Mermaids are either notoriously bad with their money and regularly lose their belongings or something else is happening beneath the waves that results in mermaid’s purses being commonly found along our beaches. Whilst they often appear empty, these small pockets that look similar to seaweed hold a secret.
The mermaid’s purse starts to reveal some of its mystery when we consider that the common Afrikaans name for them is “haai-eiers” or shark eggs, more specifically egg cases of some sharks, skates and chimaeras. These are Chondrichthyes, a class that contains cartilaginous fishes that have skeletons primarily composed of cartilage, not bone.
It is extremely important to note that not all sharks lay eggs. Some, like the Great White Shark, have eggs which hatch inside the female’s uterus and they then give birth to live young, whilst others like the Bull Shark have young attached to umbilical cords and give birth to live young like most mammals.
All skate, all chimaera and some shark species like catshark and shysharks are oviparous (egg layers). Like birds, each species has a specific egg colour and shape, so it is possible to determine the species each egg comes from. Fertilized eggs are deposited onto the sandy bottom or in the case of sharks they are attached to seaweed or rocks. The egg capsule/purse which is made of protein contains the embryo, which feeds on yolk until it is ready to hatch.
When one finds an empty egg case washed up on shore they can easily be classified into three major groups by shape. Chimaera egg cases have a very distinct teardrop-like shape and broad lateral keels, while in the case of the St John’s Fish the egg case looks somewhat hairy.
Catshark/Shyshark egg cases are more rectangular in shape and have curly tendrils on their corners which are used to anchor the egg in place.
Skate egg cases are mostly square in shape and have horns (rather than tendrils) attached to all four corners.
Further identifying the egg cases to a species level is trickier and requires some practice; identification guides are available on the internet if one searches “shark eggs South Africa”. The next time you find a mermaid’s purse, why not try to identify what species it came from and reveal some of our ocean’s secrets for yourself?