In which type of animals is a reflex action the most basic type of response?
 

A reflex action is an automatic, involuntary response to a stimulus. 

In lower animals, such as worms, insects, and fish, reflex actions are the most basic type of response to stimuli in the environment. This is because these animals have less complex nervous systems, with fewer interneurons and less processing power than higher animals.

In higher animals, including mammals like humans, reflex actions are still important but are not the most basic type of response. Higher animals have more complex nervous systems that allow for more sophisticated types of behavior, such as learning, decision-making, and voluntary movements. However, reflex actions are still important for survival and can occur even in the absence of conscious awareness. For example, pulling your hand away from a hot stove is a reflex action that occurs before you are consciously aware of the pain.