Octopus with branching arms

We see bifurcating arms once or twice a year and always in the larger (= older) animals (Octopus vulgaris). As we always see them on the tips of the arms (rather than being a whole extra arm (e.g. 9)) and we know the arms regrow after injury, I've always thought it represents what sometimes happens after regrowth rather than a mutation.. But I could be wrong. We also see the same thing sometimes in regenerating starfish arms. To my knowledge no one has made a special study of this.
 
Here's a paper:
Toll, R.B.; Binger, L.C. 1991. Arm anomalies: cases of supernumerary development and bilateral agensis of arm pairs in Octopoda (Mollusca, Cephalopoda). Zoomorphology 110: 313-316.

The abstract goes as follows:
The first case of true hexapody among the Octopoda, resulting from bilateral agensis of one arm pair, is described for a male Pteroctopus tetracirrhus. A case of decapody, with uniform development of all arms, is also reported for the first time for a male Octopus briareus. Both conditions apparently result from developmental anomalies of the embryonic arm anlagen. A survey of other anomalous conditions relating to arm devlopment and regeneration within the Cephalopoda is provided. A possible relationship of polyfurcation of arm tips in the Octopoda with regenerative processes in amphibian limbs leading to similar conditions is suggested.

They cite the following papers:
Gleadall, I.G. 1989. An octopus with only seven arms: anatomical details. Journal of Molluscan Studies 55: 479-487.

Kumph, H.E. 1960. Arm abnormality in Octopus. Nature 185: 334-335.

Okada, Y.K. 1935. An octopus with branched arms and mode of branching. Annot. Zool. Japon. 15: 5-23.

Okada, Y.K. 1937. An occurence of branched arms in the decapod cephalopod, Sepia esculenta Hoyle. Annot. Zool. Japon. 17(1): 93-94.

Okada, Y.K. 1965a. On Japanese octopuses with branched arms, with special reference to their captures from 1884 to 1964. Proc. Jap. Acad. 41(7): 618-623.

Okada, Y.K. 1965b. Rule of arm-branching in Japanese octopuses with branched arms. Proc. Jap. Acad. 41(7): 624-629.

Palacio, F. 1973. On the double hectocotylisation of octopods. Nautilus 87(4): 99-102.

Robson, G.C. 1929. On a case of bilateral hectocotylisation in Octopus rugosus. Proceedings of the Zoological Society of London, 1929: 95-97.

Smith, E.A. 1907. Notes on an "Octopus" with branching arms. Ann. Mag. Natur. Hist. 7: 407-411.
..........
Sorry about the abbreviated reference citation for many; this is as is in Toll & Binger's paper; I can cite full details shortly (just need to check those Japanese ones out).

Cheers
O
 
Is it possible that the freak shown in the photo above was producing at least some of those furcations in response to non-arm-severing injuries?
 
Here's the Smith article; it's quite brief but does include a (rather whimsical) illustration, partially reconstructed since he mentions most of the head and viscera having been removed. :roll:

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It's only been 14 years since someone commented on this thread... time to resurrect :periscop:

I've seen something similar in squid twice, as well. One was a submature specimen of Onykia robusta where it looked like some arm damage had resulted in regenerating suckers, but also a bit of haywire arm regeneration, almost like an additional arm with a dense cluster of suckers was branching off (see attached black & white fig). On MBARI's Western Flyer a couple years ago, we also got a specimen of Octopoteuthis deletron where one of the arm-tip photophores (which are known to autotomise) was bifurcated (attached color fig).
 

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It's only been 14 years since someone commented on this thread... time to resurrect :periscop:
Love it!

One was a submature specimen of Onykia robusta where it looked like some arm damage had resulted in regenerating suckers, but also a bit of haywire arm regeneration
Interesting... so yeah maybe if there's a wound or something mid-arm, the arm regeneration just kicks in at that spot...
 

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