I was surprised by both the article (stunning pics) and the name 'blanket octopus' (I'm not really up on the common names .... another has been referred to as the 'football' octopus I believe).
The animal in question is a species of Tremoctopus, out there in its own family, the Tremoctopodidae (with 3 species and 1 subspecies presently known: Tremoctopus violaceus violaceus, T. violaceus gracilis, T. gelatus, and T. robsonianus). There are two closely related octopus families: the paper nautilus (Argonauta spp., family Argonautidae) and another weird thing, Ocythoe tuberculata (family Ocythoidae); species in all three families are pelagic, and the male of each is disproportionately small (I think you'll find the degree of sexual dimorphism to be greater/more pronounced in Ocythoe tuberculata; I'm not sure if the fully mature [and quite masive] female Ocythoe has been photographed live - should this be the case it would be another quite another stunning first). There are pics of both Argonauta (an immature female) and Ocythoe (fully mature male) in the photo gallery. We have a pic of a male Tremoctopus due out in a book here soon .... but that's not important....the pic Mark et al. present in this paper is a stunner.