Several aspects of the biology of Opisthoteuthis calypso were studied based on 38 individuals (23 males, 14 females and 1 indeterminate) retrieved from bottom trawls fished at 871 to 1420 m depth in the Sardinian Channel (central western Mediterranean). Data on full maturity of females are presented for the first time for this species. Information on the distribution, size, structure and fecundity for both sexes is provided, and the biological characteristics of the Sardinian samples are compared to those of other Mediterranean and Atlantic samples. Morphological variability and the peculiar structure of the shell and beak are reported and discussed. Molecular DNA sequences were obtained and compared with sequences available for the genus Opisthoteuthis.
