Not just Shark
Pictures: Elasmodiver contains photos of sharks, skates, rays, and
chimaera's from around the world. Elasmodiver began as a simple web
based shark field guide to help divers find the best places to
encounter the different species of sharks and rays that live in
shallow water but it has slowly evolved into a much larger project
containing information on all aspects of shark diving and shark
There are now
more than 5000 shark pictures and sections on shark evolution,
biology, and conservation. There is a large library of reviewed
shark books, a constantly updated shark taxonomy page, a monster
list of shark links, and deeper in the site there are numerous
articles and stories about shark encounters. Elasmodiver is now so
difficult to check for updates, that new information and pictures
are listed on an Elasmodiver Updates Page that can be accessed here:
don't have time to read all the information contained on Elasmodiver, here
are some quick facts about sharks and rays. Great for school projects.
How are sharks and rays different from other
and rays do not have true bones like other fishes. They have
cartilage instead which is lighter and much more elastic and allows them
to bend in very tight circles.
not have swim bladders. A swim bladder is a gas filled sack inside
the body of bony fishes that allows them to stay still without sinking.
Sharks compensate by having a very big liver that is filled with oil.
Even so, sharks sink unless they keep swimming forward. The exception is the
SandtigerShark which swallows air to make itself more
upper jaw is not fused to its skull like most animals. When a shark
bites a large object, it is able to move its upper and lower jaw forward in
order to take a bigger bite.
other fishes, sharks are able to replace their teeth
constantly. New teeth grow from the inner surface of the jaw and rotate
forward when the old teeth get worn out or lost during feeding.
and rays do not reproduce like other fishes. Most fish release clouds
of sperm and eggs into the water column where they mix together. The
fertilized eggs then float around until the fish larvae hatch and form
schools of tiny fish. Male sharks have two organs called claspers
attached to their anal fins. They insert one of these into the female
shark's cloaca (the entrance to the uterus) to transfer sperm (just
like in mammals). Some sharks and rays incubate the eggs in their uteruses
until the baby sharks are ready to be born. Other sharks and rays (i.e.
skates) lay eggs and attach them to the reef.
have between 5 and 7 gill slits on each side of their body in front
of their pectoral fins. Bony fishes only have one pair. Having many exposed
gill slits probably helps transfer more oxygen into their blood faster which
allows them to swim very fast when they need to.
shark's skin is covered in small denticles instead of scales.
Denticles are a lot like teeth. They have dentine in the centre
and enamel on the surface. This makes shark's skin very tough and
abrasive like sandpaper. The shape and position of some shark's denticles
also helps reduce friction so that they can slip through the water
have an extra sense that is able to detect tiny electric fields.
They can use this to find food that is buried or to search for animals to eat
in the dark or in turbid water.
and rays make up the sub-class of fishes called elasmobranches. This
sub-class is part of a class of cartilaginous fishes called
Chondrichthyes which also
includes chimaeras (ratfishes).
and rays are usually very wary of people and most sharks will swim
away long before you see them.
nearly 500 species of sharks but only a few are likely to be
involved in an attack. Some of the more dangerous sharks include the Great
White Shark, the Tiger Shark, and the Bull Shark.
not normally treat humans as food. If they did, it would be very easy for
them to eat all of the people who play in the water at the beach because
they are much better swimmers than we are. Most scientists agree that
attacks are usually the result of mistaken identity or the sharks
feeling threatened because they are cornered. In places like California
where there are a lot of White Shark attacks on surfers, scientists
believe that the sharks think that the surfers look like seals or sea lions.
are completely harmless but stingrays have one or more barbs on their
tails that they use to defend themselves. If they are caught by fishermen,
cornered, or trodden on in the sand, they sometimes stab their barb into
whoever is threatening them. The barb has a painful venom on it but
stingray wounds are rarely fatal unless there is no medical attention
available. The Amazon natives fear the freshwater stingrays that live in the
river because it is very difficult for them to treat the wounds.
way to avoid stingrays is to shuffle your feet when you are walking
in water where stingrays live.
and rays have a very varied diet. They are carnivores which means
that they eat animals rather than plants and algae. Some sharks commonly eat
bony fishes, crustaceans (crabs, lobsters, and other animals
with an external skeleton), mollusks (snails, sea slugs, octopus and
squids), and different types of worms.
diet is often determined by its habitat. For example, sharks that live out
at sea (pelagic sharks) are more likely to eat fish and squid
because that is all that is available.
sharks change their diet as they get older. The Great White Shark
mainly eats fish when it is young but once it reaches maturity it consumes
more marine mammals like seals and sea lions.
sharks prefer live food but they will also consume carrion
(dead fish and other animals) that they find on the sea floor.
filter feeding whales, there are a few sharks that live by filtering
plankton from the water. The filter feeding sharks may consume
phytoplankton (microscopic plants and algae) while hunting for more
nourishing zooplankton (tiny animals and larvae that drifts around on
the currents). Ironically, the Whale Shark which is the largest fish
in the sea, lives on plankton which is one of the smallest animals. So does
the second largest fish; the Basking Shark. Although these sharks
have huge mouths, their throats are tiny and they are unable to eat anything
larger than a grapefruit. Their teeth which are no longer needed for
feeding, have become very small.
largest ray (the Manta Ray) is also a plankton feeder. It has a
flexible projection on each side of its mouth called cephalic lobes
that it uses to funnel plankton towards its mouth.
rays eat small fishes and benthic invertebrates; crabs, snails,
and worms etc. that live on or under the sand.
its possible to tell what type of food a shark eats by the shape of its
teeth. Sharks that catch fast swimming fishes tend to have very pointed
teeth that help them grasp the fish. Sharks that eat hard shelled
animals have flattened teeth that form a plate to help them crush the
creature's shell like a nutcracker.
Sharks have a reputation for eating anything. They have been found with
all sorts of strange things in their stomachs from clothes to license
plates. Tiger Sharks have very sharp serrated teeth that are strong
enough to bite through the shells of marine turtles.
have been evolving for about 400 million years. Some of the early
sharks looked very different from the ones we see now.
have been around much longer than rays. Paleontologists believe that rays
evolved from flattened sharks about 200 million years ago. The first
rays were probably guitarfish. Over time, they adapted to life on the sand
by becoming more and more flattened.
Fossils are formed when minerals slowly replace buried bones and
tissues. The best fossils come from bones because they last a long time
before they disintegrate. Because sharks have soft cartilage instead
of bones we have not found many well preserved shark fossils. Fortunately,
shark teeth fossilize really well so we have an excellent collection
of their teeth.
largest predatory shark that we know about was called Carcharodon Megalodon,
or the Megalodon Shark. Its teeth look a lot like the teeth of the
Great White Shark but much bigger. We don't know how big it was but it
was probably at least 40ft (13m) long and may have exceeded 80ft (26m).
shark families alive today, the cow sharks (six and seven gilled
sharks) are believed to be the oldest and most primitive. The youngest
family are the strange looking hammerhead sharks.