All Sharks are Like the Great White!
When you think of a shark, do you think of the great white--enormous, man-eating, dorsal-finned predator of the open sea? While it is true that the approximately 400 described species of sharks have a number of common traits, they in fact exhibit a remarkable diversity.
While many shark species inhabit relatively shallow coastal waters, a number of shark species do occur in the open ocean at depths greater than 1,000 m--these include kitefin sharks (Dalatias licha), lantern sharks (Etmopterus hillianus), catsharks (family Scyliorhinidae), and the Portuguese shark (Centroscymnus coelolepis), which has been found at depths of 3,690 m. Sharks live in tropical and temperate seas, and also inhabit the frigid Arctic regions. Some sharks are even diadromous--that is, they migrate between salt and freshwater habitats.
No shark species subsists solely on vegetable matter, but not all sharks exhibit predatory behavior to obtain food. Some sharks, including the two largest speciesthe whale shark (Rhincodon typus) and the basking shark (Cetorhinus maximus)are filter feeders that eat only plankton. Dentition varies with food type--sharks that feed on mollusks and crustaceans use their flat molar-like teeth for crushing; mako (genus Isurus) and tiger sharks (Galeocerdo cuvier) have long, thin teeth used for piercing and grasping fish and squid; and most requiem sharks (family Carcharhinidae) have serrated teeth that cut their prey.
Morphology and Pigmentation:
Sharks range in size from the small 16 cm, 15 g dwarf dogshark (Etmopterus perryi) to the gigantic 12 m, 12,000 kg whale shark (the largest fish in the world). The angel shark's (Squatina dumeril) body is flattened, allowing it to camouflage itself on the ocean floor, and in this way is convergent with rays. Even the fusiform shape of most sharks varies in proportions. And let's not overlook the strange cranial morphology of the great hammerhead (Sphyrna mokarran). Although sharks do not exhibit the fantastic range of coloration seen in bony fishes, there are many that do vary in color and markings, and some change throughout their life cycles. The zebra shark, for example, is born with strong white stripes over a dark brown background, but as the creature grows, stripes change to brownish spots over a palish, dusky green background. The smalleye hammerhead (Sphyrna tudes) is born orange, changing to yellow as it ages.