Question

why are they regarded as primitive organisms ​

Answer 1

Answer:

Since they can adapt to widest range of atmospheric conditions, so it is believed that when many of the animals would have gone extinct due to harsh atmospheric conditions they still had survived. They are believed to be on Earth back in the time when even Humans were not present on Earth

Explanation:

Answer 2

Answer:

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Primitive organisms are those which have ancient body designs and have not changed much. They have simpler body design and are also called lower organisms.