So how do you actually identify an octopus species?


Apr 19, 2010
Let's focus on the ones that are mostly in private aquaria (I posted a dichotomous key to octopodids in this forum, but that focuses on genera).

- Octopus mercatoris
- Octopus bimaculatus
- Octopus bimaculoides
- Octopus briareus
- Octopus joubini
- Octopus macropus complex
- Octopus vulgaris
- Abdopus aculeatus
- Abdopus abaculus

A lot of these are near-undiscernable to the untrained eye.

Bimacs have the two eye spots, and Octopus vulgaris is a bit dark around the eyes. Any other characteristics you can list that distinguish any species?


Certified Ceph Head For Life
Staff member
Sep 4, 2006
Gainesville, GA
Can you wait until October? :sagrin: This is my topic (non-invasive and from a hobbiests point of view) for TONMOCON IV:wink: Any additional suggestions/corrections to include in my presentation would be most welcomed!

Without trying to give my presentation (which I have only outlined at this point), some of things a hobbiest can look for to id or elminate are:

Mantle to arm ratio (helps with briareus and vulgaris)
Mantle length to girth ratio (vulgaris having a lower ratio than most)
Size and positioning of eyes (the more prominant, the more likely it is nocturnal)
Ocelli, eyespots (primarily hummelincki and bimac - both species but we don't see bimaculatus
...Monty remains an unknown, not being either of these but having eyespots elimintates the common dwarfs,
...eyespot color elimates small hummelincki)
Ocean of origination (helps narrow down the species and determine water temp but often not available)
Web depth (particularly helpful with briareus as it runs the length of the arm)
Arm length and girth differences (often a set of arms is thicker and longer than the other 4 or 6,
...macropus that we see from Live Aquaria has very thin, shorter arms for L/R3 and L/R4,
...2nd arm on briareus is noticeably thicker)
Protrusions on the skin (or lack of, joubini shows almost none, mercatoris only a few,
...bimac dislays a few thick spikes, briareus displays small bumps,
...aculeatus can look like seaweed with many fine protrusions)
Consistent (mostly) patterns (star around the eye for aculeatus, striping on the arms for several, pattern on the head,
...speckled peach underside often shown on hummelincki)
Color displays (the number of colors displayed outside of white and brown,
...hummelincki shows orange/yellow spots and blue lines, bimac shows yellow spots all over when mottled,
...briareus shows a peach mottling, golden yellowish all over is aculeatus typical, orangeish red - vs brown red -
...typical of joubini and most in macropus complex)
Color of rim around suckers (aculeatus and hummelincki have purple/blue, bimac has orange, briareus white)
Size of eggs (primary way to tell bimaculoides from bimaculatus other than size at death but there is a
...difference in their ocelli )
Reflective green spots (briareus and at least one in the macropus complex,
...shows up well with photographs or night dives with flash light)
Number of rows of suckers (all the common ones we see have two side by side rows.
...Some have a single row and some have a double row that is off-set)

Things I can think of that might seem diagnostic but are not because all of these species can display the trait:

Coloring all white or all dark brown
Passing cloud color changes
Parallel white spots about half way back on the mantle (have not been able to find out what these are but
...they seem to be in the position of the ink sacs.
Thin or thick ink
Dark coloration around the eyes (owl look - defensive to look larger, may show a guarded vs relaxed state even when interacting)
Skin protrusions under the eye - I have seen most show these at one time or another once I started looking for them,
...some species (aculeatus) show them most of the time though.

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