During the Cambrian explosion, the characteristics of animals that appeared include . During the Cambrian explosion, the characteristics of animals that appeared include . mammals that could climb trees swimming protostomes flying reptiles armored reptiles

Swimming protostomes

Explanation:

The Cambrian period is the geological time period which is known for the evolution of a large number of organisms.

During this period, the condition became favourable for the growth of life that is temperature became suitable, the evolution of oxygen and the rise in the sea level. A large number of species evolved during this period like segmented body organisms called arthropods and which lived in the shells like molluscs.

These organisms dominated the Earth and are considered protostomes on the basis of their growth pattern during organogenesis as their mouth is formed earlier than the anus.

Thus, swimming protostome is the correct answer.

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