The largest whale shark that has been directly measured was reported to be 12.65 meters (41.50 ft) long and weighed more than 21.5 tons.
The body surface is mostly grey (above) and white (below). Three prominent ridges run along the sides and the skin is marked with a checkerboard of spots and stripes which may function as camouflage. The patterns of spots are used to identify sharks from photographs, a method that assumes that they are unique to an individual and that they do not change with age.
The skin of whale sharks is relatively thin, a couple of millimeters, and is covered in tiny teeth-like scales called denticles, which provide a tough, hydrodynamic surface layer. Below the skin is a layer of fatty tissue that can be 10-15 cm thick and is probably important for insulating the shark’s muscles and vital organs.
Whale sharks have two dorsal fins and two lateral pectoral fins. The upper lobe of the tail (caudal) fin of juvenile sharks is larger than the lower lobe compared with adults which have a more crescent-shaped tail.
Spiracles are the small circular openings just behind the whale shark’s eyes. The function of the spiracles of whale sharks is not known. It might be intermediate as whale sharks are more closely related to bottom-dwelling sharks though they also spend substantial time swimming throughout the water column. Consequently the spiracles might function when whale sharks are occasionally stationary but not feeding (when water is passing over the gills).
The mouth of this large filter feeder can be up to 1.5 meters wide. It contains between 300 and 350 rows of tiny scale-like teeth which look like a rasp close-up and account for the species original latin name Rhinodonte, which means rasp-tooth. These teeth do not appear to have function in feeding.
Whale sharks have five large pairs of gills which serve two functions. They extract oxygen from the water to support metabolism and also filter out small prey from seawater.
There are two small eyes located near the front of the wide, flat head. The forward, lateral placement of the eyes allows the sharks to see forward, backward, above and below.
The nostrils are in the front of the head above the mouth and they may have an important function in detection of substances in the water. The large, well developed internal sensory structures connected to the nostrils support this suggestion.
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