Editing Sipuncula (section)

===Nervous system===
[[File:Esquema do Sistema Nervoso de Sipuncula.png|thumb|Nervous system of Sipuncula]]
The nervous system consists of  dorsal cerebral ganglion, brain above the oesophagus and a nerve ring around the oesophagus, which links the brain with the single ventral nerve cord that runs the length of the body. Lateral nerves lead off this to innervate the muscles of the body wall.<ref name=Ruppert/>

In some species, there are simple light-sensitive [[ocelli]] associated with the brain. Two organs, likely functioning as a unit for [[Chemoreceptor|chemoreception]] are located near its anterior margin; the non-ciliated cerebral organ, which possesses [[Bipolar neuron|bipolar sensory cells]], and the nuchal organ, located posterior to the brain.<ref name=IZ/> Similar light-sensing tubes have been reported in the [[Fauveliopsidae|fauveliopsid]] annelids.<ref>{{cite journal|year=2011|author= Purschke, Günter|title=Sipunculid-like ocellar tubes in a polychaete, ''Fauveliopsis cf. adriatica'' (Annelida, Fauveliopsidae): implications for eye evolution| journal=Invertebrate Biology| volume=130 |issue=2 |pages=115–128|doi=10.1111/j.1744-7410.2011.00226.x}}</ref> In addition, all sipunculans have numerous sensory nerve endings on the body wall, especially at the forward end of the introvert which is used for exploring the surrounding environment.<ref name=IZ/>