Rays, chimeras, skates, and some species of sharks create an egg case that is colloquially known as a mermaid's purse. Can you eat shark eggs? Yes, you can — from certain species. They are considered a delicacy.
The egg is a capsule that contains a developing animal and a yolk sac which the young gets its nutrition from. A capsule usually houses one embryo, but in some species there are multiple embryos per egg case. Some cases have long tendrils that help them to attach to seaweed or rocky seafloors.
Sharks that lay eggs
Oviparity – the laying of eggs – is harnessed by a small number of shark species, as most sharks are viviparous, meaning the eggs develop inside the mother. These often palm-sized eggs come in various colours, shapes and textures, depending on the species of shark.
About 40% of shark species, and all species of skates, lay eggs. Also called mermaids purses, the egg cases are usually attached to substrate, such as kelp or rocks, and the embryos are nourished from a yolk sac until it has all been absorbed and they push their way out into the world as fully-formed young.
Port Jackson Sharks are oviparous, which means that the female lays eggs. The egg case is a tough, dark brown spiral about 7 cm to 8 cm wide and 15 cm long. It is common to see them washed up on beaches.
If a live embryo is inside, put the eggcase back in the sea or a deep rockpool and try to anchor it down. If it is a skate eggcase try and weigh down the horns, with catshark eggcases try and tie the tendrils around something so it doesn't wash ashore again. Empty eggcases are not known to have any secondary purpose.
As she held up the horn shark corkscrew egg casing, she explained what it looked and felt like. "It looks like glass, I know, but no, they're actually soft and the case itself is pretty squishy."
Unlike chicken eggs, shark eggs are encased in a leathery, watertight shell designed to keep baby in and predators out. That leather shield is especially important because mother sharks tend to swim away from their young after laying them, leaving their progeny to fend for themselves from the very beginning.
In sharks, asexual reproduction commences via a birth mechanism dubbed 'automictic parthenogenesis'. It's a form of self-fertilisation that somehow mimics sexual reproduction.
Many shark eggs are preyed on by marine snails called gastropods. One of the prime culprits in this group of animals is the whelk, a predatory snail that bores holes into its prey to slurp out the nutritious innards.
Egg-laying sharks
Usually the eggs are quite large, 5 to 25 cm long. They contain a lot of yolk to ensure that the embryos are richly supplied with nutrients. Depositing the young animals in well-protected, stable egg shells with sufficient nutrients shortens the time a female shark is pregnant.
Ovoviviparity: Most sharks are ovoviviparous; they combine the first two methods. They produce eggs, but instead of hatching outside the body as in oviparity, the eggs are carried within the female for the gestation period. When the egg hatches, the shark pup continues developing inside the female until it's born.
Clutch size: One egg recovered from a whale shark measured an astonishing 30 cm (12 in.) long, 14 cm (5.5 in.) wide, and 9 cm (3.5 in.) thick - making it the biggest egg of any animal ever recorded.
Whale shark eggs
Whale sharks are ovoviviparous, which means the eggs hatch inside the female's body and the young are then born as miniature adults. Of all the egg-producing sharks, whale sharks produce the largest eggs.
Each shark egg-case holds one embryo (the egg-cases of some skates hold multiple embryos). Sharks such as the lesser spotted dogfish (also known as the small spotted catshark) lay around 20 eggs each year. Shark egg case, or mermaid's purse, attached to red tree coral.
Set the shark meat in a refrigerator-safe dish and submerge it in milk. Allowing it to soak eliminates the smell of ammonia and gamey flavor that a lot of fresh catches have.
Some sharks such as the nurse shark have spiracles that force water across their gills allowing for stationary rest. Sharks do not sleep like humans do, but instead have active and restful periods.
Many sharks are viviparous, meaning they give birth to live young. Like all sharks, species such as blue, bull, and hammerhead sharks rely at first on a yolk sac for nutrition. But they also develop a placental connection similar to a mammal's umbilical cord.
The eggs are fertilized internally and laid in a mermaid's purse, a protective case that keeps the eggs safe while the embryo develops. The egg case may attach to the ocean floor or wash up on shore.
So the largest underwater egg is seen in whale shark and the largest land egg is seen in the ostrich.
The best place to look for egg cases is within the strandline – the seaweed washed up at the top of the shore. Some may also be blown into the crevices between rocks at the top of the beach. They are well camouflaged so keep your eyes peeled!
The shark eggs have spiral ridges on their outer layer which helps them grip better to rock crevices. The mother shark screws the egg into rock crevices and nook which prevents the eggs from getting washed away by waves. It also protects in from predator attacks.
Bullhead shark egg cases are shaped like an auger, with two spiral flanges. This allows the egg cases to become wedged in the crevices of rocky sea floors, where the eggs are protected from predators; however, some bullhead sharks deposit their eggs on sponges or seaweed.
OVIPARITY (egg-laying)
It can take between 6-9 months before they're ready to hatch. Depending on the species, features such as curled tendrils, horns and sticky mucus filaments attach the eggcase to a substrate. This can be the seabed, reef or seaweed.