sphaeridium

== English == === Etymology === From Ancient Greek σφαιρίδιον (sphairídion, “sphere (diminutive form)”), by surface analysis, sphero- +‎ -idium. === Noun === sphaeridium (plural sphaeridia) (botany) Synonym of capitulum. (zoology) A sense organ found on the exterior of most sea urchins, consisting of an oval or spherical head surmounting a short pedicel. It is generally supposed to be an olfactory organ, or for equilibrium.