“Blanket octopus” sounds like an endearing nursery game, but the blanket octopuses are actually pelagic hunters which have adapted to living in the ultra-competitive environment of the open ocean. There are four species of blanket octopuses (Tremoctopus) which can be found ranging from the surface to medium depths of open tropical and subtropical seas worldwide. Because they often live far from any land, some of the methods which other octopuses use to escape predators do not work very well for them. Fortunately Blanket octopuses have adapted in their own unique bag of tricks.
Blanket octopuses are named after the distinctive appearance of adult female octopuses which grow long transparent/translucent webs between their dorsal and dorsolateral arms. Blanket octopuses use these webs as nets for hunting fish, but they can also unfurl and darken their nets in order to appear much larger than they actually are. Since blanket octopuses do not produce ink and can not camouflage themselves as rocks, coral, or sand, they rely heavily on their blankets. As a last resort they can jettison the blankets as a decoy and jet away while the confused predator attacks the highly visible membranes.
Blanket octopuses exhibit extreme sexual dimorphism. Whereas the female octopus can grow up to 2 meters (6 feet) in length, the male octopus is puny and does not grown longer than a few centimeters (1 to 2 inches). Males store their sperm in a modified quasi-sentient third right arm, known as a hectocotylus. During mating this arm detaches itself and crawls into the female’s reproductive vent. As soon as the hectocotylus is detached the male becomes unnecessary and dies.
Tiny males and immature females do not have blankets, but they utilize another trick to protect themselves. Because they hunt jellyfish and other hydrozoans, the little octopuses are immune to the potent venom of the Portuguese man o’war. The octopuses tear off stinging tentacles from the man o’war and wield them in their tentacles like little whips to ward off predators.