This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Big eyes can be a big benefit—allowing an animal to see potential prey and predators coming from a wider field. For the octopus, this is especially important in the open ocean, where knowing what is around—or above or below—you is crucial for survival.
One type of octopus has taken a different approach to wide-angle vision. Rather than huge peepers, the telescope octopus (Amphitretus pelagicus) has positioned its eyes on top of long, moveable stalks. This vantage point presumably gives the A. pelagicus superb peripheral vision.
Scientists don't know much about this rare pelagic octopus. And the evolution of its bizarre optical organs is largely a mystery. The telescope octopus is closely related to the glass octopus (Vitreledonella richardi), which has moderately elongated eyes. But the telescope octopus is the only known octopod to possess such extreme, protruding eyes.
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Like the glass octopus, the telescope octopus (named for its eye stalks) is largely transparent. It seems to swim with its oblong opaque stomach and eyes aligned vertically, perhaps to reduce its profile that might be seen by predators below.
Its long, gelatinous web extends much of the way down its arms. The arms have sparse white suckers speckled down their length.
These octopuses have been found at a variety of depths—from 150 to 2,000 meters. And it seems to live primarily in tropical and subtropical waters, spending its life swimming in the water column, rather than crawling on the seafloor like most octopus species.
Some researchers have speculated (pdf) that the telescope octopus, the glass octopus and their close gelatinous relatives emerged to live out their full adult lives in an arrested larval-like stage (a phenomenon known as neoteny). Like the larvae and young hatchlings of other octopus species, these octopods stay suspended in the water column and have transparent bodies. As such, they might fill a similar niche to their pelagic cephalopod cousins, glass squid. But, according to DNA analysis (pdf), their closest relatives in the octopus group belong to the Pareledone genus, which live along the cold ocean floors of the Antarctic. The two lines likely split some 33.5 million years ago before more modern ocean currents came into existence. Since then, it seems the telescope octopus hasn't looked back.
Illustration courtesy of Ivan Phillipsen