Hancock's organ is a lateral concealed sensory organ of gastropods,Hancock, A., (1852). Observations on the Olfactory Apparatus in the Bullidae. The Annals and Magazine of Natural History Vol.IX – Series 2 188-190. a chemo-sensory sense organ found in some sea snails. This organ is found in most of the shelled opisthobranchs.Schrödl M. & Neusser T. P. (2010). "Towards a phylogeny and evolution of Acochlidia (Mollusca: Gastropoda: Opisthobranchia)". Zoological Journal of the Linnean Society 158: 124-154. .
A great majority of the bubble shells and sea slugs of the orders Acteonoidea and Cephalaspidea have Hancock’s organs.
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