Unusual Offshore Octopods: The See-Through "Glass" Octopus [Video]

Scientific American
Unusual Offshore Octopods: The See-Through "Glass" Octopus [Video]
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Glass octopus courtesy of R. Larsen/Fish and Wildlife Service/R. Harbison, Woods Hole Oceanographic  …

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Octopuses that live in the deep open ocean are difficult enough to find. But try locating a "glass" octopus, which is nearly transparent. Floating in the dim midwaters, this gelatinous octopod looks almost like a be-suckered jellyfish.

Rather than camouflaging like most known octopus species, the Vitreledonella richardi has taken this alternative approach to hide from potential predators--and perhaps from prey as well. Its translucent body helps it remain less visible, especially when it is near the upper reaches of its habitat, around 300 meters, where some light still penetrates. (Some specimens, however, have been caught nearly 1,000 meters below the surface.) Only sparse red chromatophores (which appear black in such dark environments) color their flesh.

The glass octopus's unusual appearance makes for a rare view inside these elusive animals. Photos taken from the deep show the opaque digestive organs and optic nerves. Its small suckers stand out as white adornments in the bright light used to film them.

Many octopus species have large, round eyes, which help increase their field of vision. The glass octopus, however, has oddly elongated eyes. This tubelike structure shrinks their peripheral vision, but it might keep them from being spotted from below, according to research published in the Journal of the Marine Biological Association of the United Kingdom. The tradeoff must be worth it. The eyes also seem to be pointed perpetually upward, toward the dim light above, according to vision researcher Michael Land, of the University of Sussex.

Because these octopuses are so rarely captured--physically or on film--little is known about their lifecycles and their habits. They seem to grow up to about 45 centimeters in total length from a hatchling size of about 2.2 millimeters.

Many octopuses that have to mate in the open seas have a detachable limb (a hectocotylus) that the males use for fertilizing the female. But the glass octopus is not so gentle. One stunning video, shot off the coast of Hawaii at about 900 meters below the surface, shows two glass octopuses in what is presumed to be a strange mating posture--with one inside the ample web of another.

And because they live in the open water with no burrows, the females seem to carry their hundreds of eggs with them until they hatch.

http://www.youtube.com/watch?v=XHHwPqPPapc

Video courtesy of R. Larsen/Fish and Wildlife Service/R. Harbison, Woods Hole Oceanographic Institution/YouTube

Illustration courtesy of Ivan Phillipsen

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