The simplest cephalization occurs in ____.

A) sea anemones
B) planarian flatworms
C) octopuses
D) vertebrates
E) grasshoppers

Planarian flatworms have the simplest form of cephalization, with a rudimentary brain and nerve cords running along the length of their body. They have a concentration of sensory organs at the head end of their body, indicating a basic form of sensory processing and coordination. Sea anemones, although also having a concentration of sensory organs, do not have a central nervous system or brain. Octopuses have a highly developed nervous system and complex cephalization, while vertebrates have a well-developed brain and vertebral column. Grasshoppers have a rudimentary nervous system and some cephalization, but not as developed as that of planarian flatworms.