The Blanket Octopus (Tremoctopus violaceus) is a member of the cephalopod family, which includes species of octopi, cuttlefish and squid. However, unlike the common octopus discussed previously on this blog, the blanket octopus is pelagic; meaning it travels great distances and is adapted to life in the open sea. Unlike inshore waters, which contain reefs habitats, and unlike the deep ocean, where organism congregate on the silty bottom, the open sea appears a vast oceanic desert. Animals found in the pelagic zone include jellyfish, dolphins, whales, pelagic fishes such as tuna, and seafaring birds, like terns.
Most pelagic animals are characterized by a streamlined body capable of carrying them over lengthy migrations, and one that is usually dark on the top, promoting camouflage from the air, and light on the bottom, promoting camouflage from below. In addition, they usually have good eyesight, and feed on the abundant plankton and algae in the sun-rich upper-pelagic zones of the ocean.
The blanket octopus, however, ascribes to few of the aforementioned characteristics. Though many pelagic animals are dully coloured and designed in all ways to move forward, the blanket octopus is one of the most flamboyant inhabitants of the ocean. The female blanket octopus sports impressive webbing connecting her dorsal and dorsalateral arms, resulting in an animal capable of reaching about two meters in length. As far as scientists can tell, this webbing is used by female blanket octopi to scare away predators when threatened, in addition to the ink that most cephalopods are capable of producing.
These creatures exhibit dramatic sexual dimorphism; difference in size between males and females of the species. While the female can be up to two meters in length, the male is just a few centimeters long. Males possess a modified arm, known as a hectocotylus, which stores sperm for mating. This arm crawls in to the mantle of the female to fertilize her eggs, a process which results in the death of the male shortly thereafter.
The animals are quite rare, though there have been reports of blanket octopi being seen by Bermudians. For example, this account was found on reddit, supposedly from a taxi driver who had seen one:
“It was a big momma octopus, nothing to f**k with. It was huge, it sat out in the water staring at me, turning fifty colours I hadn’t ever seen before! Just kept flashing back and forth; blues and greens and reds and pinks no one has even thought of yet! Then it extended its big blanket and sprayed poison out of some pores or something, and that’s the last thing I remember. Woke up with people standin’ over me asking what was wrong, the poison made me black out! It was a crazy time and I tell everyone. Asked some scientists, they said it was some sort of rare one that most people don’t see in a lifetime. I wanted to believe I was hallucinating, but no. Big momma octopus was real, and I’m one of the only people to ever see it! Crazy experience, right?”
The colours the man refers to are likely a reference to the octopus’ iridescence, amplified by the undulation of its webbing.
In addition, the blanket octopus is immune to the sting of the Portuguese Man O War (Physalia physalis), a cnidarian common in Bermuda. The Man O War is also a pelagic animal, characterized by its blue balloon like pneumatophore and trailing, venomous tentacles than can reach 10-50 meters in length. Nematocysts in the Man O War’s tentacles deliver a fatal sting to any fish the organism comes across in the water, and a nasty sting to any human it comes in to contact with. Because of their immunity to the venom of the Man O War, blanket octopi are able to rip off tentacles of the cnidarian and use them for defensive purposes, as the venom can stay alive for extended periods of time in dead tentacles.