Evolution of nervous systems
Jellyfish, comb jellies, and related animals have diffuse nerve nets rather than a central nervous system. In most jellyfish the nerve net is spread more or less evenly across the body; in comb jellies it is concentrated near the mouth. The nerve nets consist of sensory neurons that pick up chemical, tactile, and visual signals, motor neurons that can activate contractions of the body wall, and intermediate neurons that detect patterns of activity in the sensory neurons and send signals to groups of motor neurons as a result. In some cases groups of intermediate neurons are clustered into discrete ganglia.
Sea turtle
Sea turtles' limbs and brains have evolved to adapt to their diets. One of the main things sea turtles consume is jellyfish and the use of their limbs to hold, swipe, and forage their food has helped them eat more efficiently. Originally sea turtles' limbs have evolved for locomotion but now they have evolved to aid them in the ability to get food. In addition to the evolution of limbs, sea turtles' brains have also evolved. The frontal cortex of a sea turtle's brain was not very developed. This underdevelopment caused the sea turtles to not be able to learn from their surroundings.