#devil's purse

[oceansoftheworld]

(Photo by David Doubilet)

Blotchy swellshark in its egg, or mermaid’s purse.

[oceansoftheworld]

(Photo found here)

Unlike most bony fish, which shed hundreds or even thousands of unprotected eggs into the water, cartilaginous fish (Chondrichthyes) produce only a few young and protect them inside a leathery egg case. Most female sharks keep the egg case inside their bodies and give birth to live young. Skates, rays and some types of sharks, however, lay a couple of egg cases on the ocean floor and leave them to develop alone. The egg cases are colloquially known as a mermaid's purse or devil's purse. They are commonly found washed up by the sea. The egg cases that wash up on beaches are usually empty. Furthermore, egg cases are often found in commercial fishing gears like nets and pots, and on the sea floor during surveys using an ROV. The size of egg cases vary. The colors and shapes of egg cases also vary greatly from species to species.

(Source)