For beachcombers, discovering a “mermaid purse” often sparks curiosity about its origin. These distinctive objects, found washed ashore, are not mythical treasures but protective egg cases of certain marine animals. They serve as nurseries for developing young, offering a glimpse into the reproductive strategies of some of the ocean’s ancient inhabitants.
Identifying a Mermaid Purse
Mermaid purses vary in physical characteristics depending on the species. They are typically leathery, ranging from black to dark brown or green when dried. Shapes are often rectangular or pillow-shaped, though some are spindle-shaped with feathery fins. A distinguishing feature is the tendrils or horns at each corner, which can be long and curly or shorter spikes. These cases are composed of tough, flexible collagen protein strands.
Most mermaid purses found on the beach are empty, flattened, and dried out, indicating the young has already hatched. If a case is plump and translucent, it might contain a developing embryo. The specific size and shape of these features, including tendrils and the capsule, can help identify the species.
The Creatures Behind the Case
Mermaid purses are produced by specific cartilaginous fish, primarily certain sharks, skates, and chimaeras. While many shark and ray species bear live young, smaller sharks like catsharks and all skates are oviparous, laying eggs in these protective structures. Chimaeras, also known as ratfish or ghost sharks, also produce distinct egg cases.
The egg case provides a secure, self-contained environment for the developing embryo. It shields the vulnerable young from predators and harsh conditions. The embryo uses the yolk sac for nutrients and may undulate its tail to circulate oxygen-rich water through small slits. This design ensures the offspring’s survival until it emerges as a miniature adult.
Finding and Understanding Mermaid Purses
Mermaid purses are commonly found washed ashore on beaches, especially along the high tide line with other debris. Their unique shapes and tendrils serve an important ecological purpose. The tendrils or horns act as anchors, allowing the female to secure the egg case to underwater structures like seaweed, kelp forests, or the seafloor, preventing them from being swept away. For example, skate egg cases often have shorter horns for anchoring to soft sediments, while catshark cases have longer, curly tendrils for entanglement with seaweed.
If an intact, possibly viable, mermaid purse is found, it is generally advised to observe it without disturbing it. If found out of water, return it to a calm, shallow part of the ocean, ideally anchored to seaweed or rocks. Reporting sightings to local aquariums or citizen science initiatives can contribute valuable data to marine biologists, helping map nursery areas and support conservation efforts.