Sharks are a group of fishes characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Since that time, sharks have diversified into over 400 species. Despite its size, the whale shark feeds only on plankton, squid, and small fish by filter feeding.
Sharks are found in all seas and are common down to depths of 2,000 meters (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark that can survive in both seawater and freshwater.
They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They also have several sets of replaceable teeth.
Well-known species such as the great white shark, tiger shark, blue shark, mako shark, and the hammerhead shark are apex predators—organisms at the top of their underwater food chain. Their predatory skill fascinates and frightens humans, even though their survival is threatened by human-related activities. In this post I will share you 5 most unbelievable sharks around the earth.
The goblin shark, Mitsukurina owstoni, is a deep-sea shark, the sole living species in the family Mitsukurinidae. The most distinctive characteristic of the goblin shark is the unusual shape of its head. It has a long, trowel-shaped, beak-like rostrum or snout, much longer than other sharks’ snouts.
Some other distinguishing characteristics of the shark are the color of its body, which is mostly pink, and its long, protrusible jaws. When the jaws are retracted, the shark resembles a pink grey nurse shark, Carcharias taurus, with an unusually long nose.
Mitsukurina owstoni is found in the deep ocean, far below where the sun’s light can reach at depths greater than 200 m. They can be found throughout the world, from Australia in the Pacific Ocean to the Gulf of Mexico in the Atlantic Ocean. They are best known from the waters around Japan, where the species was first discovered.
Goblin sharks feed on a variety of organisms that live in deep waters.
Among some of their known prey are deep-sea squid, crabs and deep-sea fish. Very little is known about the species’ life history and reproductive habits, as encounters with them have been relatively rare. As seemingly rare as they are however, there seems to be no real threat to their populations and so they are not classified as endangered species by the IUCN.
The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a “hammer” shape called a “cephalofoil”. Most hammerhead species are placed in the genus Sphyrna while the winghead shark is placed in its own genus, Eusphyra.
The nine known species range from 0.9 to 6 m (3.0 to 20 ft) long and weigh from 500 to 1000 pounds. They are usually light gray and have a greenish tint to them. Their bellies are white which allows them to be close to the bottom of the ocean and blend in to sneak up on their prey. Their heads have lateral projections which give them a hammer-like shape.
It was determined recently that the hammer-like shape of the head may have evolved (at least in part) to enhance the animal’s vision. The positioning of the eyes, mounted on the sides of the shark’s distinctive hammer head pointing outward like a trex, give the shark good binocular vision, as well as 360-degree vision in the vertical plane, meaning they can see above and below them at all times.
The shape of the head was previously thought to help the shark find food, aiding in close-quarters maneuverability and allowing sharp turning movement without losing stability. However, it has been found that the unusual structure of its vertebrae was instrumental in making the turns correctly, more often than the shape of its head, though it would also shift and provide lift.
From what is known about the Winghead shark, it would appear that the shape of the hammer-head has to do with an evolved sensory function. Like all sharks, hammerheads have electroreceptory sensory pores called ampullae of Lorenzini. By distributing the receptors over a wider area, hammerheads can sweep for prey more effectively.
These sharks have been able to detect an electrical signal of half a billionth of a volt. The hammer also allows the nostrils to be placed farther apart, increasing its ability to detect chemical gradients and localize the source.
Hammerheads have disproportionately small mouths and seem to do a lot of bottom-hunting. They are also known to form schools during the day, sometimes in groups of over 100. In the evening, like other sharks, they become solitary hunters.
Many, not necessarily mutually exclusive, functions have been proposed for the cephalofoil, including sensory reception, maneuvering, and prey manipulation. Hammerheads are found worldwide in warmer waters along coastlines and continental shelves.
Unlike most sharks, hammerheads usually swim in schools during the day, becoming solitary hunters at night. Some of these schools can be found near Malpelo Island in Colombia, Cocos Island, off Costa Rica, and near Molokai Island, in Hawaii. Large schools are also seen in southern and eastern Africa.
