The Cucumber That Walks
The sea pig (Scotoplanes globosa) is not a pig, but a type of sea cucumber that lives on the abyssal plains of the world's oceans, often at depths between 1,000 and 6,000 meters. Its common name comes from its pinkish body, which grows to between 5 and 15 centimeters long. This gelatinous body is an adaptation to the pressure of the deep sea. The Swedish scientist Hjalmar Théel first described the species in 1882, following its discovery during the HMS Challenger expedition between 1873 and 1876.
Unlike most other sea cucumbers, Scotoplanes is known for its unique method of "walking." It moves across the soft seafloor on five to seven pairs of large, leg-like appendages. These are not true legs, but enlarged tube feet powered by a water vascular system. By contracting its muscles, the sea pig can push water into and out of these "legs," inflating and deflating them to waddle through the mud. It also has sensory papillae on its back that look like antennae and help it detect chemical signals in the water.
A Dominant Deep-Sea Janitor
In the complete darkness of the abyss, where temperatures hover between 2 and 4°C, the sea pig is a dominant life form. In some regions of the deep sea, these creatures make up over 95% of the total weight of animals on the seafloor. They are deposit feeders, using a ring of mucus-covered tentacles around their mouths to scoop up the top layer of sediment. Their diet consists of "marine snow"—a constant shower of organic detritus and waste that falls from the sunlit waters far above. They show a strong preference for freshly fallen material, less than 100 days old, which is more nutrient-rich.
Sea pigs are often found in large groups, sometimes numbering in the hundreds. These congregations frequently face the same direction, oriented into the current. This behavior likely helps them detect the scent of new food sources, such as the massive boon provided by a whale carcass that has fallen to the seafloor. By constantly churning up the sediment, they help recycle nutrients in the deep-sea ecosystem. Few predators bother them, as their skin contains a toxic chemical called holothurin. However, they are often hosts to parasites like small snails that bore into their body wall.