What common name is given to the egg cases of many oviparous sharks and rays?

The common name for the egg cases of many oviparous sharks and rays is “mermaid’s purse.”

These leathery capsules, also called egg cases or egg capsules, are made largely of collagen. They protect developing embryos after the female deposits them on the seafloor, among rocks, or in kelp. Their familiar rectangular shape often includes horn-like projections or tendrils that help anchor the case.

A mermaid’s purse is not a single species or even exclusively a shark structure. Skates and some chimaeras also produce egg cases, and most contain one embryo. The big skate and mottled skate are notable exceptions, with cases that can hold several embryos. During development, slits open in the capsule so water can flow through, while the embryo’s tail helps maintain circulation.

The term can cause confusion because many shark species give birth to live young instead. Blue sharks, for example, are viviparous, whereas egg-laying carpet sharks and many skates use protective capsules. Once empty, these cases often wash ashore and are mistaken for seaweed or unusual shells.