Glass octopus in the Atlantic Ocean off Cabo Verde

© Solvin Zankl/Minden Picture

See-through cephalopod

One of the least understood of sea creatures, this glass octopus lives in the depths of the ocean where sunlight can't reach, about 900 metres down. Glass octopuses are rarely seen and difficult to observe, but they're a great example of the diversity of the order Octopoda, which we're celebrating today on World Octopus Day. The observance comes around, appropriately, every October 8.

The more we learn about octopuses, the more fascinating they reveal themselves to be. They’re among the most intelligent and behaviorally dive…..