# Streptoneury

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**Streptoneury** or **chiastoneury** is a [plesiomorphic](/source/Symplesiomorphy) condition present in all [gastropods](/source/Gastropoda) which is a result of an evolutionary event called [torsion](/source/Torsion_(gastropod)) in which the intestines, heart, [nephridia](/source/Nephridium), gills, and nerve cords "twist" causing some organs to migrate from the animal's left to its right in order to accommodate the relocation of the [mantle cavity](/source/Mantle_(mollusc)) close to the animal's head. Specifically, streptoneury is the crossing of the cerebrovisceral [connectives](/source/Connective_fiber) caused by this torsion.[1][2]

In a streptoneurous animal, the right visceral nerve becomes a supraintestinal nerve (i.e., moving up from its former position along the intestines on the right side) and the left visceral nerve becomes a subintestinal nerve (i.e., moving down below the intestines and shifting to the right).

The extant gastropod molluscs can be described as streptoneurous. However, some lineages, especially the [opisthobranchs](/source/Opisthobranch),[2] have reversed this twist secondarily. The term for this event is *detorsion*, and the condition in a detorted animal— a state in which these nerves no longer cross— is called [euthyneury](/source/Euthyneury).[3]

## References

1. Hertwig, Richard & Kingsley, John Sterling (1905). [*A manual of zoology*](https://books.google.com/books?id=sQUFAQAAIAAJ&q=streptoneury&pg=PA373). H. Holt and company. p. 373.

1. Chase, Ronald (2002). [*Behavior and Its Neural Control in Gastropod Molluscs*](https://books.google.com/books?id=yowIPj0CeSEC&q=pericardium%20mammals%20molluscs&pg=PA6). Oxford University. p. 6. ISBN 9780195354485.

1. Barker, G. M. (2001). [*The biology of terrestrial molluscs*](https://books.google.com/books?id=WlvX-9Wt0toC&pg=PA185). CABI. p. 185. ISBN 9780851997186.

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