Have you ever wondered if the shark is a mammal? For those who don’t know, the shark is an animal that lives in the aquatic environment and is widely found in the region of the Brazilian coast.
They are considered predatory, voracious and super important animals in the dynamic balance of the ocean food chain. However, many species of shark are threatened with extinction due to predatory hunting that humans practice.
The shark belongs to the group of craniata , that is, animals that have the skull protecting the brain. The craniatas include fish, amphibians, reptiles, birds and mammals. This animal is also classified as a vertebrate, because in addition to the skull, they have vertebrae, which are part of their cartilaginous endo-skeleton (internal skeleton).
Among the craniatas there are representatives adapted to the aquatic, terrestrial and aerial environments. The size of the animals in this group ranges from very small, like some fish of about 0.1 gram, to very large animals, such as whales, which reach 170 tons.
The craniata skin is made up of two layers: the outermost epidermis and the innermost dermis . The epidermis is always multi-stratified, that is, formed by several layers of cells, while that of the other animals is always uni-stratified. The dermis is a tissue rich in blood vessels and sensory structures.
Is a shark a mammal or a fish?
The shark is a type of fish and is not a mammal . This animal belongs to the class of chondricks ( chondri = cartilage; ictio = fish). Chondrites have jaws and fins in pairs.
Shark is a species of fish that has predatory habits (Photo: depositphotos)
Perhaps the greatest of all the innovations that arose during the evolutionary history of vertebrates was the development of the jaws, which enabled primitive fish to efficiently extract large pieces of algae and larger animals. This favored greater opportunities for food sources.
The active predatory habit of this fish came associated with a series of changes in the body of this animal, making it a good swimmer, able to move quickly and agility in liquid, thus capturing its prey efficiently. In addition, a series of fins developed, increasing the body’s propulsion capacity.
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How is the skeleton?
The shark’s internal skeleton (endo-skeleton), as well as its skull and other vertebrae, are formed by cartilage . The cartilaginous skeleton gives the animal greater mobility. Sharks represent the largest group of chondrites along with rays (or stingrays), forming about 760 species.
Shark has scales?
Shark scales differ from the scales of bony fish. In these, the scales are of dermal origin, while in the sharks they are of dermal epidermal origin , with a structure similar to the tooth.
Each of them is formed by a spine facing the posterior region of the body and a basal plate located in the dermis. The shape and arrangement of the scales on the body reduces the turbulence of the water around the animal, increasing the efficiency of the swim.
This animal’s mouth and feeding
The shark has an extension of the anterior region of the head and the mouth is transversal, being positioned ventrally. Despite this ventral position of the mouth, these animals are able to bite and pull large pieces from the body of the prey, as their mandibular arch is loosely connected to the skull, making it possible to move the jaws forward.
In addition, their teeth are pointed and occur in rows that are gradually moved to the front of the mouth as the front teeth are lost.
In general, sharks are active carnivores, like the white shark, which reaches 6 meters in length and is a predator of marine mammals. However, there are species that feed on plankton, such as the whale shark, the largest known species of fish, reaching up to 20 meters in length.
See also: Whale shark: curiosities, food and characteristics
Shark’s sensory organs
Chemoreception and mechanoreception are sensory mechanisms that sharks mainly use to perceive the presence of prey at great distances. Once close to them, these animals start to use their vision.
Sharks are able to detect their prey by means of electroreceptors, which are called Lorenzini ampoules and are located on the head. They are pores and tubes filled with mucus, which communicate sensory cells with water.
These cells are capable of detecting the weak electrical current generated by the prey’s muscular activity. The ampoules are sensitive to temperature, salinity and water pressure, with a special ability to detect electric fields generated by other animals.
Sharks have a very developed sense of smell , perceiving the odor by chemoreception from the cells located in their nostrils. Another important sense for the orientation of these animals is their ability to perceive water vibrations .
This is only possible thanks to the presence of structures located along the lateral line of the sharks. The lateral line runs along both sides of the fish’s body and is formed by several superficial pores and tubes. The pores and tubes communicate with water and special cells. These cells pick up vibrations in the water and take them to nerve cells.
The shark and the density
Sharks are efficient swimmers, although there are some rare types of sharks that live on the seabed perched on sand or in burrows. In general, active swimming sharks have high levels of oil in the liver , which reduces the density of these animals in relation to the liquid medium, acting on the regulation of their buoyancy.
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As for reproduction, sharks are animals of separate sexes, with sexual dimorphism. The male differs externally from the female mainly due to the presence of the copulatory organ, the clasper. The clasper corresponds to a modification of the pelvic fins. Fertilization is always internal and development is direct. There are oviparous, ovoviviparous and viviparous species.