The aim of the present study was to provide the first analysis of depth distribution and reproductive biology in the deep-sea cirrate octopus Opisthoteuthis calypso along the Portuguese continental slope. We used 77 specimens obtained in 7 research cruises between 1996 and 2003. Catch rates and biomass, weights, lengths, sex and maturity stages, and a morphometric description of the beak are detailed. Specimens have been collected from 553 to 960 m depth, south of 39°N, in approximately 1:1 sex-ratio. Females are larger (80:75 mm mantle length) and heavier (622:346 g total body weight) than males and both sexes have been caught in all stages of maturity in equal proportions.
