by L.S. Watts

Created on: August 05, 2009

When a person thinks shark they probably think of the menacing great white shark or the odd shaped hammerhead shark. What many people don't realize is that there are 360 different species of sharks in the world. These sharks are then classified into eight different orders.

Hexanchiformes

The sharks in this order are considered the most primitive. In fact, aside from the cow shark and the frill shark many of the sharks in this order are now extinct. The sharks left in this order have six to seven gills and only one dorsal fin. What the sharks in this order are lacking is nictitating membrane in the eyes.

Squaliformes

Bramble shark, rickly shark, dog fish shark, and roughshark are a few of the 80 species of sharks listed in this order. These sharks are known have five pairs of gills and two dorsal fins. However, they do not have an anal nor do they have nictitating membranes in their eyes.

Pristiophoriformes

Eight species of saw sharks occupy this order. They have five to six pairs of gills and two dorsal fins. They have notably large nasal barbells on the ventricle side. These sharks do not have an anal fin.

Squatiniformes

Angel sharks make up the sharks in this order. With nineteen species of angel sharks, squatiniformes have five pairs of gills on the ventricle side and no anal fin. There are two dorsal fins and the lower lobe of the caudal fin is larger than the upper lobe.

Heterodontiformes

Heterodontiformes consist of nine species of bullhead sharks. These sharks are smaller than most sharks and are considered bottom feeders. The largest species in this order only grows to a length of 59 inches which are located in tropical and subtropical waters. Theses sharks have two dorsal fins and an anal fin. This is also another order where the sharks do not have nictitating membranes in their eyes. The sharks of this order have five pairs of gills.

They are also unique because they have a different type of teeth than other sharks. They have molar like teeth for crushing and chewing prey. Other shark groups have some form teeth in the front row used for grabbing prey but the heterodontiforme sharks do not have this feature.

Orectolobiformes

Commonly referred to as carpet sharks, orectolobiformes have thirty-five species in this order. Some of these species include zebra sharks, nurse sharks, and even whale sharks. Each shark has two spineless dorsal fins. Most orectolobiformes have five pairs of gills with the fourth gill overlapping the fifth gill.

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