Blanket octopus
| Blanket Octopuses | |
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| Family: | Tremoctopodidae Tryon, 1879
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| Genus: | Tremoctopus Chiaie, 1830
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Tremoctopus gelatus | |
The blanket octopuses, four species of octopus in the Tremoctopus genus, are found in the waters of Australia's Northern Coast.
The male blanket octopus spends his existence drifting along waiting to meet with a female. If the male meets a female, he fills one of his tentacles with sperm and tears it from his body. He gives this sperm-filled tentacle to the female which she then uses to fertilize her eggs. Afterwards, the female leaves the male, who floats away and dies.
These species have an extreme degree of sexual dimorphism. According to the Melbourne Museum, "there's no other non-microscopic critter that has such a significant size difference between the male and female." Measuring only 2.4 cm long, the male blanket octopus is incongruously smaller than the female who can grow to over 2 m. This means that the female can be 100 times larger than her mate, and up to 40,000 times heavier. The male can afford to be small, since his chance of mating with a female and passing on genes does not depend on size, though the female's size is necessary to pass on as many healthy offspring as possible. The male's small size in fact allows him to reach sexual maturity faster, raising the chances that when a female stumbles upon him, he is ready to copulate.
The species has evolved an unusual defense mechanism: blanket octopuses are immune to the poisonous Portuguese man o' war, whose tentacles the male and immature females rip off and use for defensive purposes. Also, unlike many other octopuses, the blanket octopus does not use ink to intimidate potential predators, but instead unfurls a large net-like membrane which then spreads out and billows in the water like a cape. This greatly increases the octopus's apparent size, and is what gives the animal its name.
Species
- Gelatinous Blanket Octopus, Tremoctopus gelatus
- Tremoctopus robsoni
- Palmate Octopus, Tremoctopus gracilis
- Common Blanket Octopus or Violet Blanket Octopus, Tremoctopus violaceus
References
- Pickrell, John (Aug. 12, 2003). "Walnut-Size" Male Octopus Seen Alive for First Time. National Geographic News.
- Norman, M.D.; Paul, D.; Finn, J.; and Tregenza, T. (2002). First encounter with a live male blanket octopus: the world's most sexually size-dimorphic large animal. New Zealand Journal of Marine and Freshwater Research 36, 733-736.
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