Their nervous system consists of a nerve ring around the oesophagus, which functions as a brain, and a single ventral nerve cord that runs down the body. Their digestive system consists of a mouth, an oesophagus, an intestine which is looped into a a double helix, and an anus. The mouth is surrounded by tentacles which are are used to collect organic detritus and probably also function as gills.
Food particles are gathered with the tentacles and then either the entire introvert is withdrawn into the trunk and the food particles eaten, or cilia on the tentacles transfer the particles along tracts into the mouth.
Sipunculans reproduce asexually and sexually, although asexual reproduction is uncommon. Fertilization takes placein the water. Some species hatch directly into the adult form, others have a larval stage, which metamorphoses into the adult after anything from a day to a month, depending on the species.