Any member of the crustacean suborder Euphausiacea, comprising shrimplike animals that live in the open sea. The name also refers to the genus Euphausia within the suborder and sometimes to a single species, E. superba. The described species, numbering more than 80, range in size from about 0.25 to 2 in. (8–60 mm). Most have bioluminescent organs on the lower side, making them visible at night. They are an important source of food for various fishes, birds, and whales, particularly blue and fin whales. Krill may occur in vast swarms at the ocean surface, where they feed at night, and at depths greater than about 6,000 ft (2,000 m). Because of their vast numbers and nutritive qualities (they are an especially rich source of vitamin A), krill have been regarded as a potential source of food for humans.