Vast expanses of sea ice make the Arctic and Antarctic oceans perilous and inhospitable, but they’re also vital guardians of Earth’s climate.

Sea ice forms when ocean water is cooled to the freezing point by cold polar air. Freezing begins in fall, when the amount of light from the sun decreases, and ice continues to expand and thicken during the dark winter months. When summer returns, the sun’s energy warms the surface of the ice, causing portions of it to melt.

You might imagine marine snails crawling around on the sea floor. But thanks to a unique adaptation, one family of snails lives life at the top of the ocean.

Violet snails cannot swim but they can construct “rafts” from clusters of air bubbles, and these rafts allow the snails to float at the water’s surface. They float throughout tropical and subtropical oceans, preying on an abundant food source − jellyfish.