Fast, cruel and scary: these are the descriptions most people would give to sharks, right? Especially because all these characteristics are real. However, these underwater beings are much more than that: they are essential to the marine ecosystem and maintain the perfect balance of the oceans.

Also, there are some facts about sharks that a lot of people are unaware of. These are fascinating and surprising aspects that biologists and environmentalists would like everyone to know in order to avoid the indiscriminate killing that has been going on. Check it out below.

Glow in the depths

Image Source: Reproduction / National Geographic

Did you know that there is a small species of shark popularly called a lantern shark? Etmopterus splendidus has this nickname because it is able to shine to camouflage itself on the ocean floor, emitting the same amount of light that comes from top to bottom. That way, they don't cast a shadow and are virtually invisible, making it harder for predators to find them.

Reproductive independence

Females of some shark species can reproduce without the need for a male. Evolution? In fact, this happens to these females due to the phenomenon of parthenogenesis with embryos created from the female gamete, practically cloning themselves.

This has already been found in captive-bred sharks, and in 2001 a female hammerhead shark gave birth at Henry Doorly Zoo in Nebraska without mating with a male, catching researchers by surprise.

Caries protection

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Did you know that shark teeth are already naturally protected? This is because they are covered with fluorine, which leaves them caries free. A study published in 2012 revealed that shark tooth enamel is a chemical called fluoroapatite, which is resistant to the acid produced by bacteria. This, combined with the fact that most sharks replace their teeth throughout their lives, means that they have excellent dental health.

Thick skin

As always, nature is in charge of creating what is best for each species. This way, a female shark's skin is much thicker than a male's because they bite the females during mating. The finding was made by David Shiffman, a researcher and doctoral student at the University of Miami.

Slow but smart

Image Source: Reproduction / National Geographic

The greenest shark, the slowest moving fish ever recorded, has been found with reindeer, polar bears and fast seals in its stomach, researcher David Shiffman told LiveScience. This shark is believed to hunt seals while they are sleeping in the water to prevent polar bear attacks.

* Posted on 8/8/2013