Have you ever seen these on the beach and wondered what they are? They are commonly called mermaid’s purses and they are egg cases. By the time they wash onto the shore they have usually hatched but occasionally they haven’t and then if you hold them up to the light you can see the yolk sac and the little embryo inside!
The one on the right with the ‘horns’ is a skate egg case, they usually only contain one embryo but the eggs of the big skate and mottled skate are considerably larger and can contain up to seven embryos.
The other egg case belongs to a species of shark and the curly tendrils anchor the egg to sea weed.Not all sharks lay eggs but oviparity is common among some of the smaller catsharks, dogfish sharks and bamboo sharks.The majority of sharks are ovoviviparous in that fertilised eggs develop and hatch in utero and then live young are born. The large sharks like the great white and ragged tooth sharks that most of us are familiar with give birth to live youngthat have developed with a placenta (viviparous). In fact the young ragged tooth sharks are cannibals as the mother may have up to ten babies in utero but the largest ones eat the smaller ones until there are only two left to be born!
