Secretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland.In contrast to excretion, the substance may have a certain function, rather than being a waste product.ecretion is the process of elaborating, releasing, and oozing chemicals, or a secreted chemical substance from a cell or gland.
The oldest shark fossils. The oldest fossilized evidence of prehistoric sharks comes from shark-like scales that date to 455 million years ago during the Ordovician Period, in Colorado. Some paleontologists do not agree that these scales are sufficiently shark-like to pronounce them sharks.
There are more than 400 different shark species, most of which can be found in coastal regions. They are present in every ocean of the world, with some species also inhabiting rivers. Sharks belong to the class of cartilaginous fish along side rays and chimeras.While the skeleton of all other fish is made of bone, the skeleton of sharks is made of cartilage. Cartilage is lighter and more flexible than bone allowing the shark to make tight turns quickly and to stay afloat.harks are a remarkably diverse group of fish. The largest species â the whale shark â can grow up to 12 meters in length while the smallest species â the dwarf lanternshark â only reaches a size of 17 centimeters.