[Hydromedusae] Median projection of the subumbrella surrounding the gastric cavity, distally bearing the terminal mouth and proximally leading to the radial canals. The manubrium is very variable in shape and size: tubular, cruciform, quadrate, fusifom, barrel-shaped, flask -shaped, short, long, narrow or very large, etc.
[Cubo-/Scyphomedusae] A central, tubular, downward projection of the subumbrellar surface bearing the mouth terminally, its lumen being continuous with the gastrovascular cavity (stomach). Greatly varied in shape and length between species.
[Siphonophora] Central structure inside gonophore on which the sexual products are developed.
Side view P. rubiginosa