Nervous system
Nervous systems are found in most multicellular animals, but vary greatly in complexity. The only multicellular animals that have no nervous system at all are sponges, placozoans, and mesozoans, which have very simple body plans. The nervous systems of the radially symmetric organisms ctenophores (comb jellies) and cnidarians (which include anemones, hydras, corals and jellyfish) consist of a diffuse nerve net. All other animal species, with the exception of a few types of worm, have a nervous system containing a brain, a central cord (or two cords running in parallel), and nerves radiating from the brain and central cord. The size of the nervous system ranges from a few hundred cells in the simplest worms, to around 300 billion cells in African elephants.
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.