Beachcombers sometimes discover a peculiar, often dark, leathery object washed up by the tide. This intriguing find frequently sparks curiosity about its origin and purpose. This enigmatic item is widely known as a “devil’s purse.”
Unraveling the Mystery
A devil’s purse is an egg case, a protective capsule for the developing embryo of certain marine animals. These cases typically exhibit a rectangular or purse-like shape, often featuring distinct tendrils or horns at each corner. The color usually ranges from a dark brown to black, giving them a hardened, aged appearance.
The texture of these cases is often described as leathery or fibrous, providing a robust outer layer. Their size can vary significantly depending on the species that produced them, ranging from a few centimeters to over 20 centimeters in length. These cases are designed to safeguard new life.
The Ocean’s Architects
These egg cases are laid by specific types of cartilaginous fish, which are characterized by skeletons made of cartilage instead of bone. The primary architects of devil’s purses are skates, but some species of sharks and chimaeras also produce similar egg capsules. These marine inhabitants typically reside on the ocean floor, where they anchor their egg cases to various substrates.
The appearance of the egg case often indicates the species that laid it. For instance, many skate egg cases are identifiable by their four horn-like projections at each corner, which help to secure them to the seafloor. In contrast, some shark egg cases, such as those from horn sharks, exhibit a unique spiral or corkscrew shape, aiding in their wedging into crevices for protection.
Beyond the Beach: A Life Cycle
The egg case provides a safe, enclosed environment for the developing embryo. Within its tough, leathery exterior, the case shields the vulnerable young from predators and the harsh conditions of the ocean environment. Small slits or pores on the case allow seawater to circulate, providing oxygen for the growing embryo.
Inside the case, the embryo is sustained by a large yolk sac, which serves as its primary food source throughout its development. The time required for the embryo to mature and hatch varies by species, ranging from a few months to over a year. Once fully developed, the young marine animal emerges from the case, ready to navigate the ocean waters.
After hatching, the empty, lightweight egg case often detaches from its anchor point and drifts with ocean currents. These discarded cases eventually wash ashore, becoming the “devil’s purses” that beachcombers find. If encountered, leave it undisturbed as a testament to the ocean’s intricate life cycles.