A living scarf: The blanket octopus

I post on cephalopods as rarely as I do on dogs, but at least I don’t have an “anti-cephalopod Tuesday.” But some of them are so weird that I can’t resist. A recent post by Katherine Harmon at Octopus Chronicles of Scientific American describes a small group of octopi that go under the name “blanket octopus” (four species in the genus Tremoctopus).  Besides their strange vampire-ish appearance, with the tentacles enclosed in a “cape,” they have an unusual defensive behavior (co-opting the tentacles of a jellyfish) and, especially, the most extreme sexual dimorphism and bizarre mating behavior I’ve heard of in any mollusc. From Wikipedia:

These species exhibit an extreme degree of sexual dimorphism. Females may reach 2 m in length, whereas the tiny males are at most a few centimeters long. The males have a specially modified third right arm which stores sperm, known as a hectocotylus. During mating, this arm detaches itself and crawls into the mantle of the female to fertilize her eggs. The male dies shortly after mating. The females carry over 100,000 tiny eggs attached to a sausage-shaped calcareous secretion held at the base of the dorsal arms and carried by the female until hatching.

As National Geographic describes, the walnut-sized males, weighing only 1/40,000th as much as the females, weren’t even seen alive in the wild until 2003:

Blanket octopuses are rarely seen. They spend their entire life drifting in the open oceans of warm regions worldwide. Females have the odd appearance of a “big pink drifting blanket” said Tregenza, explaining the origins of the octopus’s name.

Among their more unusual behavior, the octopuses employ a unique defense mechanism by tearing off the tentacles of passing Portuguese man-of-war jellyfish. The octopuses are immune to the tentacle’s painful sting. When they encounter potential predators, the octopuses waft the captured man-of-war tentacles in two pairs of its upper arms as an effective deterrent.

The male blanket octopus recently photographed by researchers was shown to clutch tentacle segments in his suckers, said Tregenza [Tom Treganza from the University of Leeds].

. . . If a male does chance across a female, it uses all its resources in an attempt to mate, “as he’s unlikely to encounter another one,” said Tregenza. A male blanket octopus fills a modified tentacle with sperm, tears it off, presents it to its prospective mates, and then drifts off to certain death.

Females store the tentacles inside large internal body cavities until they are ready to lay their eggs. At that time, the female pulls the tentacle out and “squeez[es it] like a tube of toothpaste,” over the eggs, said Tregenza.

This video showing the females was embedded in Harmon’s piece; there’s a really nice shot at the end of a school of fish in an antipredator formation:

And here’s another video taken in the Gulf of Mexico (warning: annoying music!):

It’s not so easy to find pictures of those diminutive males, but here’s one:

Image: Dhugal Lindsay/JAMSTEC/CMarZ

Image: Dhugal Lindsay/JAMSTEC/CMarZ

The mating behavior remind me of the anglerfish, deep-sea creatures in which the males are also very tiny, but also parasitic.  When a male finds a female, he attaches himself permanently to her body, absorbs his head, and fuses his tissue and bloodstream with that of the female.  He becomes, in effect, just a lump on the female’s body, ready to fertilize her eggs. (See a nice video of that here.) This behavior is obviously adaptive for a deep-sea creature, for females are so rare that when you find one, it’s best to never let her go (h/t: to South Pacific).

I often describe anglerfish to my undergraduate students, noting that the male is “nothing more than a parasitic sack of gonads—much like a male undergraduate.” The women students love that.


  1. Marella
    Posted April 9, 2013 at 5:35 am | Permalink

    I’d love to know what that octopus does with all that ‘curtain’. Very weird.

  2. infiniteimprobabilit
    Posted April 9, 2013 at 5:57 am | Permalink

    Y’know, if I was a Creationist, I’d be forced to conclude that God was not only sadistic, but deeply, ingeniously perverted as well. 😉

    • moarscienceplz
      Posted April 9, 2013 at 2:37 pm | Permalink

      Good thing that none of ’em ever actually read the Bible, else they might come to that conclusion as well!

  3. James C. Trager
    Posted April 9, 2013 at 6:18 am | Permalink

    Please cease and desist from the use of “octopi” as the plural of octopus. In English, the plural is quite correctly rendered as octopuses. Some people make it like fish or deer and thus don’t have a differentiated plural form. If you want to go all Hellenic, you can say “octopodes”. But, please not “octopi”!
    Explanation: The word is formed from two Greek roots, octo (eight) + pous – shortened to pus (foot). The latter evolved from Proto-Greek /pods/, and also occurs in in tripod, cephalopod, arthropod, etc. The plural of Greek pous is podes.
    But, there is nothing wrong with using a standard English sort of plural for a word that has been completely adopted in the English language, so I argue for octopuses.