The megamouth shark, Megachasma pelagios, is an extremely rare species of deepwater shark. Since its discovery in 1976, only a few megamouth sharks have been seen, with 54 specimens known to have been caught or sighted as of 2012, including three recordings on film. Like the basking shark and whale shark, it is a filter feeder, and swims with its enormous mouth wide open, filtering water for plankton and jellyfish.
The appearance of the megamouth is distinctive, but little else is known about it. It has a brownish-black color on top, is white underneath, and has an asymmetrical tail with a long upper lobe, similar to that of the thresher shark. The interior of its gill slits are lined with finger-like gill rakers that capture its food.
A relatively poor swimmer, the megamouth has a soft, flabby body and lacks keels.
Megamouths are large sharks, able to grow to 5.5 metres (18 ft) in length. Males mature by 4 metres (13 ft) and females by 5 metres (16 ft). Weights of up to 1,215 kg (2,680 lb) have been reported.
As their name implies, megamouths have a large mouth with small teeth, and a broad, rounded snout, causing observers to occasionally mistake megamouth for a young orca. The mouth is surrounded by luminous photophores, which may act as a lure for plankton or small fish.Their mouths can reach up to 1.3 metres wide.
It is distinctive for its large head with rubbery lips. It is so unlike any other type of shark that it is classified in its own family Megachasmidae, though it has been suggested that it may belong in the family Cetorhinidae of which the basking shark is currently the sole member.
The whale shark, Rhincodon typus, is a slow-moving filter feeding shark and the largest extant fish species. The largest confirmed individual had a length of 12.65 metres (41.50 ft) and a weight of more than 21.5 tonnes (47,000 lb), and there are unconfirmed reports of considerably larger whale sharks.
This distinctively-marked fish is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhiniodon and Rhinodontidae before 1984), which belongs to the subclass Elasmobranchii in the class Chondrichthyes. The species originated about 60 million years ago.
The whale shark is found in tropical and warm oceans and lives in the open sea with a lifespan of about 70 years. Although whale sharks have very large mouths, as filter feeders they feed mainly, though not exclusively, on plankton, which are microscopic plants and animals.
However, the BBC program Planet Earth filmed a whale shark feeding on a school of small fish. The same documentary showed footage of a whale shark timing its arrival to coincide with the mass spawning of fish shoals and feeding on the resultant clouds of eggs and sperm.
The species was distinguished in April 1828 after the harpooning of a 4.6 metres (15.1 ft) specimen in Table Bay, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Town, described it the following year. The name “whale shark” comes from the fish’s physiology, being as large as many whales and also a filter feeder like many whale species.
The cookiecutter shark (Isistius brasiliensis), also called the cigar shark, is a species of small dogfish shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from as deep as 3.7 km (2.3 mi). It migrates vertically up to 3 km (1.9 mi) every day, approaching the surface at dusk and descending with the dawn.
Reaching only 42–56 cm (17–22 in) in length, the cookiecutter shark has a long, cylindrical body with a short, blunt snout, large eyes, two tiny spineless dorsal fins, and a large caudal fin. It is dark brown in color, with light-emitting photophores covering its underside except for a dark “collar” around its throat and gill slits.
The name “cookiecutter shark” refers to its feeding habit of gouging round plugs, like a cookie cutter, out of larger animals. Marks made by cookiecutter sharks have been found on a wide variety of marine mammals and fishes, as well as on submarines, undersea cables, and even human bodies.
It also consumes whole smaller prey such as squid. Cookiecutter sharks have adaptations for hovering in the water column and likely rely on stealth and subterfuge to capture more active prey. Its dark collar seems to mimic the silhouette of a small fish, while the rest of its body blends into the downwelling light via its ventral photophores.
When a would-be predator approaches the lure, the shark attaches itself using its suctorial lips and specialized pharynx and neatly excises a chunk of flesh using its bandsaw-like set of lower teeth. This species has been known to travel in schools.
Though rarely encountered because of its oceanic habitat, a handful of documented attacks on humans were apparently caused by cookiecutter sharks. Nevertheless, this diminutive shark is not regarded as highly dangerous. The International Union for Conservation of Nature (IUCN) has listed the cookiecutter shark under Least Concern, as it is widely distributed, has no commercial value, and is not particularly susceptible to fisheries.