Final answer:
The first landmark of nervous system formation is exhibited by the fruit fly (Drosophila melanogaster), with the formation of the neural tube being a critical step in this process. The neural crest is associated with the development of the peripheral nervous system, and all nervous systems, regardless of species, govern similar behaviors.
Step-by-step explanation:
The animal that exhibits the first landmark of nervous system formation is a) Fruit fly (Drosophila melanogaster). In the fruit fly, the embryonic development of the nervous system begins with the formation of the neural tube. The neural tube is a key structure that eventually gives rise to the central nervous system, which includes the brain and spinal cord in vertebrates.
When we consider embryonic development, the neural crest plays a pivotal role in the development of the peripheral nervous system. The nervous system, whether in a fruit fly or a human, controls many of the same behaviors, from basic reflexes to complex behaviors such as finding food and mate selection. This is despite the vast differences in the number of neurons among these species.
The neural tube and neuraxis are fundamental structures in the development and arrangement of the mammalian nervous system, which is initially laid out along an anterior to posterior axis.