The correct option is C Phaeophycea
The Sargasso sea is a region in the gyre in the middle of the North Atlantic Ocean. It is the only sea on the Earth which has no coastline. The ocean water in the Sargasso sea is distinctive for its deep blue colour and exceptional clarity, with underwater visibility of up to 200 feet. The Sargasso sea is home to seaweed of the genus Sargassum (Phaeophyceae), which floats en masse on the surface there. The Sargassum is not a threat to shipping and historic incidents of sailing ships being trapped there are due to the often calm winds of the horse latitudes.