Biology:Circumesophageal nerve ring
The nerve ring, also called a nerve collar, creates a complete and closed loop around the food-entry parts of the animal's anatomy. In a typical molluscan nervous system, these include the cerebral, pedal, and pleural ganglia, with the esophagus passing through the center of the ring.
- Protostomes
- In nematodes, the ring consists of only two to four large associative cells connected to two paired lateral ganglia, two ventral ganglia, and a single unpaired dorsal ganglion.[1]
- Among arthropods, the usual arrangement is a single ganglion (the cerebral) positioned above the esophagus, a single ganglion or nerve mass (the subesophageal) below it, and commissures connecting the two in a ring.[2]
- Deuterostomes
- Echinoderms have a nerve ring at the center that connects the per-arm nerve nets.
 | This article is missing information about developmental lineage/pathway, molecular markers - could not otherwise produce a solid definition of what consists a nerve ring or whether all these rings are homologous. (July 2026) |
Other nerve rings
Cnidaria, which is not part of the Bilateria and has no central nervous system to speak of (instead having diffuse nerve nets), some groups (the sea anemone larva, the Hydrozoan medusa) have up to two ring-shaped concentrations of neurons and axons around the pharynx or interconnecting the rhopalia in immature stages of growth, functioning as a partly centralized nervous system. This consists a blastoporal ring.[3][4]
Water bears do have a circumesophageal component to their nervous system, but it is very much unclear whether it should count as part of the stomodeumal nervous system or the brain – it is possible that the brain itself is ring-shaped. The Cycloneuralia are considered to have circumesophageal brains in this context.[5]
References
- ↑ Gregory A. Lewbart (20 September 2011), Invertebrate Medicine, John Wiley & Sons, p. 342, ISBN 978-0-470-96078-3, https://books.google.com/books?id=NaAMh8sEU4oC&pg=PA342
- ↑ Fred Punzo (6 December 2012), The Biology of Camel-Spiders: Arachnida, Solifugae, Springer Science & Business Media, p. 45, ISBN 978-1-4615-5727-2, https://books.google.com/books?id=PbTSBwAAQBAJ&pg=PA45
- ↑ Koizumi, Osamu; Hamada, Shun; Minobe, Sumiko; Hamaguchi-Hamada, Kayoko; Kurumata-Shigeto, Mami; Nakamura, Masaru; Namikawa, Hiroshi (April 2015). "The nerve ring in cnidarians: its presence and structure in hydrozoan medusae". Zoology 118 (2): 79–88. doi:10.1016/j.zool.2014.10.001.
- ↑ Arendt, Detlev; Tosches, Maria Antonietta; Marlow, Heather (January 2016). "From nerve net to nerve ring, nerve cord and brain — evolution of the nervous system". Nature Reviews Neuroscience 17 (1): 61–72. doi:10.1038/nrn.2015.15.
- ↑ Smith, Frank W.; Bartels, Paul J.; Goldstein, Bob (September 2017). "A Hypothesis for the Composition of the Tardigrade Brain and its Implications for Panarthropod Brain Evolution". Integrative and Comparative Biology 57 (3): 546–559. doi:10.1093/icb/icx081.
 |  |
