rhopalium

rhopalium (noun; plural -lia; Greek rhopalon, club): (Cnidaria) A hollow tentacle or sense organ with endodermal statoliths and rarely ocelli, that lay in each notch between the lappets at the end of a pedalium; lithostyle; statorhabd; tentaculocyst; statocyst

See also: colletocystophore.