Wednesday, February 9, 2011

Tremoctopus, The Blanket Octopus

Recently Pharyngula had a link to a rather interesting video of a rarely seen octopodian, the Blanket Octopus. However, neither the video nor Pharyngula went into detail about this unusual mollusk so I thought I would take the time to write a bit more about it.

Blanket Octopus is the common name for the four known species of cephalapod within the genus Tremoctopus. All are pelagic (open ocean) species found in sub-tropical and tropical oceans. They get their name for the defensive display of the females. Upon being startled, the female will unfurl a long draping membrane that connects the larger arms. This drastically increases the size of the animal and along with its bright colors, is often enough to dissuade many would be predators.

A female blanket octopus with her arms curled into her mantle.

Ostentatious is a word the Blanket Octopus is not familiar with

Another feature of note in this genus is the high degree of sexual dimorphism. The males never develop the elaborate display of the females nor do they achieve their size. Females commonly attain the length of 2 meters where as the males are only a few centimeters at most. The males can only mate once, where upon they detach a specialized arm known as the hectocotylus which then crawls into the females mantle to fertilize her eggs. Upon delivering the hectocotylus, the male swims away to die. The female is then left to carry her 100,000 eggs at the base of her dorsal arms where they remain until hatching.

Only discovered in 2003, the male Blanket Octopus is up to 100 times smaller then the female.

Another interesting defensive behavior has been seen in both males and juvenile females. They are often seen drifting with Portuguese Man o' Wars for protection. When threatened, they will often start tearing apart the jelly leaving a cloud of armed tentacles in its wake. Occasionally they will go so far as wielding broken tentacles as defensive armaments. The octopus is never harmed as they are utterly immune to the Man o' Wars venom.
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