Euphasiids - or krill - are eucarid crustaceans represented by 2 families, the Bentheuphausiidae and the Euphausiidae. They are the most economically important component of the oceanic plankton biomass in terms of size and abundance, and form a significant food item for whales, seals, fish, birds and now man. This key is aimed at workers unfamiliar with their taxonomy, and is also a general introduction to the order.