The following is an answer to our question about the identity of this Cephalopod on the Cephalopod Research and Discovery discussion list on TONMO.com:
Dr. Steve O'Shea (Steve) -- Cephalopod Science Forum Moderator
Steve is an expert in the systematics and biogeography of cephalopods, and joined the TONMO.com staff in June 2002. He can be seen on the Discovery Channel documentary, Chasing Giants: On the Trail of the Giant Squid. For more information, see his Autobiography and Select Bibliography (2003). Dr. O'Shea lives in New Zealand. Email: email@example.com
It certainly is a species of Tremoctopus, a female (the male being considerably smaller), but which one I would be reluctant to say, based on the images alone.
Thomas (1977) reviewed species of the genus Tremoctopus and recognised two valid subspecies of T. violaceus, T. violaceus violaceus and T. violaceus gracilis, and a second species, T. gelatus. I (O'Shea 1999) resurrected another species, T. robsonianus Kirk, 1883, from synomymy of T. v. violaceus, so that three species were recognised, T. violaceus with the aforementioned two subspecies, T. gracilis and T. robsonianus. Males of T. v. violaceus and T. v. gracilis can be distinguished by the number of distal transverse sucker pairs on the hectocotylised arm: the former with 15-19, the latter, 19-23; the male ofT. gelatus was unknown (in 1999, when I researched the group; I don't know whether it has been described yet, but I doubt it); T. robsonianus has 27 or 28 distal transverse sucker pairs on the hectocotylised arm.
Female Tremoctopus species have proved difficult to distinguish. The distal oviducts of T. robsonianus are exceedingly long and convoluted, differing markedly from those of T. violaceus violaceus, T. v. gracilis andT. gelatus (in each the distal oviducts are depicted as short, each having a pronounced distal dilation).
You mentioned something about the animal carrying eggs. This is of great interest. I don't suppose you have any pictures of this do you? Female T. robsonianus do brood the eggs in the distal oviducts (as eggs contain embryos, indicating fertilisation is internal, occuring within the ducts somewhere (or possibly even in the ovary sac)). If they brood eggs in the oviducts then it is also of great interest that they brood eggs in the arm crown (I assume this is what was happening, unless there was a discharge of eggs from the mantle cavity during trauma associated with collection).
I'll find out the geographic distribution of Tremoctopus species to assist with placing a name on this particular specimen, although precise identification (based on those characters/character states that we recognise differentiate the various taxa) would really require the body (anatomy) of the animal be examined. T. robsonianus is presently known from New Zealand waters only, but it could well have a considerably more extensive distribution than presently recognised (very likely into South Australian waters also).
O'Shea, S. 1999. The marine fauna of New Zealand: Octopoda (Mollusca: Cephalopoda). NIWA Biodiversity Memoir 112: 280pp.
Thomas, R.F. 1977. Systematics, distribution and biology of cephalopods of the genus Tremoctopus (Octopoda: Tremoctopodidae). Bulletin of Marine Science 27: 353-392.