Zoom Sharks SHARK ANATOMY

Unlike most bony fish, shark's eggs are fertilized inside the female's body. The male shark has "claspers," extensions of the pelvic fins that are used to transfer sperm to the female and fertilize her eggs.

Most sharks give birth to live young, but some release eggs that hatch later. The gestation period (the time the embryo spends inside the female, developing) can be up to almost two years long (the spiny dogfish shark may have the longest shark gestation period).

Baby sharks (called pups) are born with a full set of teeth and are fully ready to take care of themselves. They quickly swim away, even from their mothers who might eat them. Litter size ranges from one or two pups (for a great white shark) to over 100 (for a large blue shark and the whale shark).

There are different types of shark egg development:

• Viviparity- The eggs hatch inside the female's body and the babies are fed by a placenta which transfers nourishment from the mother to the babies (via an umbilical cord which is connected to the baby shark behind the between the pectoral fins). The placenta helps transfer nutrients and oxygen from the mother's bloodstream and transfers waste products from the baby to the mother for elimination. Viviparous sharks give birth to live young. The number of pups in a litter ranges from 2-20 or more. Examples of viviparous sharks include the Bull sharks, Whitetip reef shark, Lemon shark, Blue shark, Mako, Porbeagle, Salmon shark, the Silvertip shark, and Hammerheads. Although long thought to be oviparous (an egg 14 inches (36 cm) long was once found), Whale sharks are viviparous and pregnant females have been found containing hundreds of pups.
• Oviparity- These sharks deposit eggs in the ocean which will hatch later if they are not eaten by predators. The eggs are not guarded by either parent. Shark eggs (sometimes called "mermaid's purses") are covered by a tough, leathery membrane. Their shape ranges from pouch-like to screw-shaped (like the California hornshark and the Port Jackson shark). Some eggs (like those of catsharks) have tendrils that attach the egg to objects on the sea bed. The egg has a yolk that feeds the embryo, very much like a chicken egg. Oviparous sharks include the Zebra shark, the catsharks, swellshark, the necklace carpetshark, some Epaulette sharks, and the Hornshark.
• Aplacental Viviparity (Ovoviviparous)- In these animals, the eggs hatch and the babies develop inside the female's body but there is no placenta to nourish the pups. The pups eat any unfertilized eggs and each other (they are oviphagous). Very few pups in a litter survive until birth due to this form of sibling cannibalism. Great white sharks, sawsharks, Mako, crocodile sharks, Cookiecutter sharks, Pelagic thresher, Greenland shark, Gummy shark, Soupfin shark, Pacific Angelshark, Pygmy sharks, Nurse shark, Tiger shark, and Sand tiger sharks reproduce this way.

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