided along the center to get more than two equal parts, it is called radial symmetry. Their taxonomic level is radiata. Such as Hydra (Hydra vulgaris), Jelly fish (Aurelia aurita), Sea anemone (Metridium dianthus), Sea snake (Astropecten auranciacus).
(v) Spherical symmetry: If the body of an animal is divided repeatedly along the center and two equal parts are obtained each time, it is called spherical symmetry. Like Volvox globactor, Radiolaria (Acrosphaera trepanata), Haliozoa (Gymnosphaera albida) etc.