Sea spiders have jointed appendages that serve multiple roles—treading delicately on the seafloor or on water, even housing vital organs. Instead of breathing through gills or lungs, oxygen diffuses through their legs.. With long legs, there is greater surface area for efficient respiration. Their egg-carrying appendages, called ovigers, are just as multi-functional, used for cleaning, courtship, and reproduction.

Sea spiders are carnivores that behave like parasites as they do not kill their prey directly when they feed. They use a long, tube-like mouthpart called a proboscis to pierce soft-bodied prey and draw out nutrient-rich fluids. Dense bristles inside the proboscis filter out solids, making their feeding process surprisingly efficient.

Sea spiders spend their entire lives on the seafloor. This makes them susceptible to the impacts of bottom trawling, where nets are dragged across the seabed. This can damage or destroy their habitats, leaving them with fewer places to live and hide in.