Sharks (Selachii)

2023 Author: Molly Page | [email protected]. Last modified: 2023-11-27 22:49

Sharks belong to the oldest fish living in the seas today. Most modern sharks have an elongated body shape. The exceptions are sharks of the orders of sea angels (Squatiniformes) and pilonos (Pristiophoriformes), which have a sloping body shape compressed in the dorsoventral direction. Sharks differ from all other fish in that their skeleton consists of cartilage, and not of bones, and the gill arches, unlike other fish, are represented by plates that are located in separate gill slits, and are not covered by one gill cover. The number of gill slits varies from 5 to 7 pairs in different sharks. Teethsharks are covered with enamel and can change several times during their life. The skin has small denticles, very similar in structure to the teeth, located on the jaws. The body shape of most sharks is torpedo or fusiform, with the exception of some flat sharks not included in this manual.

Dusky gray shark (Carcharhinus amblyrhynchus)

The size of sharks varies considerably depending on the species. So, the length of small deep-sea spiny sharks does not exceed 25-30 cm, weight - 45-50 g, while the length of the whale shark sometimes exceeds 15 m, the mass reaches several tons. Age most sharks can reach 30-40 years, but usually no more than 15-20 years. The growth rate of sharks is uneven, and the maximum growth occurs in the first 3-7 years. In some species of sharks, the average annual growth during this period ranges from 4 to 12 cm, or (for small and medium species) 10-12% of the body length.

Fins in sharks, like in other fish, are divided into paired - pectoral and abdominal and unpaired - 1st and 2nd dorsal, caudal and anal. Sharks differ from stingrays primarily in that the gill slits are located on the sides of the head, and in stingrays, on the lower surface of the head. The powerful caudal peduncle ends with a large heterocercal caudal fin. Sharks differ from each other in shape and body proportions, size, color and anatomical features.

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The sense of touch is well developed in sharks. Many members of the superorder have a hole in the back of the eye. It comes in various sizes. In addition to their sense of smell, sharks have well-developed eyesight, especially in species that live in the water column. Vision plays an auxiliary role at a distance of up to 10-15 m (to distinguish silhouettes and movement of objects) and the main one at a distance of up to 3 m. Males on the inner side of each pelvic fin have a fleshy protrusion of various shapes, called "mixopterigia" It is used in mating for reproduction. Some shark species are viviparous, others lay eggs, and their shell is horny, usually with filaments at the corners. Some sharks have a blinking membrane on their eyes, which can move upward and close the eye, like our upper eyelids.

The mouth opening in sharks is large, located on the underside of the head (except for the frilled and large-mouthed sharks). The jaws are armed with large teeth. The eyes and nostrils are located on the head. The latter also most often occupy a ventral position. The head of a hammerhead shark has a peculiar shape: lateral outgrowths give it the shape of a hammer or a shovel, on the rostral edges of which are located nostrils. The eyes of sharks of this family lie on the lateral planes of the "hammers". All sharks have a cloaca.

Pelagic fox shark, or small-toothed fox shark (Alopias pelagicus), photo photograph dangerous fish

Pelagic fox shark, or small-toothed fox shark (Alopias pelagicus). Photo by Klaus Stiefel

In the skin of sharks, placoid scales are located (and are constantly formed), which are spines, the shell of which consists of dentin. The top of the scale is covered with a dense layer of enamel. Inside the scale, there is a cavity filled with loose tissue saturated with blood vessels. Scales, like shark teeth, have a wide variety of shapes. All modern sharks lack bones in the skeleton; the internal skeleton is completely cartilaginous. In large individuals, there is a significant calcification of the cartilage, especially the spine. Skullsharks, like other vertebrates, are divided into two sections - cerebral, or neurocranium, and visceral. The three-lobed liver of sharks is large, its weight is about 10%, and in some species of sharks - about 20% of body weight. Shark liver accumulates huge amounts of fat (up to 70% of the mass), as a result of which it plays the role of not only a depot of energy resources, but also a hydrostatic organ that increases the buoyancy of the shark's body, devoid of a swim bladder.

