sea purse
/ˈsiː ˌpɜːrs/
noun
- The egg case of a skate or some sharks, often found washed up on beaches; also called a mermaid's purse.
- A sea-purse is a leathery capsule that protects the developing embryo.
- Marine biologists study sea-purses to learn about shark reproduction.
- The children found a sea-purse on the sand and thought it was a strange seed pod.