Abstract
A morphometric analysis using certain taxonomic characters of adult males of Calanus finmarchicus (Gunnerus) and C. glacialis Jaschnov shows that the taxa comprise two non-overlapping clusters. Calanus finmarchicus and C. glacialis are probably reproductively isolated. Differences between the species in geographical distribution, vertical distribution, and timing of life cycles also support this conclusion. Previous taxonomic studies of adult females of the two species have yielded inconclusive results, probably because the analyses were based largely on subgeneric characters.