For more than a million years, sharks are the marine species that have gone through the evolution to evolve as the most efficient fish for their perfect role at the top of the food chain in the marine ecosystem. You may have seen Jaws in a movie, but have you ever wondered about other bizarre looking and amazing sharks that live on our planet?
Over 350 million years ago, that was before the existence of the dinosaurs, sharks already existed in most of the waters in the world. They are many varieties of sharks with about 368 different species of them being known. They include bull shark, whale shark, and hammerhead sharks, to name a few of them.
Sharks, basically, are boneless and their skeleton is mainly made of cartilage which is as hard as bones, and their skeleton is just like their vertebrae and is calcified. They have many varieties of body shapes, with some of them having an elongated body shape. At one time, sharks could have up to 3,000 teeth but they are of little use since most sharks prefer to gulp down their prey in large pieces instead of chewing their food.
Saw sharks (or Pristiophoriformes) have long blade-like snouts edged with teeth resembling a saw, which they use as a useful tool to disable and even slash their prey. They can grow up to 5m in length, and the Japanese saw shark (Pristiophorus japonicas), the Bahamas saw shark (Pristiophorus schroederi), and the long nose shark (Pristiophorus cirratus) are some of the identified species which can be found in waters from South Africa to Australia and Japan. Like other sharks, they have gills on each side of the neck and they feed on squids, crustaceans, shrimps and bony fish.
Spined Pygmy Sharks
Having a spine in front the first dorsal fin, Spined Pygmy sharks are one of the smallest uncommon sharks averages 7 to 8 inches ( or 18-21cm) long with males average about 7 inches (=18cm long) and females reaching maximum length of just 8 inches. They are found inhabiting primarily in deep water down to 2,000 m but they migrate vertically to the mid-depth waters of 200 m each day to hunt for food. As they have bio-luminescence (or luminous photophores) positioned on their bellies running along their midsection, they can blend easily with ambient light conditions, and be camouflaged from both prey and predators.