Squids of the family Gonatidae are key components in oceanic communities. However, issues related to correct species identification, number of species, and their genetic relatedness remain. To address these issues, sequences from three mitochondrial (cytochrome c oxidase subunit I [CO1], 16S rRNA, and 12S rRNA) and two nuclear (18S and 28S) genes were analysed in the Gonatidae. Four of the five sequences (12S rRNA, 16S rRNA, 28S, and CO1) yielded rather similar patterns of genetic relationships among the species. Molecular evidence suggested intra-familial subdivision into two major groups of species having either five or seven longitudinal rows of teeth in the radula. The former group included all species of the genus Gonatus and two sister-species of Gonatopsis s. str. suggesting that all gonatid species with five rows of radular teeth represent a single taxonomic unit of a genus or subfamily level. Species with seven rows of radular teeth formed several ‘species’ clusters. Sequence analysis also addressed species identification issues in the Gonatidae. Two genetically divergent groups were found among squid which conformed to the description of Gonatus berryi. Molecular evidence suggested sister-species relationships between ‘large’ and ‘small’ forms of Boreoteuthis borealis with size-at-maturity as the only reported difference between these two cohorts. Sequence variation was observed within Gonatus pyros. Inclusion of gonatid sequences from the GenBank into the analysis suggested probable species misidentification in several cases. Combined use of several mitochondrial and nuclear sequences served as a valuable tool for species identification and provided a solid background for unravelling molecular genetic and taxonomic relationships in the Gonatidae.

Nine specimens belonging to four separate species and two genera from Davis Strait and Hudson Strait exceeded the known maximum recorded sizes for their associated species. New size records are given for Bathypolypus pugniger, B. bairdii, B. arcticus and Cirroteuthis muelleri. All individuals were found within the same basin (532 to 1453 m) within Davis Strait with the exception of B. arcticus which was found along the trench (284 to 388 m) that runs through the middle of Hudson Strait. Six large sized Gonatus fabricii were also found in the same region of Davis Strait, but did not exceed the maximum size of 385 mm, a female caught in the Norwegian Sea. Since these two regions are the only areas where such large individuals were found, we speculate that these areas are of particular interest as potential spawning sites and are oceanographically and biologically favourable for the maintenance of large individuals.