Sharks and other cartilaginous fish have only one circle of blood circulation, and only venous blood enters the heart. Sharks have a two-chambered heart, consisting of an atrium and a ventricle. The main organs of excretion in sharks are the trunk, or mesonephric, kidneys, which lie in the form of elongated bodies along the spine. The main organs of excretion in sharks are the trunk, or mesonephric, kidneys, which lie in the form of elongated bodies along the spine.

By the type of reproduction and development, sharks are divided into three unequal groups: oviparous, ovoviviparous and viviparous. Shark eggs usually have a complex shape and varying length of outgrowths. The number of eggs laid by one female can range from one or two to several dozen.

Not all modern sharks lead a predatory lifestyle. According to the type of feeding, all modern sharks can be divided into four groups: typical benthophages; specialized plankton feeders; active oceanic and neritic predators; sharks with mixed bottom-pelagic nutrition. Typical benthophages include bottom and bottom sharks of the following orders: motley sharks, sea angels, pilonos and many representatives of the order Carcharhiniformes. The group of specialized plankton-feeders is extremely peculiar and small in number. It includes only three species of modern sharks: whale, giant and megapast, or largemouth. Plankton-feeding sharks have almost no natural enemies, but baleen whales and large pelagic rays of the genera Manta and Mobula compete with them in their diet.

Active oceanic and neritic predators include the most progressive sharks of the families of gray sharks and hammerhead sharks of the Carcharhiniformes order, as well as representatives of the Lamniformes order (except for the house shark). Sharks of this group feed on small, medium-sized and large schooling bony fishes (herring, salmon, mackerel, horse mackerel, tuna, alepisaurs, etc.), small cartilaginous fishes and cephalopods, squid. Sharks of great depths and active predators of the water column occupy one of the upper steps of the food pyramid of the World Ocean, and in some cases (for example, sharks of epipelagic or fresh waters) - the upper one. Competitors in the diet of this group of sharks are large pelagic fish (swordfish, tuna, etc.) and toothed whales (sperm whales, dolphins).

Common sand shark (Carcharias taurus), photo photograph predatory fish

Common sand shark (Carcharias taurus). Photo by Richard Ling

Modern sharks are commonin the World Ocean from the ice edge to the equator, from the surface to a depth of more than 2 km. However, in some areas of the ocean, sharks are far from evenly distributed. The overwhelming majority of sharks living today are found within the shelf (about 68% of existing ones); about 10% of species live in the bottom layer of water above the continental slope, and only about 22% of all species live in the open ocean. Separate populations of sharks live in fresh waters (the Tigris, Zambezi, Amazon, Lake Nicaragua, and others). A large number of modern shark species live directly on the bottom. Some shark species in certain areas of the ocean form aggregations that differ in size. In tropical and subtropical latitudes, the highest species diversity of sharks is characteristic of the warm island regions and the tip of South Africa.

Many shark species migrate over fairly long distances. Regular vertical migrations are made by many deep-sea sharks of the Squaliformes order, living at depths of 450 m or more in the daytime, and rising to the surface at night. Ancient relict shark species are characterized by habitat at great depths (more than 450 m), characterized by great stability of conditions, which, apparently, contributed to the preservation of these forms to the present day.

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Many shark species are completely edible, some cannot eat the liver, others are too tough or bitter, but most of the species most commonly caught are good tasting and are highly valued in the world market. Mako, herring and katran sharks, for example, are bought by Italy for up to $ 1,000 per ton (more expensive than tuna). Many shark species that are not in demand in Europe are highly prized on other continents, for example, in Africa - the hammerhead shark, in America - the fox shark.

In general, all sharks with dense meat have high taste. In Chile, for example, sharks account for about 10% of all fish eaten. Sharks are boiled, fried, salted, smoked, etc. Shark fins are highly prized in many countries, especially in Asia. Currently, the demand for shark fins in the eastern countries far exceeds the supply. All fins with a length of at least 15 cm are valued, with the exception of the caudal. Canadians use katran shark meat to make fish sticks. The Japanese prepare a number of national dishes from this shark. From the katran shark in Turkey, they produce balyks for sturgeon. The meat of many shark species is white or slightly pinkish, juicy and pleasing to the eye. However, the taste of the meat of most sharks differs sharply from the taste of other Atlantic fish - it is bitter and sour with an unpleasant specific smell. Shark meat cannot be eaten without special processing.

