Skate egg cases
The Skate is a wide, flattish, non-bony fish which has “wings” or fin-type projections on the sides of its body. The Skate is almost as wide as it is long, and has a whiplike tail which it uses as a rudder. It can weight up to 100lbs. It is related to the Stingray, and is a bottom feeder, where it eats crabs and other crustaceans, worms, bivalves, and small fish. The Skate itself is a food source for humans.
The Skate egg case is a small (3-4 inches long), leathery, rectangular sort of pouch with long, thin, horn-like projections sticking out from each corner. The egg cases are made of keratin, the same substance of which human fingernails are composed. An egg case forms around each individual skate embryo just before the mother deposits the cases on the sea floor.
The long, curved projections on each corner of the egg case are covered with a gummy material. The “horns” tend to catch on seaweed or other objects, helping to anchor the egg case to the bottom. The horns serve to extract oxygen from the water, and to release waste back into the water. The egg cases are very tough and hard to penetrate, thus detering predators.
Interestingly enough, initially the egg cases are waterproof because the embryos do not have gills until after three weeks of development. Then small holes open in the tips of the horns, admitting seawater, and the baby learns to live as an underwater creature.
When the time comes for the young skate to escape its natal confinement (anywhere from 3-15 months), the egg case splits open at one end and the youngster emerges.
Empty egg cases may wash up on the beach. These dark, blackish containers are sometimes called “devil's pocketbook” or “devil's purses;” “mermaid's purses;” or “sailor's purses.”