Bimaculoides or Bimaculatus


Larval Mass
My brother and I came across 10 or 11 adult Bimac Octopi on a dive recently. They were at about 60ft depth, sandy bottom, and about between 12 to 18 inches from arm tip to arm tip. We were filming, and I want to accurately title the video, so I need to determine if they are Bimaculatus or Bimaculoides. The best view of the eye spot rings is at around 2:34 in the video. I titled the video Bimaculatus because that was my first guess; should I change the title to Bimaculoides? What say you?


Larval Mass
Bimaculoides vs Bimaulatus.
I reaize this is an old thread, but I am trying to settle this question with regard to several individuals I recently filmed. They appear to have had a distinctly chain-like and unbroken blue ring. However they were fairly large in size (12'-18' arm span) and in 60 ft of water. Here is the video, best look at the ring occurs at 2:34

I don't want my video title to be incorrect so hopefully someone will see this resurrected thread and weigh in. Thanks

Edit: consolidated to ID thread for best response. "D" - video link in initial post.


Staff member
Sadly, this is not a challenge I can even make a good guess to and I fear this will be true for all of our members. The size is within limits for both and I have read that the visual differences can only fully be detected in a necropsy (or possibly with a magnifying glass on the chain - I have doubts on this one though but I have never seen a confirmed O. bimaculatus). One for sure way IF it was female and IF you can return and find eggs (unlikely, I know) is egg size. The one clear difference for hobbyists is Bimaculoides is a large egg species and bimaculatus lays small eggs that are planktonic at hatching.

The best suggestion I can give for the video is to entitle it with both names or use the joint common name (Bimac) and explain the two possible species in your notes.


Staff member
:welcome: to TONMO - great video!

I am moving your posts to the ID thread for best response.

Please do not double post requests. Our staff is small but very responsive. Double posting only splits the thread and hinders the best efforts of all members.

That being said, I would encourage you to post the video on our Diving and Ceph Encounters forum and reference a link to the ID request (or reference the video post in the this request - I can change the links if you want to do it this way).

Also, does Vimeo give another option for bulletin boards that will allow embedding? I know you have opened the video for HTML/FLASH embedding but VBulletin (and others) needs a link format and does not provide for the standard HTML object. I believe this would be something you would have to enable as it is not part of the current sharing offerings.


Haliphron Atlanticus
I've seen a lot of bimaculoides, but I've never examined a bimaculatus up close (they tend to live deeper). That said, based on the published differences, I think it's very likely that you filmed a bimaculoides, not bimaculatus. The bimaculatus is supposed to have a blue ring "with radiating spokes". If I ever get a good picture of the spot on a bimaculatus I'll post it here for comparison.

Besides the difference in egg size, and the "spokes", I found one source that said that bimaculoides ink is black, while bimaculatus ink is brown.

for reference, here are the sources:

The Light and Smith Manual
Intertidal Invertebratesfrom Central California to Oregon
4th edition - Page 700

Octopus Bimaculoides Pickford and McConnaughey, 1949....two dark ocelli present, each with necllace-like iridescent blue ring...

Octopus Bimaculatus Verrill, 1883. ...two dark ocelli present, each with iridescent blue ring with radiating spokes...

Compiled by Dr. Roland C. Anderson, The Seattle Aquarium

7. Iridescent blue ring of ocellus chain-like, eggs large, benthonic larvae, most commonly lives on mudflats, black ink............................Octopus bimaculoides
Iridescent blue ring of ocellus with radiating spokes, eggs small, planktonic larvae, generally lives on rocks, brown ink......................................Octopus bimaculatus​


Larval Mass
Thank you Joe. I blew up some of the footage and examined the ring closely and it is indeed an unbroken chain link pattern, meaning this is a bimaculoides. Thanks for the help.

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