Annelida
Annelids are a large invertebrate phylum, with over thousands of modern species such as ragworms, earthworms and leeches. The nervous system of Annelids typically consists of a primitive brain, or cerebral ganglion (a structure containing a number of nerve cell bodies) that originates and usually is located in the upper "head" region. The ventral nerve cord, is usually made up of a pair of cords that are bound together that runs the length of the body. The cord consists of lateral nerves and ganglia in each segment. It is connected to the ventral nerve cord by the circumpharyngeal connectives, which run down each side of the pharynx. It varies in thickness and changes into a ganglion in each segment, from which pairs of segmental nerves pass out to the body wall, muscles and gut.
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