Shallow-water octopuses can be difficult enough to find. They camouflage against corals, hide in holes and generally make themselves scarce. But researchers can at least attempt to observe and collect them by snorkeling, diving or skimming nets and bottom trawls.

The rest of the vast, dark ocean, however, presents a much larger sampling challenge. So when it comes to the many octopus species that live in the deeper seas, we know next to nothing.

And yet these cephalopods represent an important element in the world's oceans—not just for documenting biodiversity, but also for understanding the nuanced and complex underseas relationships and food webs. "Pelagic cephalopods are some of the main faunal components of the oceanic ecosystems," wrote the authors of a review paper published recently in Mediterranean Marine Science. They eat a lot—and get eaten by a lot of larger animals. Nevertheless, "they are also some of the most poorly understood."

In the coming posts, we will explore what we do know about some of these more mysterious octopuses—and how science is struggling to learn more about them.

Today's subject: the football octopus.

Not to be confused with Paul, the purportedly psychic octopus that predicted outcomes in the 2010 World Cup (which was an Octopus vulgaris), the football octopus (Ocythoe tuberculata) is a species unto itself.

Originally described in 1814 by the eccentric zoologist and Constantinople native Constantine Samuel Rafinesque-Schmaltz, O. tuberculata is the only formally recognized species in its family. It is thought to live primarily in subtropical and tropical waters, from the southern Atlantic near Namibia to the Pacific near Japan. Unlike the better-known benthic octopus breeds, these animals live most of their lives in the sunlit zone of the open ocean. They seem to come even closer surface-ward at night, perhaps to feed. They have four shorter arms and four longer ones, giving them an uneven appearance. Rare among cephalopods, the football octopus has a gas-filled swim bladder, which lets it easily control its position in the water column like many fish do.

It is also one of the most fecund octopuses known to science and one of the few thought to hatch live young [pdf]. A female specimen found in 2010 (by Salman and Akin) had somewhere around one million eggs—a record for the octopus world. This individual was also the largest known for her species (with a body length of 33.5 centimeters). Reports of males are even more rare, but they are puny in comparison, measuring in at about of a tenth of the body length.

The recent review paper, which was published online in February, took stock of scientific samples, fishery finds and stranding reports recorded in the octopus-rich Mediterranean over the course of 16 years (from 1994 to 2010).

The researchers, led by Antoni Quetglas, of Spanish Institute of Oceanography, found just two reports of football octopuses (also known by the less memorable name tuberculate pelagic octopus) since the mid 1990s. One was caught in a net during a scientific survey off the northeastern coast of Spain at a depth of 115 meters. It weighed a hefty 1.3 kilograms. The second was landed by a fishing ship off the coast of Spain's southern Balearic Islands. It weighed an even meatier 1.5 kilograms and had arms that extended longer than 42.5 centimeters.

Other occasional reports of O. tuberculata come from fishing boats—and the sampling of the stomachs of their predators, such as swordfish and yellowfin tuna. One 2009 report [pdf], published online in JMBA2-Biodiversity Records, describes two live football octopuses caught by bait off of the northwestern Atlantic coast of the Iberian Peninsula in the summer of 2006. The surprisingly northern location of the catches was attributed to warmer-than-average sea temperatures that month.

Next up: the deep-sea cirrate octopus Opisthoteuthis calypso.

Illustration courtesy of Ivan Phillipsen