Carrier Crabs Carry Sea Urchins Around

The daily activities of sea urchins aren't well-known for being very active. They resemble aquatic porcupines and can move about even though it's difficult to detect their tiny feet. If necessary, they can also move by moving their spines. Because they lack eyes but do have mouths and spines, they get along so well with the crab that bears their name, the carrier crab.

The crabs carry things on their backs using two of their legs. They are able to grasp reasonably large objects that they balance on the rear of their shells because of the special adaptations made to these legs for this purpose. The urchin's numerous poisonous spines defend the crab from predators as it moves across the ocean floor. The urchin can consume the leftovers the crab leaves behind when it finds food at the same time. When the crab ultimately lets it go, it will benefit both creatures by being given other eating grounds.