Population structure
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Research study 1
  How related are the west-coast octopus species?  This is investigated for the 4 common shallow-water species Enteroctopus dolfleini, Octopus rubescens, O. bimaculoides, and O. bimaculatus, with the addition of a deep-water Californian species Octopus californicus, by researchers at Simon Fraser University, British Columbia.  DNA-sequencing results suggest that O. bimaculoides and O. bimaculatus form their own clade, separate from a clade containing Enteroctopus dolfleini and O. californicus.  Octopus rubescens is separate from the others, but possibly more closely aligned with the southern California group.  Sosa et al. 1995 Mol Phylogenetics & Evol 4 (2): 163. 
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Research study 2

map showing clades of octopuses Enteroctopus dolfleini present at 3 locations in western AlaskaA later study by researchers from Alaska Pacific University and the U.S. Geological Survey, Anchorage provide genetic sequencing data for giant octopuses Enteroctopus dolfleini in western Alaska that comprise 2 separate clades (I and II), strongly suggesting that there are actually 2 species present. Arm tips from octopuses at three main sites (Dutch Harbor, Kachemak Bay, and Prince William Sound) are sampled and analysed for various mitochondrial and nuclear genes, and for 18 microsatellite loci. Results suggest the presence of a cryptic Enteroctopus species (Clad II) that is related to, but separate from E. dolfleini (Clad I) in Prince William Sound, Alaska (see map). Until specific morphological and other analyses are done the exact placement of the new Clad II within genus Enteroctopus cannot be known. Toussaint et al. 2012 Conserv Genetics 13: 1483.

NOTE the authors explain their broader-than-normal gene selection on the fact that previous investigations on population structure of E. dolfleini have been primarily based on nucleotide sequences of the mitochondrial genes cytochrome c oxidase subunits I or III, and in their opinion neither of these may be sufficiently polymorphic to be confident of the data

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Research study 3

Another similar study by researchers at University of Alaska Fairbanks investigates the population structure of Enteroctopus dolfleini in Alaskan waters, with additional specimens being obtained from another site in Alaska, and from sites in British Columbia, Washington, and map showing populations of octopuses Enteroctopus dolfleini sampled for genetics studyOregon. Results disclose the presence of 2 distinct haplotypes, with a third one in southern Alaska less well represented (see map). The main lineage extends from northern Oregon to the Aleutian islands, while the second has more restricted distribution within the Gulf of Alaska. The authors note that the data presented here are consistent with an earlier suggestion that the 2 distinct mitochondrial lineages could represent cryptic species (see Research Study 2 above). The main haplotype described here closely resembles one described earlier for E. dolfleini in British Columbia, and at 2 sites in Japan. Barry et al. 2013 J Moll Stud 79: 133.

NOTE samples prepared from muscle tissue of arms are are sequenced from the cytochrome oxidase I locus of the mitochondrial genome

NOTE whereas sample numbers for the main collections at 5 sites in Alaska range from 18-45 (save for Kodiak Island, which is 2), sample numbers for these additional sites range only from 1-4. For this reason the authors exclude them from their main analyses, but remark that these new inclusions match the predominant haplotype found in the main Alaska sites