Sharks (Meaning and Explanation)

We explain what sharks are, what their diet, habitat, reproduction and other characteristics are like. Also, how they sleep.

What are sharks?

The sharks are a set of cartilaginous fish (that is, without a bone skeleton) popularly known as sharks or sharks and scientifically as selachymorphs either selacimorphs (that is, belonging to the superorder Selachimorph). It is one of the most popular marine animals and feared by humanity, due to its role as a ferocious marine predator.

Sharks make up a very diverse group of animals, which includes large fish and other small ones, in fresh waters or mostly in salt waters, present in practically all geographies of the world.

emerged evolutionarily at the same time as rays and chimeras with whom they share the class Chondrichthyes, 400 million years ago in the Devonian period. Since then they have evolved and changed to give rise to the current 360 species of modern sharks, about 100 million years ago.

Despite their reputation as ferocious animals, Many species of sharks are currently in danger of extinction due to selective hunting by humans. They are caught for sport, or as a source of fins for certain gastronomic dishes, and in the past their rough skin was used as sandpaper.

Shark characteristics

In general, sharks are characterized by the following:

They commonly occupy the role of predators in their various habitats.
are usually torpedo shaped with a powerful tail at the end and a set of three major fins: dorsal (on the animal's back), and two pectorals (on the animal's chest). In addition, it has three other smaller fins: pelvic, anal and a second dorsal fin.
Their bodies are composed of cartilage, except for their powerful jaws full of serrated triangular teeth. The mouth is under the snout, in the shape of an arch and semi-open at all times, and the eyes are one on each side of the skull.
can be huge like the whale shark (18 meters long) or small like the pygmy shark (which fits in a human hand).
breathe through five to seven pairs of gills located on the sides of the head. To do this they must be in continuous movement, so that the water penetrates through their mouths. Likewise, lacking a swim bladder, they must swim constantly or sink to the bottom of the seas.
Their skin is usually rough strong, made up of scales and designed to silence the animal's movements, reducing friction with the water.
The longevity of sharks does not exceed 30 years in most species, although a few can reach a hundred, thanks to the shark's formidable immune system, which is the subject of study by scientists.

Types of sharks

shark heteroodontiform types Heterodontus francisci — Heterodontiformes are accustomed to nocturnal life and reef life.

Within the diversity of sharks there are various orders, which group together species with similar characteristics. These are eight different orders, which are:

Hexanchiform In this order there are six living species grouped into three families, characterized by having six gills, a single dorsal fin and lacking a third eyelid. This is the most primitive order of existing sharks, such as the eel shark (Chlamydoselachus anguineus) or the cow shark (Notorynchus cepedianus).
Squaliformes In this order there are 125 living species, in seven different families, which also lack a third eyelid and also an anal fin, but have two dorsal fins, some of which can be poisonous. The pygmy shark belongs to this order (Euprotomicrus bispinatus) and the sea pig (Oxynotus centrina).
Pristiophoriformes There are eight species of them in two different genera, equipped with six gills and an elongated, toothed snout that resembles a saw, with which they remove the ocean floor in search of their prey. The most representative of the order is the sawshark (Pilotrema warreni).
Squatiniformes Encompassing twenty-two different species in the same genus, they are flattened sharks, adapted to roaming the seabed, detecting their prey buried in the sand there. A good example of this is the angel shark (Squatina dumeril).
Heterodontiformes In this case there are nine species with a short snout, five gills and spines inside their dorsal fins, as they are used to, like the horned suño (Heterodontus francisci) to nightlife and reefs.
Orectolobiformes Composed of 33 species in seven different families, they lack an anal fin and have various types of whiskers connected to their olfactory organs (nostrils). Examples of this order are the dogfish (Ginglymostoma cirratum) and the immense whale shark (Rhincodon typus).
Carcharhiniformes Composed of 197 species in eight different families, it is the most complex group of sharks, they have five gills and wide, rounded snouts, sometimes with particular shapes, like the hammerhead shark (Sphyrna mokarran), the bull shark (Carcharhinus leucas) or the blue shark (Prionace glauca).
Lamniformes In this order there are 16 species grouped into seven families, and they are the classic movie sharks, those that have large teeth growing under the eyes, five gills and the complete set of fins. Here we find the great white shark (Carcharodon carcharias), to the mako shark (Isurus oxyrinchus) or the basking shark (Cetorhinus maximus).

Shark feeding

sharks feeding predator — Sharks feed on a wide variety of marine species.

Sharks are mostly predators, so Their diet is generally carnivorous covering a very wide range of marine species: fish, marine mammals, mollusks, marine arthropods or even other sharks. It all depends on the size and habitat of the shark. They may also resort to ingesting carrion, depending on the case.

However, three species of sharks (whale shark, basking shark and largemouth shark) instead feed through a water filtering mechanism, ingesting phytoplankton, nekton, algae and krill, as well as larvae, small crustaceans, squid or even small fish. such as anchovy, sardine or certain types of tuna, thanks to specialized structures of their own gills.

Shark habitat

The sharks exist practically throughout the world since their geographical ranges are difficult to determine. The species they move over great distances according to their feeding habits or their mating seasons, and can alternate between deep and surface waters, although many species have very well-defined niches.

Shark reproduction

sharks reproduction — Depending on the species, sharks can have anywhere from two babies to almost a hundred.

The sharks reproduce through internal fertilization of the eggs laid by the female that is, they are fertilized by the male inside the female's body and not outside, as in other species of fish. Copulation occurs either by the male curling around the female, or by placing themselves parallel, in the largest and most rigid species.

How do sharks sleep?

Since sharks lack a swim bladder, they cannot remain still without sinking to the bottom, and if the water stopped entering through their mouths towards their gills, they would drown.

Therefore, their sleep periods are brief and on the move during which only a portion of your nervous system rests. Thus, they rest in full movement, immersed in a kind of active torpor.

Shark attacks

Contrary to what cinema and popular stories suggest, the species of sharks that represent a danger to humans are very few and are generally reduced from the almost 400 existing, to the white shark, the tiger shark, the blue shark, the hammerhead shark and the sarda shark.

In places like Australia, New Zealand or South Africa, there is a possible warning of shark attacks for bathers or surfers. Surveillance towers, protection networks and other mechanisms are often used to protect people.

However, humans are not part of the sharks' diet. Most attacks occur by mistake since the shark mistakes a surfer for a porpoise or some other type of marine mammal, or as a way to “test” what this curious creature that has been found is about.

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