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LOW-CALORIE DIET

A “seven-armed” octopus has been caught eating jellyfish

Akshat Rathi
By Akshat Rathi

Senior reporter

Scientists know less about the bottom of our oceans than they do about the surface of Mars. That’s why, every time they catch a glimpse of life in the deep seas, they are often surprised by what they see.

The latest discovery regards a rare cephalopod, Haliphron atlanticus, a “seven-armed” octopus. It gets this name because it keeps its eighth arm tucked in a sac under its eye. In a 2013 expedition, scientists used a remote-controlled submersible to spot the octopus—only the third such sighting of the unusual creatures, which can grow to be 4 meters (12 feet) long.

What was particularly surprising, though, was what the researchers saw the octopus eating: an egg-yolk jellyfish (Phacellophora camtschatica).

Scientists have long thought of the jellyfish as a “nutritional dead-end,” which implies that predators get little reward from the potentially risky hunt of the gelatinous ocean dwellers. The seven-armed octopus’s breakfast suggests that jellyfish may make good meals after all.

To confirm that they were not witnesses to a one-off craving, scientists from the Helmholtz Centre for Ocean Research in Germany and the Monterey Bay Aquarium Research Institute looked at preserved museum specimens of H. atlanticus and found remnants of jellyfish in every stomach. Their study was published this week in Scientific Reports.

H. atlanticus, like other deep-sea creatures, can’t afford to be picky when it comes to food. That’s why they tend to have low metabolism rates which, in effect, make their body clock run slowly. Thus, eating low-calorie jellyfish may provide enough nutrition to keep them going. The more scientists look at cephalopods, the more they learn about the mysterious lives they lead.