Information about the anatomy and sensory system of sharks
Sharks are a group of fish characterized by a cartilaginous skeleton.
They have five to seven gills on the side of the head.
The smalles shark today is about 30 cm long; the longest 12-14 m long.
The biggest shark that has ever lived was the C. Megalodon, that could have a length of up to 18 m and was an active predator. It went exticnt around 1.6 million years ago.
The sexes of sharks are distinguishable from birth on, now that they have exterior sexual characteristics.
Source: http://en.wikipedia.org/wiki/File:Megalodon_scale1.png
Figure: Comparison of sizes. The green shark is the present Great White Shark
Teeth:
Shark teeth are embedded in the gums rather than directly
affixed to the jaw.
They are replaced throughout a shark's lifetime. Multiple rows
of replacement teeth grow in a groove on the inside of
the jaw. Some sharks lose 30'000 or more teeth in
their lifetime.
Tooth shape depends on what the shark eats.
Jaw:
The jaws of sharks are not attached to the cranium, this is
why they are flexible.
Fins:
Fin skeletons are elongated and supported with soft, unsegmented rays called ceratotrichia; filaments of elastic protein resemling the horny keratin in hair and feathers.Most sharks have 8 fins, but the number can vary from species to species. The stiff fins of a shark are the reason it can't swim backwards, as opposed to other fish.
Skin:
Unlike bony fish, sharks have a complex dermal structure (denticles) made up of flexible collagenous fibers arranged as a helical network.
These "dermal teeth" give them hydrodynamic advantages as they reduce turbulence when swimming. Also the coloration is adapted for being a good predator. Their back is dark so that they can hardly be seen from above and their belly is whitish so that they won't stand off the light background from below.
Buoyancy:
Unlike bony fish, sharks do not have a gas-filled swim bladder for buoyancy. They do however have a large oil-filled liver and their cartilage is about half the weight of bones. Nevertheless, sharks - if not swimming - will sink to the ground.
Respiration:
Sharks, like other fish, extract oxygen from the seawater as it passes over their gills.
Shark gill slits are not covered.
While the shark is moving, water passes through the mouth and over the gills, which is called "ram ventilation".
While at rest, most sharks actively pump water over their gills to ensure constant supply with oxygen.
Some sharks have lost the ability to pump water through their gills and must swim without rest, otherwise they would asphyxiate.
Thermoregulation:
Most sharks are poliothermic, which means that their internal body temperature matches the one of the environment.
Some sharks - as the Great White - are homeothermic and maintain a higher body temperature than their surrounding water.
Osmoregulation:
The blood of sharks is isotonic to their marine environment; they have an osmotic balance with the seawater. It is this adaptation that prevents most sharks from living in fresh water. They can however influence the composition of their blood. In water with low salt content, they can increase the volume of their blood by increasing its water content.
The senses of sharks:
Smell:
Sharks have very good smell which allows them to detect as little as one ppm (part per million) of blood in seawater.
They have the ability to determine the direction of a given scent.
Sight:
Sharks have eyes similar to most vertebrates, but their eyes are well adapted to the marine environment with the help of a tissue called tapetum lucidum. They can contrast and dialte their pupils.
Sharks have eyelides, but they don't blink because the water cleans the eyes. A shark's field of vision can swap between monocular and stereoscopic at any time. They have good night visions, but they are colorblind.
Hearing:
Sharks are thought to have good hearing; they can hear their prey miles away. Sharks are sensitive to noises of exactly the low-wavelength sounds that moving muscles make.
Source: http://en.wikipedia.org/w/index.php?title=File:Parts_of_a_shark.svg&page=1
Figure: Anatomy of a Shark
Electroreception:
The ampullae of Lorenzini are electroreceptor organs that number in the hundreds to thousands. Sharks use them to detect the electromagnetic fields that all living things produce, which helps them to find prey.
The shark has the greatest electrical sensitivity of any animal. This sense allows sharks to even sense fish that are buried in sand.
Ocean currents moving in the magnetic field of the Earth also generate electric fields that sharks can use for orientation and navigation.
Lateral line:
It is used to detect motion or vibration in the water. Sharks can sense frequencies in the range of 25 to 50 Hz.
Source: http://en.wikipedia.org/w/index.php?title=File:Electroreceptors_in_a_sharks_head.svg&page=1
Figure: The electroreceptors as part of the Ampullae of Lorenzini
Source: http://www.sharkproject.org/haiothek/index.php?site=anatomie_8.
Figure: Male: claspersM Female: cloaca.
Copyright December 2014; Olivia Lucie Meier, Sharkworld.