A prominent evolutionary feature seen in higher forms of Kingdom Animalia is the development of a complex:
As animals evolved to actively search for food, avoid predators, and find mates, they required advanced bodily coordination. The NCERT textbook notes that higher forms of Kingdom Animalia show extraordinary elaboration and development of complex 'sensory and neuromotor mechanisms'. This encompasses everything from simple nerve nets in lower animals to the highly advanced brain and sensory organs found in vertebrates.
Ref: NCERT Class 11 Biology > Chapter 2: Biological Classification > 2.5 Kingdom Animalia