aquatic egg cases (not mine)

seen from Australia
seen from Bangladesh

seen from Germany
seen from Japan
seen from Germany
seen from France
seen from Canada
seen from Germany

seen from Germany
seen from Germany
seen from China
seen from China

seen from Canada
seen from Germany
seen from Germany
seen from United States
seen from China
seen from Germany

seen from Canada
seen from Sweden
aquatic egg cases (not mine)
© Peter Arkle 2023 TEN MERMAID’S PURSES
Mantis egg cases
Hildacy Farm Preserve, Upper Providence, Pennsylvania
Dec. 27, 2016
When sharks lay egg cases in the shark and ray touch tank
Empty... by Sea Moon on Flickr.
Shark egg You can see the hatchling moving inside.
Learn more about shark reproduction at the New England Aquarium, including photos of baby sharks and details about the egg cases.
(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)