Bilaterians
Bilaterians (pronunciation: /biˈlatərēən/) are a group of animals that have bilateral symmetry, meaning they have a front and back end, as well as an upside and downside, and therefore a left and a right side that are mirror images of each other.
Etymology
The term "Bilaterian" comes from the Latin bi- meaning "two" and latus meaning "side".
Characteristics
Bilaterians are characterized by their bilateral symmetry, a key development in animal evolution. This symmetry allows for streamlined and directional movement. Most bilaterians have a one-way digestive system, with a mouth at one end and an anus at the other.
Classification
Bilaterians include the majority of phyla, from arthropods to mammals. They are classified under the Kingdom Animalia, and are further divided into three major groups: deuterostomes, ecdysozoans, and lophotrochozoans.
Evolution
The evolution of bilaterians is a significant event in the history of life on Earth. The first bilaterians are thought to have appeared in the Ediacaran period, over 600 million years ago.
See Also
References
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