Sea anchor
Modern commercial sea anchors are usually made of cloth, shaped like a parachute or cone, and rigged so that the wider end leads and the narrower end trails. When deployed, this type of sea anchor floats just under the surface, and the water moving past the sea anchor keeps it filled. Some varieties are cylindrical, with an adjustable opening in the rear that allows the amount of braking to be adjusted when deployed.
Vacuum-anchor
In large scale oceanic civil engineering, vacuum-anchors are ocean bottom fasteners used to anchor deep seas oil platforms (example: See Troll A Oil Platform) and other gravity base technology based structures in the soupy soft bottomed muck found on many oil bearing continental shelves and the world's shallower seas. Gravity based anchor legs flare out forming a wider footprint where they contact the bottom much as the webbed feet of many aquatic animals increase the surface area above the vacuum-anchors which are open ended long cylindrical shaped deep cups with a sealed top end closed by a valve which connects and anchors mechanically to the legs of the gravity based structure. The valve is used to exhaust any gases and liquid which seeks to escape the trapped sea bottom materials entering the open end of the anchor.