Description from Muctopus:
Amphioctopus marginatus (Taki, 1964) PDF from eolSpeciesLifedesks.org
There are two color morphs described (and possibly more out there). One has distinct bright white sides of the suckers, and the funnel might not be very yellow. A. marginatus can have a transient blotch on the side that looks ocellus-like, but it's not well defined (more like a uniform purplish thumbprint), and it isn't visible all the time. The purple margins are sometimes not prominent as well. A. marginatus has fairly bumpy-looking skin, the tops of the bumps are pale or light purple, and the grooves in between are purple- this is because the skin is stretched over the bumps and chromatophore density lower (and higher in the grooves). Sometimes there is a dark purple triangle on each side of the eye (if I have time I'll post pics in the next few days). The lines on the arms are dark purple- when they show them- and run only from the base of the arm to the tips, right along the top edge of the suckers. If you have access to an academic library, look at the pics in "Field observations of mating in Octopus tetricus Gould, 1852 and Amphioctopus marginatus (Taki, 1964)(Cephalopoda: Octopodidae)". If not then PM me and I'll send you the pdf. Perhaps most notable about A. marginatus and other members of the genus is the distinctly short front arms (Arms I) and the very shallow front web (web A- the webbing between the two front arms). This group also has much shorter, thicker arms (usually appearing about 1.5-3 times as long as the mantle length, depending on the position) relative to the larger mantle as compared to A. aculeatus.