The seven-arm octopus, Haliphron atlanticus, weighs as much as a person and haunts deep, dark waters from New Zealand to Brazil and British Columbia. So few people have seen this creature alive that researchers must study it in death--typically, as a mound of purplish flesh that washes ashore or turns up in a net. A living seven-arm octopus was scooped up by a Norwegian fishing trawler in 1984, but "when laid on deck the body collapsed," a local zoologist wrote at the time. What remained of the creature, he added, was "sack-shaped, large and flappy." Another turned up in a South Pacific research trawl in the early two-thousands, but the preservation process turned it into a "frozen lump," the giant-squid expert Steve O'Shea wrote.

A strange sea creature that lives 1,000 feet below the surface encased in a giant bubble of mucus may be key to removing carbon dioxide from the atmosphere. These bubble-houses are discarded and replaced regularly as the animal grows in size and its filters become clogged with particles. Once discarded, they sink to the seafloor and encapsulate the carbon for good, preventing it from re-entering the atmosphere. Larvaceans also capture and dispose of microplastics in this way, which can come from clothing and cosmetics and often ingested by other marine species. Researchers used a system of lasers mounted on a 12,000 pound robot to map the giant larvacean's delicate body in a series of 3D images.