The Origin and Early Evolution of Metazoa

A generally conical cutting head for an underwater dredger includes a plurality of helical cutting arms 1 having teeth 4 mounted thereon. The arms are fixed at one end to a hub 2 and at the other end to a base ring 3. The tooth spacing between the respective cutting arms is arranged in a multi-staggered configuration whereby each tooth removes a symmetrical piece of soil and is not subjected to loads parallel to the local section of the contour line 5'.