Characterized by spines on its long second thoracic appendage, Nematoscelis difficilis is a common euphausiid of the California Coastal Ecosystem, and endemic to the North Pacific Ocean and Gulf of California. The species has bilobed eyes that have approximately equal sized halves. Like other Nematoscelis species, N. difficilis are gonochoric and show sexual dimorphism between males and females. Unlike other Nematoscelis species, N. difficilis females have a membranous sac on their ventral side to hold her eggs; most Nematoscelis species are broadcast spawners.