    • Gregory Kusnick
      Posted April 9, 2013 at 11:00 am | Permalink

      While your etymology is sound, the reality is that “octopi” is in widespread use as an acceptable plural of “octopus”, and recognized by many dictionaries as such.

      What this says to me is that the “-i” rule for forming plurals has been naturalized into the English language and may be legitimately applied to any English noun ending in “-us” regardless of etymological origin.

      • moarscienceplz
        Posted April 9, 2013 at 2:30 pm | Permalink

        “One rhinoceri
        cannot get on a bus.
        For one rhinoceri
        is two rhinoceros.”

        Alan Sherman

        • infiniteimprobabilit
          Posted April 10, 2013 at 2:34 am | Permalink

          So, the rhinoceri would in fact need a pair of bi?

          (I’ve been longing to use that pseudo-plural for ages : )

    • Mark Joseph
      Posted April 12, 2013 at 7:14 pm | Permalink

      Support for the thesis of Mr. Trager is found in the very interesting “Ask the Editor” video at http://www.youtube.com/watch?v=wFyY2mK8pxk

      • Gregory Kusnick
        Posted April 13, 2013 at 12:06 am | Permalink

        OK, I’ve watched that video, and I don’t see how it supports Mr. Trager’s thesis that “octopi” is wrong and should not be used. On the contrary, it says that both “octopuses” and “octopi” are acceptable and that partisans of one do not get to say that the other is wrong.

  4. Victoria Ruddick
    Posted April 9, 2013 at 6:21 am | Permalink

    Fascinating. Did anyone notice when, in the second video, she detached part of her body? Another defense mechanism?

    • Torbjörn Larsson, OM
      Posted April 9, 2013 at 7:29 am | Permalink

      I suspect it is the usual ink. Isn’t it behaving like that in some species in order to mimic a decoy body?

  5. DavidIsaac
    Posted April 9, 2013 at 7:27 am | Permalink

    Hmmm … the male blanket octopus closely resembles the late-stage of the squid embryos I studied one summer at Wood’s Hole (following the MBL Summer Embryology course). Could this be another case of neoteny/paedogenesis?

  6. bacopa
    Posted April 9, 2013 at 11:23 am | Permalink

    I’m going out into deep water next month. The blanket octopus is native to my area, I’ll be sure to ask the skipper if she’s seen one.

    I’ve seen plenty of other octopuses on my trips. When you’re fishing for onaga near the little coral reefs that form on the deepwater rigs an octopus. The ocs perceive the hooked fish as a dying fish and try to get their noms from it. They let go of the fish in the landing net and we release them back into the water. If you don’t see any ocs, then you will soon see sharks. Sharks love the deep water sport boats.

  7. Divalent
    Posted April 9, 2013 at 12:44 pm | Permalink

    Now come on! That angler fish link is boring! Why not link to the best? http://www.youtube.com/watch?v=Z-BbpaNXbxg

    • Posted April 9, 2013 at 2:52 pm | Permalink

      We saw that one before, here, but it’s still awesomely funny.

  8. Mary Canada
    Posted April 9, 2013 at 1:56 pm | Permalink

    Very beautiful octopuses. Also liked the reference to male Undergraduates!

  9. Posted April 9, 2013 at 2:47 pm | Permalink

    Great videos. WRT “A male blanket octopus fills a modified tentacle with sperm, tears it off, presents it to its prospective mates, and then drifts off to certain death. “,
    do they always die from doing this?

    • DavidIsaac
      Posted April 11, 2013 at 7:21 am | Permalink

      Yes, and male squid (e.g., Loligo pealii) only live a single mating season and die soon after mating, even though they are comparable in size to the females of the species. I wonder about giant squid, though.

  10. dmcw
    Posted April 10, 2013 at 2:49 am | Permalink

    Some UK readers might agree that “parasitic sack of gonads” would also be quite a good description of Mick Philpott

  11. Posted August 14, 2013 at 3:55 am | Permalink

    what are those fish doing at the end of the video?? I mean: there’s somethink about the “blanket octopus”????

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