SHARK ORDERS

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There are nearly 500 species of sharks.  Sharks are classified into eight orders.  An order is a group of sharks with similar body types.  Orders are than broken down into families, sharks within the order which share similar characteristics. There are 30 families within the eight groups.  Families are than broken down into sets of genera (plural of genus). The species genus forms the first word of its scientific name.  There are 99 genus with in the 8 orders.

Carcharhiniformes
     (Ground Sharks)

The order of the ground sharks consists of 8 families with more than 259 species. More than half of all known shark species are ground sharks. This order also represents the most typical sharks. Their distinguishing features are a nicitating membrane (a flap of skin that functions as a third eye lid), 2 dorsal fins, an anal fin and five gill slits. Most of these sharks are found in tropical and temperate waters. Ground sharks possess all forms of reproduction such as oviparity, aplacental viviparity (ovoviviparity) and viviparity.

Orectolobiformes
     (Carpet Sharks)

This order represents a very diverse group with respect to size and shapes. It consists of 7 families and 13 genera comprising 34 species. Carpet sharks have barbels and spiracles, holes located behind their eyes, to suck in water. This order consists of 5 families with more than 30 species. Assorted members of this group include species such as whale sharks, nurse sharks, and zebra sharks.



Heterodontiformes
     (Bullhead Sharks)

The order of the bullhead sharks comprises one family with only one genus. There are only 9 known species of bullhead sharks. These bizarre looking sharks possess strong spines in front of both dorsal fins. As opposed to the other "spine-wearing" group, the dogfishes, bullhead sharks possess anal fins. As their name implies, their heads look very dominant with big ridges above their eyes, and have a broad snout with very large labial furrows. Based on their heterogeneous teeth (their scientific name "hetero-dontus" stands for different shaped teeth) they are considered as primitive group. Members of this order live only in the waters of the Pacific and Indian Oceans.

Pristiophoriformes
     (Saw Sharks)

Saw sharks (9 species) are a very unusual group that is often confused with sawfishes, which are rays. The most obvious difference between the two is that saw sharks possess barbels and the teeth, located on the prolonged snout, are different sizes. Only five species are known. One species, the sixgil sawshark (Pliotrema warrani), possesses 6 gill slits and lives on the south-eastern Cape Coast of South Africa. Not much is known about the general biology of this order.



Hexanchiformes
     (Frilled and Cow Sharks)

This order is the most ancient one. It consists of 6 species (2 families and 4 genera). The most distinguishable feature is the possession of 6 or even 7 gill slits. This is considered a very primitive feature, as most modern sharks possess only 5 gill slits. Compared to sharks of other orders, frilled and cow sharks only have one dorsal fin.
These sharks have a widespread distribution and live preferably in deeper waters.
The knowledge about their biology is still fragmentary.

Squaliformes
     (Dog Fish Sharks)

This order represents the second largest order and includes 7 families and about 113 species and their most distinguishing feature is the lack of an anal fin. Most species also have a spine in front of the first dorsal fin. The majority are deep water species, and some have luminescent organs. Certain species can reach large sizes for instance the greenland shark, Somniosus microcephalus, with 7 m. Scientists assume that the most abundant species of all known sharks may be the spiny dogfish, (Squalus acanthias), the main species used for "fish & chips".



Lamniformes
     (Mackerel Sharks)

Mackerel sharks consist of 8 families, 10 genera and 17 species. They are a rather diverse group that lack a singular distinguishing characteristic and for the identification a combination of different features is needed such as: Origin of mouth behind the eyes, conical snout, a pair of 5 gill slits, 2 dorsal fins and no nicitiating membrane. Many of the sharks possess a counter-current circulatory system. This system enables them to maintain a higher body temperature and live in colder waters. Mackerel sharks include the biggest and fastest predators like White Sharks or Makos. Most Mackerel sharks can raise their body temperature by means of a heat exchange system (rete mirabilis).

Squatiniformes
     (Angelsharks)

Like saw sharks, angel sharks are also often misidentified as rays. The most obvious difference is that angel sharks possess pectoral fins that are not attached to or connected with the head. Angel sharks also possess an enlarged caudal lower lobe but, like dogfishes, do not possess anal fins. This order includes 18 species, most of them of small size. An exception is the japanese angel shark, Squatina japonica, that reaches 2 m. Unique in angel sharks is that the lower lobe of the tail is longer than the upper lobe. Angel sharks spend most of the day buried in sand ranging from very shallow water to 1300 m.



            
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