Question

What do you mean by body symmetry? Classify animals on the basis of it.

Answer 1

Symmetry:

1. The literal definition of symmetry is balanced proportions.
2. At a basic level of classification, true animals can be broadly classified into three groups based on the type of symmetry in their body.
3. These three groups of organisms are radially symmetrical, bilaterally symmetrical, and asymmetrical.

Radially symmetrical organisms:

1. It is a type of symmetry where any radial plane that passes through the centre of the organisms can divide it into two equal halves.
2. The symmetry is only visible for the morphological features and not anatomically.
3. Radial symmetry is found in cnidarians (these include jelly fish, sea anemones and corals) and echinoderms (these include sea urchins, brittle stars and sea stars).

Bilaterally symmetrical organisms:

1. It is a type of symmetry where only radial plane that passes through the centre of the organisms can divide it into two equal halves.
2. The symmetry is only visible for the morphological features and not anatomically.
3. Bilaterally symmetry is found in flatworms, common worms (also known as ribbon worms), clams, snails, octopus, crustaceans, insects, spiders, sea stars, sea urchins, and vertebrates.

Asymmetrical organisms:

1. It is a type of symmetry where no radial plane that passes through the centre of the organisms can divide it into two equal halves.
2. The symmetry is neither visible for the morphological features and nor anatomically.
3. Asymmetrical symmetry is found in snails, flounders and hermit crabs.