Primitive organisms are also known as

Organisms undergo evolution, which the passage of time and accumulate changes in their body design resulting in marked differences between the evolved ones and their ancestors.

On the basis of evolution we classify organisms as primitive and advanced organisms.

Organisms that look similar to their ancestral body design are called primitive or lower organisms.

Whereas, organisms that show complex body design are called advanced or higher organisms.

Hence, option B is the correct answer.