Nuchal organ explained

The nuchal organ is a ciliated pit^[1] or groove present at the posterior end of the prostomium of annelid worms,^[1] some cephalopods, and other invertebrates.^[2]

Annelids only possess one nuchal organ, although the nature of the grooving may make it appear to be a pair of organs.^[3]

It may be involved in light detection,^[4] and may have a role in food detection and mating.^[5]

Notes and References

1. Hessling. R.. Purschke. Günter. Immunohistochemical (cLSM) and ultrastructural analysis of the central nervous system and sense organs in Aeolosoma hemprichi (Annelida, Aeolosomatidae). Zoomorphology. 23 October 2000. 120. 2. 65–78. 10.1007/s004350000022. 38957268.
2. Peñalva-Arana. Carolina D.. Manca. Marina. An SEM study of the nuchal organ in Daphnia himalaya (nov. sp.) embryos and neonates collected from the Khumbu region (Nepalese Himalayas). Journal of Limnology. 1 August 2007. 66. 2. 153. 10.4081/jlimnol.2007.153. free.
3. Purschke. G.. Wolfrath. F.. Westheide. W.. Ultrastructure of the nuchal organ and cerebral organ in Onchnesoma squamatum (Sipuncula, Phascolionidae). Zoomorphology. 21 March 1997. 117. 1. 23–31. 10.1007/s004350050026. 39830837.
4. Parry. Matthew. A description of the nuchal organ, a possible photoreceptor, in Euprymna scolopes and other cephalopods. Journal of Zoology. October 2000. 252. 2. 163–177. 10.1111/j.1469-7998.2000.tb00612.x.
5. Schlötzer-Schrehardt. U.. Ultrastructural investigation of the nuchal organs of Pygospio elegans (Polychaeta). I. Larval nuchal organs. Helgoländer Meeresuntersuchungen. December 1986. 40. 4. 397–417. 10.1007/BF01983820. free. 1986HM.....40..397S .