Sharks Elasmobranchii

You may have seen the BBC series entitled “Shark”. “Shark” is a three episode series researching many different species of sharks with the aim to change people’s negative opinions towards them; especially since “Jaws” is celebrating its 40th anniversary this year.

Elasmobranchii is the subclass of cartilaginous fish; this includes sharks and rays.

The Elasmobranchii evolved over 400 million years ago – when humans were still in the trees. Today there are 510 different species of shark and 650 species of ray (that we know of). Both sharks and rays have skeletons made of cartilage. Although some scientist believe that this cartilage represents a primitive condition in their evolution (in comparison with other fish and land animals who evolved to have a bone skeleton), it has been recently showed that sharks in fact evolved to have cartilage skeletons in order to be lighter, more flexible and, consequently, faster underwater.

Shark cartilage
(http://www.21food.com)

Rays are essentially flattened sharks with their pectorals having eventually turned into the trademark “wings” that enable them to “fly” through the water.

Both sharks and rays have gills. Sharks have their gills on the side of their head and rays on the underside of their body. Most species have 5 gills, some (although this is rare) have 6 or 7. Some species of shark must keep swimming so that water keeps flowing over their gills and they can breathe. Other species can simply pump water over their gills by opening and closing their mouths, enabling them to sit for hours on the sea bed. (like the Tasselled Wobbegong (Eurcrossorhinus dasypogon))

Tasselled Wobbegong

All sharks and rays have teeth, these vary from tiny teeth used to filter plankton to large teeth used for crushing pray. Sharks never run out of teeth as they are endlessly replaced.

Their skin is something truly incredible as it is covered in tiny modified teeth that reduce drag. This enables the shark to swim faster.  These tiny teeth therefore mean that anything made from shark skin has great grip – such as the grip of a sword. These sword grips (handles) are often made of wood or metal and then (although not done anymore) is covered in shark skin. Shark skin is a hugely durable material in temperate climates, however it isn’t so good in hot climates. Some sword types are made of ray skin instead.

40% of sharks lay eggs with 10% giving birth to live young. About 25% use a mixture of the two methods with the eggs hatching inside the mother and then she gives birth to live young.

If you get attacked by a shark, it is your fault. The BBC team spent two years researching and filming sharks; with 2,646 hours under water, using 1.5 million litres of air, and filming sharks of all sizes across the globe. There was not one single dangerous encounter.

There are 510 species of sharks and 610 species of rays. Over the next few weeks I will be researching some of the different species of sharks and rays that roam our oceans.

Sources:

http://www.bbc.co.uk/programmes/articles/3PQHSqX4NkFpsCysvfdbf5c/what-makes-a-shark
https://en.wikipedia.org/wiki/Elasmobranchii
http://www.telegraph.co.uk/culture/tvandradio/11558501/TV-The-BBC-gets-friendly-with-sharks.html
http://www.iflscience.com/plants-and-animals/no-bones-about-it-sharks-evolved-cartilage-reason
https://en.wikipedia.org/wiki/Hilt