Shark

Shark
Oceanic whitetip shark (Carcharhinus longimanus)
Scientific classification
Kingdom Information
Domain	Eukaryota
Kingdom	Animalia
Subkingdom	Biliteria
Branch	Deuterostomia
Phylum Information
Phylum	Chordata
Sub-phylum	Vertebrata
Infraphylum	Gnathostomata
Class Information
Class	Chondrichthyes
Sub-class	Elasmobranchii
Order Information
Superorder	Selachimorpha
Population statistics

Sharks are approximately 350 species of cartilaginous fish of the order Selachimorpha, inhabiting the world's oceans and several freshwater lakes and rivers.

Description

Sharks vary in appearance, shape, and size, so there is no absolute description of a typical shark. In general, all sharks with several exceptions share the following characteristics:

• A skeletal system made entirely of cartilage, with the vertebrate extending to and forming the claudal (tail) fin's upper lobe.
• A ventrally-located mouth with the upper jaws unattached to the skull, enabling the animal to extend both jaws forward to take in prey.
• Skin covered with denticals, a type of placoid scale rough to the feel and related to teeth.
• Teeth arranged in a "conveyor belt"-fashion, enabling continual replacement over the lifetime of the animal.

Orders and Families

Squaliformes

Dogfish; order representing 7 families and 113 species of shark, with the spiny dogfish possibly the most abundant fish of any kind in the world's oceans. They are characterized by a lack of an anal fin, and range in size from 7.5 inches (Dwarf lanternshark, Etmopterus perryi) to 21 feet (Greenland shark, Somniosus microcephalus).

• Bramble sharks (Echinorhinidae, 2 species)
• Dogfish (Squalidae, 20 species)
• Roughsharks (Oxynotidae, 5 species)
• Gulper Sharks (Centrophoridae, 15 species)
• Lantern Sharks (Etmopteridae, 51 species)
• Sleeper sharks (Somniosidae, 18 species)
• Kitefin sharks (Dalatiidae, 10 species)

Hexanchiformes

Deep-water sharks, identifiable by the presence of six or seven gill slits (cow sharks); or a shape reminiscent of an eel (frilled sharks)

• Frilled sharks (Chlamydoselachidae, 2 species)
• Cow sharks (Hexanchidae, 3 species)

Pristiophoriformes

Sharks identified by a long snout bearing variably-sized teeth on either side, similar in appearance to sawfish.

• Sawsharks (Pristiophoridae, 6 species)

Squatiniformes

Identified by their flattened, ray-like appearance, lack of anal fins, and the lower lobe of the tail fin longer than the upper lobe.

• Angelsharks (Squatinidae, 16 species)

Heterodontiformes

Sharks which have a characteristic pig-like snout, short face, and bovine-like ridges above the eyes. All species have a spine in front of their dorsal fins.

• Bullhead sharks (Heterodontidae, 9 species)

Orectolobiformes

Carpet sharks, so-named for the intricate patterns resembling oriental carpeting. Most species are small bottom dwellers; the exception is the whale shark (Rhincodon typus), at up to 60 feet in length it is the largest living fish.

• Collared carpetsharks (Parascyllidae, 8 species)
• Blind sharks (Brachaeluridae, 2 species)
• Wobbegongs (Orectolobidae, 12 species)
• Bamboosharks (Hemiscyllidae, 16 species)
• Zebra shark (Stegostomatidae, 1 species)
• Nurse sharks (Ginglymostomatidae, 3 species)
• Whale shark (Rhiniodontidae, 1 species)

Lamniformes

Mackerel sharks. Most species identified by a robust appearance; all lack a nictating membrane over the eyes.

• Sandtigers (Odontaspididae, 4 species)
• Goblin shark (Mitsukurinidae, 1 species)
• Crocodile shark (Pseudocarchariidae, 1 species)
• Megamouth shark (Megachasmidae, 1 species)
• Thresher sharks (Alopiidae, 3 species)
• Basking shark (Cetorhinidae, 1 species)
• Mackerel sharks (Lamnidae, 5 species)

Carcharhiniformes

Ground or common sharks, characterized by a nictating membrane over the eyes; several species have been implicated in attacks on man.

• Catsharks (Scyliorhinidae, 150 species)
• Finback catsharks (Proscylliidae, 7 species)
• False catsharks (Pseudotriakidae, 4 species)
• Barbelled houndshark (Leptochariidae, 1 species)
• Houndsharks (Triakidae, 40 species)
• Weasel sharks (Hemigaleidae, 8 species)
• Requiem sharks (Carcharhinidae, 52 species)
• Hammerhead sharks (Sphyrnidae, 9 species)

Behavior

Many species of sharks give birth to a few dozen live young, others lay a similarly small number of eggs; these are often washed ashore and are known as mermaid's purses.

Sharks are reputed to be able to detect minute amounts of blood in water, and to be able to follow blood trails for miles. In fact, although sharks can detect blood at concentrations of as little as a few parts per billion, a very considerable quantity must be spilt before it is detectable amongst billions of gallons of seawater. Sharks actually use sounds and vibrations to locate most of their prey.

Classification

Sharks belong to the holobaramin that also includes skates and rays.

Environmental Concerns

Worldwide, sharks suffer threats from over-fishing, mercury poisoning, ocean acidification, and habitat disruption. . Many individual shark species are currently threatened or endangered, often because of human activities such as careless fishing practices and coal fired plants dumping tones of toxic mercury into the oceans.