%sphaeridium%

‖n.; pl. Sphaeridia [ NL., fr. Gr. &unr_;&unr_;&unr_; a sphere. ] (Zool.) A peculiar sense organ found upon the exterior of most kinds of sea urchins, and consisting of an oval or sherical head surmounting a short pedicel. It is generally supposed to be an olfactory organ. [ 1913 Webster ]