EVERYDAY SCIENCE

Detailed explanation-1: -Most animals are bilaterally symmetrical with a line of symmetry dividing their body into left and right sides along with a “head” and “tail” in addition to a top and bottom. Only sponges (phylum Porifera) have asymmetrical body plans.

Detailed explanation-2: -Bilateral symmetry is characteristic of the vast majority of animals, including insects, fishes, amphibians, reptiles, birds, mammals, and most crustaceans.

Detailed explanation-3: -In this paper, the terms cylindrical and radial will be used as synonyms because in the context it makes no substantial difference. More than 99 % of animal species are bilaterally symmetrical.

Detailed explanation-4: -Examples of animals that possess bilateral symmetry are: flatworms, common worms ("ribbon worms"), clams, snails, octopuses, crustaceans, insects, spiders, brachiopods, sea stars, sea urchins, and vertebrates.

Detailed explanation-5: -Having bilaterally symmetrical bodies (the same on both sides along an axis) permit them to propel forward in a straight line. In evolutionary history, animals that moved quickly and efficiently from point A to point B would have been more successful and selected for than those who were ineffective at locomoting.