Sharks are a group of fishes characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii), and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the suborder Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus. Under this broader definition, the earliest known sharks date from more than 420 million years ago.
Since that time, sharks have diversified into over 400 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (39 ft). Despite its size, the whale shark feeds only on plankton, squid, and small fish by filter feeding. Sharks are found in all seas and are common down to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark that can survive in both seawater and freshwater. They breathe through five to seven gill slits. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They also have several sets of replaceable teeth.
Jonathan Bird's Blue World is an educational television program about the underwater world. The show is hosted by underwater cinematographer Jonathan Bird. This series airs on PBS stations in the US. The program is designed for family viewing, and each segment finds Bird trying to unravel a mystery, witness an animal behavior or explore an underwater environment. The first season consisted of 5 half-hour programs filmed in standard definition, and the second season contained 7 half-hour programs shot in high-definition. The second season won four New England Emmy Awards. The pilot episode from season 1 won a CINE Golden Eagle Award. Season three consists of 9 half-hour programs in HD and will be released August 29, 2011. The program is magazine format with each television episode consisting of 2-3 segments. These segments appear individually on the Blue World website as webisodes.
Episode 1: Blue Shark Adventure, Underwater Cavern, Giants of the Depths
Episode 2: Swimming with Jaws, The Bandana Game, The Shark and the Whale
The Shark is not a friendly fish
That fact it's always proving
It seems this creatures' favorite dish is
Anything that's moving
He'll chew your face off in a flash
Or cheat you if you let him
So never loan him any cash
And be careful when you pet him
Head is pounding in a daze
Bruised wrists and your body aches
If you be mine I'll be your mirror
Glide inside, pull your trigger
Violent mind, violent mind, violent mind
Violent mind, violent mind, violent mind
I know what you wanna do, we're on the line
I know what you wanna do
Got a violent mind
I know where you're going to
Eyes black and wide
I know what you wanna do
Got a violent mind
Hedonistic, narcissistic
Erotic, nihilistic
Pupils wide, gonna slide inside
Gonna blow your mind
Violent mind, violent mind, violent mind
Violent mind, violent mind, violent mind
I know what you wanna do,
We're on the line
I know what you wanna do,
Got a violent mind
I know where you're going to,
Eyes black and wide
I know what you wanna do,
Got a violent mind
Violent mind, violent mind, violent mind
Violent mind, violent mind, violent mind
I know what you wanna do,
We're on the line
I know what you wanna do,
Got a violent mind
I know where you're going to,
Eyes black and wide
I know what you wanna do,
Got a violent mind
I know where you're going to,
Eyes black and wide
I know what you wanna do,
This afternoon
Your back's not so straight
Your eyes aren't too clear
I could kiss you
For remembering my birthday
Find you on the dock
Out of money out of luck
You should thank me
For remembering your name
You could be very easy
Spin the shotglass
Kiss the bottle
Shark in your brain
Spin the shotglass
Kill the bottle
Shark in your brain
'Cause she's warm
This afternoon
Your bite's not so bad
Your bark's not too scary
I could kiss you
For remembering my address
Find you in the dumps
Out of money out of drugs
You should thank me
For offering my mattress
You could be very easy
Spin the shotglass
Kiss the bottle
Shark in your brain
Spin the shotglass
Kill the bottle
Shark in your brain
'Cause she's warm
Spin the shotglass
Shoot the bottle
I find angels over drinks
Called you on the telephone
See if you were home alone
And we sat
We talked
We watched tv
Love the way you looked at me
And I had to hold it in
I had to hold it in
I had to hold it in
You said you were my friend
Woke up to and I never told you
There was a clock radio by my telephone
And I laid with you in bed
And I had to hold your head
And I had to hold it in
I had to hold it in
I had to hold it in
You said you were my friend
I was the one who held your hand
I was the one who was your friend
I was the one who held your hand
I was the one who was your friend
I was the one
I was the one
And I had to hold it in
I had to hold it in
I had to hold it in