Sharks play an essential rol in the health of our oceans

General info

Sharks, rays and skates belong to the cartilaginous fish (Elasmobranchii), with a skeleton consisting of cartilage. Today, the approximately 600 living species of this class are just a reflection of this group of animals that, 250 million years ago, played a dominant role in the world of the fish.

Almost all cartilaginous fish have a long, protuding snout. The gill slits of sharks and rays are clearly visible: sharks have five to seven slits, rays always have five.

Their rigid fins are covered with skin, the tail-fins are asymmetrical. Sharks and rays do not have scales but ‘dermal teeth’, called denticles, that in rays have developed into dermal ‘thorns’.

Most sharks have rows of teeth in their jaws. Missing teeth can be replaced: the row behind the front teeth moves forward. Some species have oblique, serrated teeth to saw through flesh, others have pointed-needle like teeth. In planton-eating species like the basking sharks, the teeth are greatly reduced and have almost disappeared.

Most ray species have thick, plate-like, arranged like roofing tiles. Very suitable to crush mollusks!

Unlike most bony fish, elasmobranchii do not have a swim bladder, but regulate their buoyancy through their oil-filled liver.

Both sharks and rays mate: the eggs are fertilized inside the body. Most young are born alive, but nearly 40% of the sharks and rays deposit their eggs, that are covered with an egg-case, consisting of keratin, on algae and stones.  Depending on the species and eggcase form, the eggs can be attached to algae with long, curly tendrils or left on the seafloor. The egg cases of rays have points.





The largest shark is the whaleshark, that can be 15 meters long, the smallest is small catshark, only 20 cm long.
The largest rays is the giant manta ray with a width of six metres. The smallest ray is probably a fresh-water ray, only measuring 25 cm.




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