In addition, many marine creatures find shelter in seaweed beds. There are about 7,000 species of seaweeds. Algae lack true roots, stems, leaves, and flowers. However, their special structure suits seaweeds to a life of pounding by the sea. Some types of seaweeds Marine algae can be found from the polar seas to the tropics.
Most varieties grow near coasts, where they are attached to rocks, shells, or the floor of the sea.
A rootlike part, called a holdfast, anchors larger seaweeds to solid objects and prevents them from being washed away. Unlike a true root, the holdfast is not specialized to absorb water and minerals. A frond, which resembles a stem and leaf, extends from the holdfast. The soft, flexible fronds of a seaweed can sway with the water without being torn apart. Some seaweeds have gas-filled swellings on their fronds.