What is the difference between the nervous system of crayfish and the nervous system of an earthworm?

The nervous systems of annelids such as earthworms and crayfish are nodal systems. They are represented by the periopharyngeal nerve ring and the abdominal nerve cord.

But cancer has more complex behavior, it has senses:

– organs of vision – a pair of compound eyes;

– organs of touch – long antennae;

– organs of smell and balance – short antennae.

These features require a more developed nervous system. And therefore, in cancer, the supraopharyngeal ganglion is much larger than the subpharyngeal ganglion.