Why Are Animals Mostly Symmetrical and Why Some Aren't?

Do you know the difference between a bilaterian and a cnidarian?

You may not have noticed this because it is so common, but most animals are symmetrical. This means that their right side and left side mirror each other to a good degree.

These types of animals are known as the bilaterians and they are separated into three further groups: the vertebrates, the mollusks, and the arthropods. All the animals in these categories are perfectly symmetrical (except for internal organs).

Some animals, however, called the cnidarians, have a different kind of symmetry or no symmetry at all. These are jellyfish, corals, and more. Jellyfish have radial symmetry and sponges have no symmetry whatsoever.

The reasons why these animals are so different are mysterious. Indeed, they are the result of thousands of years of evolution that led to their current shapes.

In this video, YouTuber Moth Light Media explains this large history so that you can fully understand how today's animals came to be. He even explains how the bilaterians came to be the most common type of animals and how they came to dominate land while cnidarians remained in the sea.

Have we piqued your curiosity yet? Then watch this video to learn all about bilaterians and cnidarians and their rich and fruitful history.

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