Nuchal organ

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

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

[4] It may be involved in light detection,[2] and may have a role in food detection and mating.

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