FREE ESSAY ON DIFFERENT TYPES OF SHARKS

DIFFERENT TYPES OF SHARKS

INTRODUCTION
Although sharks belong to the class Chondrichtyes, there are many different types. Sharks
arose about 350 million years ago and have remained virtually unchanged for the past 70
million years and still comprise a dominant group. It is thought that sharks almost
certainly evolved from placoderms, a group of primitive jawed fishes. It took a long
series of successful and unsuccessful mutations with fin, jaw positions etc to give us
all the different designs of sharks around today. When asked to draw a shark, most people
would draw a shape along the lines of the whaler shark family, tigers or a mackeral shark
such as a porbeagle. However many people do not realize the sheer diversity in the shape
of sharks, or that rays are really sharks. 
Seldom does such an animal inspire such a variety of emotions reflecting a mixture of
fascination, awe and fear. Sharks have occasionally exacted a terrible price from humans
who have trespassed on their territory. No better understood than the ocean that they
inhabit, these creatures should be regarded in the same way as lions, tigers, and bears:
as dangerous, predatory but nonetheless magnificent animals.
Different Types of Sharks
Living sharks are divided into eight major orders, each easily recognizable by certain
external characteristics. Each order contains one or more smaller groups, or families. In
all there are 30 families of sharks and they contain the 350 or more different kinds or
species of sharks. 
The eight major orders of sharks include the Squantiformes, Pristiophormes, Squaliformes,
Hexanchiformes, Carcharhiniformes, Lamniformes, Orectolobiformes, and the
Heterodotiformes. The orders have distinguishing characteristics that fit in each. 
The Squantiformes normally have flat bodies that are ray-like with mottled dorsal
surfaces. These sharks have a short terminal mouth, which is armed with small impaling
teeth. They also have a caudal fin, which has a lower lobe that is longer than the upper
lobe. Their pectoral fins extend forward over the ventrally directed gills. 
The Pristiophormes have more of an elongated snout, which is saw-like and edged with
slender, needle-sharp lateral teeth. They have two dorsal fins and no anal fin. They use
short transverse mouths and small cuspidate holding teeth in both jaws.
Squaliformes have no anal fin as well, but their snout is not elongated, but is somewhat
long. Many have powerful cutting teeth in both jaws. In some species these razor sharp
teeth are in the lower jaw only and the upper teeth serve to hold the food. 
Hexanchiformes have six or seven gill slits. They are sharks with a single spineless
dorsal fin, and an anal fin. 
The typical Carcharhiniforme has an elongated snout, a long mouth that reaches behind the
eyes, an anal fin and two spineless dorsal fins. The eyes have movable, nictitating lower
eyelids worked by unique muscles. Teeth vary from small and cuspidate or flattened to
large and bladelike. Carcharhiniformes have no enlarged rear crushing teeth. Along with
this they have a spiral scroll intestinal valve.
A Lamniforme shark has an elongated snout. Most have long mouths that reach behind the
eyes, an anal fin and two spineless dorsal fins. They also have a ring intestinal valve.
The Orectolobiformes have pig-like snouts and short mouths that in most species are
connected to the nostrils by grooves. There is an anal fin but no fin spines on the two
dorsal fins. They have uniquely formed barbells at the inside edges of the nostrils.
Heterodotiformes are the only living shark that combines fin spines on their two dorsal
fins and anal fin. They only have five-gill slits.
In each order there are specific types of sharks. Each shark belongs to a family with
different species. The Angel shark (Squantiforme) is just one of the many. It has a
single family of about thirteen species. They are all ovoviviparous livebearers and most
do not exceed 1.5 meters. Saw sharks (Pristiophoriformes) are harmless bottom sharks.
They are also a single family but with five species. They are also ovoviviparous
livebearers. Four sharks that belong to the order Sqauliforme are the Bramble, Dogfish,
and Rough sharks. They have three families with eighty-two species. They too, are
ovoviviparous livebearers. They have more cylindrical bodies. Frilled sharks, Six, and 
Seven gill sharks (Hexanchiformes) have two families and five species. Once again they
are also ovoviviparous livebearers. Usually, these guys are found in deep waters. The
Catsharks, Finback Catshark, False Catshark, Barbelled Houndshark, Weasel, Houndshark,
Hammerhead, and Requiem sharks (Carcharhiniformes) have one hundred and ninety-seven
known species. Most of these sharks are known to be dangerous. They are both oviparous
and ovoviviparous livebearers. This is not the type of shark you would like to have grace
you presence. From the order of Landformes is the Sand, Basking, Goblin, Crocodile,
Megamouth, Thresher, and Mackerel sharks. They come complete with seven families and
fifteen or sixteen species. All of them are ovoviviparous livebearers. These sharks are
found in all seas except Arctic and Antarctic. The last group of sharks would be the
Collared Carpet sharks, Blind, Wobbegongs, Zebra, Longtailed Carpet Sharks, Whale, and
Nurse sharks. They all belong to the order Orectolobiformes and have seven families and
thirty-three species. These sharks prefer the warmer water and are both ovoviviparous and
oviparous livebearers. 
Obviously these sharks come in many different sizes and some are more dangerous than
others. At least eighteen species in four families and nine genera have been implicated
in attacks on humans. Obviously a small shark such as the Pygmy is harmless, but they
still must be treated as a predator especially the bigger ones. The smallest of all
sharks is the Pygmy Ribbontail Catshark, which is about 0.24 meters. Next in line from
smallest to largest would be the Port Jackson Shark, which is about 1.65 meters. After
them would be the Ornate Wobbegong (2.88m) and then the Bull 
shark (3.4m). The average sizes go drastically up from there to the Great White shark,
which is incredibly larger, its about 6.4 meters. The two greatest sizes are the Basking
shark (7.8m) and the Whale shark (13.7m). These sharks listed here are definitely not all
the sharks in the world, they were just meant to give an average range of size for all
sharks. Some of the most dangerous sharks range from about 2 to 8 meters. The Hammerhead,
Great White, Tiger, Blue, and the Bull shark name a few.
There are many types of sharks lurking around in today's ocean. In every one is unique in
its own way. Some are different by size, shape, eating habits, or even the way they
breed. Although with all these differences they are all very similar and that is why the
shark is one of the most amazing creatures of our time. 
Summary
Although sharks belong to the class Chondrichtyes, there are many different types. Sharks
are divided into 8 major orders. Each order contains 1 or more smaller group. There are
350 or more different kinds of species of sharks. The 8 orders are named the
Squantiformes, Pristiophormes, Squaliformes, Hexanchiformes, Carcharhiniformes,
Lamniformes, Orectolobiformes, and the Heterodotiformes. These orders group sharks
according to certain distinguishing characteristics. The Angel shark, Saw shark, Frilled
shark, Hammerhead shark, Sand shark, Wobbegongs, and more all belong to a specific order
due to their characteristics. Each one of these sharks come in different shapes and
sizes. Some are more dangerous than others. The more dangerous sharks range from about 2
to 8 meters. It is obvious that sharks are one of the most amazing creatures of our time.

Bibliography 
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