What is a mermaid's purse?

Mermaid's purses are the protective cases in which the eggs of dogfish, skates, and rays are released into the environment. The rectangular purse is leathery and has long tendrils streaming from each corner. The tendrils anchor the case to seaweed or rocks and protects the embryos during the six to nine months it takes for them to hatch. Empty cases often wash up on beaches.

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