Shark: characteristics, species and curiosities

shark is a popular name used to name a type of fish of the group of chondrites, that is, those that have a skeleton predominantly formed by cartilage. Sharks are well known, mainly, as large predators, but this characteristic cannot be applied to all representatives of this group of animals.

Read too:Differences between bony and cartilaginous fish

→ Features

Sharks are animals that are part of the same group of stingrays and chimeras, and, as they are fish, they have some very striking characteristics of this group of animals. Below are some of these characteristics observed in sharks:

Branchial respiration: like all fish, sharks are animals that breathe for gills, that is, they use these structures to ensure the removal of oxygen from the water.
Hydrodynamic body: sharks have a body that helps their movement in the aquatic environment, helping them to break the resistance of the water.
Placoid scales: make sharks have a surface that resembles sandpaper. These scales ensure more efficient swimming and have a tooth-like structure.

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Fins: assist in movement in the aquatic environment. Strong movements of the trunk and tail fin ensure the animal's movement. The pectoral and pelvic fins help with maneuvers, while the dorsal fins help as stabilizers.
Absence of swim bladder: sharks do not have a swim bladder, which is a structure related to buoyancy. To resolve this issue, sharks have a large liver, which contributes about 25% of their fat-filled body mass. This causes the animal's density to decrease.
Electric field capture structures: animals, when presenting muscle contraction, cause electrical signals to be emitted. Sharks are able to pick up these electrical fields and are therefore able to locate prey even if it is hidden.
Claspers: structures found in male sharks that act as organs responsible for the deposition of the gamete inside the female's body. Due to this characteristic, we say that the fertilization of the shark is internal.
Cloaca: sharks have a cloaca, that is, they have a chamber into which the reproductive, excretory and digestive systems flow.
They can be oviparous, ovoviviparous or viviparous: there are sharks capable of laying eggs (oviparous), sharks that retain eggs in their oviduct (ovoviviparous) and sharks that are able to ensure the development of your offspring inside the uterus (viviparous).

Note the opening of the gills laterally to the animal's body.

→ What do sharks eat?

Many people know sharks as great. predators that feed on large animals such as seals. Some sharks actually exhibit this type of behavior, this being the case of the white shark, a species that feeds in addition to seals, in fish and even sea turtles.

It is worth noting, however, that not all sharks have this behavior. This is the case, for example, with the Whale shark, which is classified as strainer. This animal feeds mainly onplankton.

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→ Species

As said, sharks are not just a single species. Several species can therefore receive this designation. Next we'll talk about some of the most notorious sharks found in the world.

White shark (Carcharodon carcharias): occurs in most of the seas and oceans, being observed, even less frequently, even in Brazil. It can reach about six meters in length and live for about 70 years. It is a great predator of the seas and feeds on the most varied animals, including other fish, turtles, seals and penguins. It is a very hunted species for the removal of its fins, which are used to make soups.

The white shark became famous after the movie shark, by Steven Spielberg.

Whale shark (rhincodon typus): species that has a robust body and flat head, which is the largest existing shark. Its color is black, with lighter spots all over the body. This species feeds through filtration, ingesting some small fish and plankton present in the water. For this species, there are records of individuals with 20 meters in length and 35 tons.

The whale shark is the largest shark in the world.

Hammer shark: the name of hammerhead shark is given to species of the genus Sphyrna. A striking feature of this type of shark is the presence of a flat head typical of the group. The head, despite appearing inefficient, helps these animals in the swimming process and in visualizing their prey. Hammer shark species vary in size. the species Sphyrna zygaena, for example, it can reach five meters in length and weigh about 400 kg.

The hammerhead shark has a characteristic head.

→ Curiosities

Fun Facts About Sharks

Despite being animals that reproduce sexually, there is a report of a female hammerhead shark that reproduced alone, without the need for a male, in a zoo in the United States. This individual reproduced asexually by parthenogenesis.

Sharks can have gestation with more than one offspring, and in some cases the death of one offspring by another still inside the uterus is observed. When one offspring devours the other still inside the mother's body, we say that there was intrauterine cannibalism.

Shark attacks are rare around the world. A survey conducted in the United States showed that more people died between 2001 and 2013 from attacks by dogs (364 deaths) than from shark attacks (11 deaths).

Sharks have a very keen sense of smell. Some sharks are able to respond to substances in concentrations less than one part per 10 billion.

The white shark, when it feeds on mammals such as seals, kills these animals by bleeding. In these situations, what is observed is that the shark holds the seal with its jaw until the prey stops bleeding, then it removes large pieces of the animal. In the case of sea lions, which are stronger prey, sharks trap and release the animal several times until it dies from hemorrhage.

The white shark is the best known and most feared shark. One of the reasons for the "bad reputation" of white sharks is the movie shark, directed by Steven Spielberg and released in 1975. The work, which shows a great white shark attacking tourists on a beach, was a great success, winning the Oscar for best original soundtrack, best sound mixing and best editing.

By Ma. Vanessa Sardinha dos Santos

Would you like to reference this text in a school or academic work? Look:

SANTOS, Vanessa Sardinha dos. "Shark"; Brazil School. Available in: https://brasilescola.uol.com.br/animais/tubarao.htm. Accessed on June 27, 2021.