Mapping the world’s seas and oceans and determining the exact number of the shark species living in them is an on-going project. A few decades ago, scientists believed there are around 400 species of sharks in our seas, but now that estimate is around 500 species.
- The exact number of shark species existing today may not be known, but the species that have already been described can be classified into the following eight orders:
- Angel sharks – relatively large sharks (about 1.5 m long on the average), with a flattened body broadened in the middle and no anal fin;
- Sawsharks – a group characterized by a long snout that is shaped similar to a blade;
- Dogfish sharks – the most common group of all sharks;
- Ground sharks – the largest order of sharks, comprising more than 270 different species;
- Mackerel sharks – this order includes seventeen different species, all of them very special because their body temperature is higher than the temperature in the water around them – a unique feature among sharks;
- Carpet sharks – distinguished by the pattern on their back that makes them look like an oriental rug;
- Bullhead sharks – an order of nine species, all of them featuring a large, bull-like head;
- 6-gilled and 7-gilled species – very large species living in the deep seas.
Shark species vary in every possible aspect of their biology, their lifespan as well as in terms of their habits. Some of them, such as the whale shark, live for more than 100 years, while others, like white sharks, live for only about 20 or 30 years. In terms of body length, most shark species stay in the 1.5 – 2.1 meter range, but there are notable exceptions, such as the pygmy shark that is the smallest of them all, with its body length of only 20 cm or the whale shark, which is the largest species with its 40 ft long body and weight exceeding 2 tons.
Despite the incredible diversity of shark species, there are a number of features that are common to all of them:
They all have skeletons made up of cartilages and not of bones;
They all have multiple gills on the sides of their head, usually 5-7, depending on the species;
Their pectoral fins are not fused with the head;
They all have several sets of teeth that get regularly replaced during their life, so tooth decay is not known to sharks.
Sharks have a very bad reputation of being aggressive and dangerous, but this bad name is given to them mostly by the media and by popular culture. As a matter of fact, out of the hundreds of species in existence, there are only four shark species that are regularly implicated in attacking humans without being provoked: the great white shark, the oceanic white tip, the tiger shark and the bull shark. The other species are relatively tame and many of them are known to like humans, being frequently seen playing around in shallow waters.