Question

cnidaria - shape of life
why did cnidarians mark a turning point for animal behavior?
they could survive on land
they had hard shells for protection
they developed lungs
they had tentacles that could sense and interact with the world

Explanation:

Cnidarians are aquatic animals. They do not have hard shells (unlike some mollusks), they do not have lungs (as they are simple in structure and gas exchange is through the body surface), and they cannot survive on land. Their tentacles have cnidocytes which can sense the environment and interact (e.g., capture prey).

Answer:

They had tentacles that could sense and interact with the world.