Which form of algae is most commonly used to wrap raw fish and rice in sushi?

Nori. The black seaweed wrappers used in makimono are called nori (海苔). Nori is a type of algae, traditionally cultivated in the harbors of Japan. Originally, algae was scraped from dock pilings, rolled out into thin, edible sheets, and dried in the sun, in a process similar to making rice paper.