Chondrichthyes
Chondrichthyes nervous system is composed of a small brain, 8-10 pairs of cranial nerves, and a spinal chord with spinal nerves. They have several sensory organs which provide information to be processed. Ampullae of Lorenzini are a network of small jelly filled pores called electroreceptors which help the fish sense electric fields in water. This aids in finding prey, navigation, and sensing temperature. The Lateral line system has modified epithelial cells located externally which sense motion, vibration, and pressure in the water around them. Most subspecies have large well-developed eyes. Also, they have very powerful nostrils and olfactory organs. Their inner ears consist of 3 large semicircular canals which aid in balance and orientation. Their sound detecting apparatus has limited range and is typically more powerful at lower frequencies. Some subspecies have electric organs which can be used for defense and predation. They have relatively simple brains with the forebrain not greatly enlarged. The structure and formation of myelin in their nervous systems are nearly identical to that of tetrapods, which has led evolutionary biologists to believe that Chondrichthyes were a cornerstone group in the evolutionary timeline of myelin development.
Scaly-foot gastropod
The nervous system is large, and the brain is a solid neural mass without ganglia. The nervous system is reduced in complexity and enlarged in size compared to other neomphaline taxa. As is typical of gastropods, the nervous system is composed of an anterior oesophageal nerve ring and two pairs of longitudinal nerve cords, the ventral pair innervating the foot and the dorsal pair forming a twist via streptoneury. The frontal part of the oesophageal nerve ring is large, connecting two lateral swellings. The huge fused neural mass is directly adjacent to, and passes through, the oeosophageal gland, where the bacteria are housed. There are large tentacular nerves projecting into the cephalic tentacles. The sensory organs of the scaly-foot gastropod include statocysts surrounded by the oesophageal gland, each statocyst with a single statolith. There are also sensory ctenidial bursicles on the tip of the gill filaments; these are known to be present in most vetigastropods, and are present some neomphalines.