Spotted wobbegong, or Australian carpet shark (Orectolobus maculatus), photo photograph dangerous fish

Australian carpet shark (Orectolobus maculatus). Photo by Richard Ling

Shark skin is used very widely: if it has small sharp teeth, - as an abrasive material, if it is smooth (in most species) - for various crafts. For the production of feed meal, sharks are very widely used, the meat of which does not have high taste.

Systematics of the Shark superorder:

Order / Order: Carcharhiniformes Compagno, 1977 = Carchariniformes
- Family: Carcharhinidae Jordan et Evermann = Gray Sharks
- Family: Hemigaleidae Hasse = Big-eyed sharks
- Family: Leptochariidae Gray, 1851 = Whiskered Dog Shark
- Family: Proscylliidae Fowler = Striped Cat Sharks
- Family: Pseudotriakidae Gill = False shark
- Family: Scyliorhinidae Gill, 1862 = Cat sharks
- Family: Sphyrnidae Gill = Hammerhead sharks
- Family: Triakidae Gray = Mussel Sharks
Order / Order: Cladoselachiformes =

Family: Cladoselachidae Dean, 1894 = Cladoselachidae
Troop / Order: Eugeneodontida =
Unit / Order: Euselachii =
- Family: Hybodontidae =
- Family: Phoebodontidae =
Order / Order: Heterodontiformes Berg = Mixed-Toothed Sharks

Family: Heterodontidae Gray = Bull, horned sharks
Order / Order: Hexanchiformes de Buen, 1926 = Polygilliformes
- Family: Chlamydoselachidae Garman, 1884 = Frilled sharks
- Family: Hexanchidae Gray = Multigill, or comb-toothed sharks
Order / Order: Lamniformes = Lamniform
- Family: Alopiidae Bonaparte, 1838 = Fox sharks
- Family: Cetorhinidae Gill = Giant sharks
- Family: Lamnidae Müller et Henle, 1838 = Lamn, herring sharks
- Family: Megachasmidae Taylor, Compagno et Struhsaker = Bigmouth Sharks
- Family: Mitsukurinidae Jordan, 1898 = Scapanorhynchids, house sharks
- Family: Odontaspididae Müller et Henle = Sand Sharks
- Family: Pseudocarchariidae Compagno = Sand Sharks
Order / Order: Orectolobiformes Applegate, 1972 = Wobbegong-like
- Family: Brachaeluridae Applegate = Saddle Sharks
- Family: Ginglymostomatidae Gill = Nurse sharks, baleen sharks
- Family: Hemiscylliidae Gill, 1862 = Asian cat sharks
- Family: Orectolobidae Gill = Carpet sharks, wobbegongs
- Family: Parascylliidae Gill = Collar sharks
- Family: Rhincodontidae Müller et Henle = Whale sharks
- Family: Stegostomatidae Gill = Zebra sharks, zebra sharks
Order / Order: Pristiophoriformes = Pilonose

Family: Pristiophoridae Bleeker = Saw-nosed sharks
Troop / Order: Squaliformes Goodrich, 1909 = Squaliformes
- Family: Centrophoridae Bleeker = Short-spiked sharks, or needle sharks
- Family: Dalatiidae Gray = Serpentine sharks, or sleeping sharks
- Family: Echinorhinidae Gill = Star-spiked or plaque-spiked sharks
- Family: Etmopteridae Fowler = Lamp sharks, or glowing sharks
- Family: Oxynotidae Gill = Triangular sharks, centrin
- Family: Somniosidae Jordan = Smallmouth sharks, or upright sharks
- Family: Squalidae Blainville = Katran sharks, or prickly sharks, or upright sharks
Order / Order: Squatiniformes = Squatiniformes

Family: Squatinidae Bonaparte = Squatinidae, flat-bodied sharks, sea angels
Order / Order: Symmoriida =
Troop / Order: Xenacanthida =

Family: Diploselachidae =