What is the difference between the structure of the nervous system of fish and the nervous system of the stag beetle?

The stag beetle belongs to invertebrates of the Arthropod type and the Insects class. These animals have a nodal type of nervous system. It consists of a periopharyngeal ganglion and three large ganglia in each segment of the chest. Nerves extend from the nerve nodes to all organs.
Fish are chordates, their nervous system is formed from the neural tube of the embryo and is therefore called the tubular nervous system. In fish, it consists of the brain and spinal cord, as well as numerous nerves.