[Cnidaria] In some medusae, a cone-shaped thickening projecting downwards from the subumbrellar mesoglea into the subumbrellar cavity, bearing the manubrium; radial canals run down the peduncle to reach the manubrium; varied in shape and size (e.g., long and narrow in Eutima mira; large and pyramidal in Bougainvillia macloviana; very short in Phialopsis diegensis).