Sharks
Sharks are any of the 340 species of fish that, together with the skates, rays, and chimeras, are sharply distinguished from the vast number of bony fish species by their cartilaginous skeletons. Sharks are very keen-sensed fishes, many species of which are able to hunt and eat nearly all the larger water animals in both shallow and deep seas. These two features account for their long evolutionary history. Many of the shark species living today are quite similar to abundant species that swam in seas of the Cretaceous period more than 100 million years ago. Sharks reveal great diversity in behavior and size. The whale shark is the largest shark and also the largest fish in the sea, measuring up to 15-m (49f) in length. The cookie-cutter shark measures less than 50 cm (19in) in length. Sharks are mainly marine fish found in all seas and are especially abundant in tropical and subtropical waters. Many types migrate up rivers. Sharks are best known as aggressive carnivores that even attack members of their own species. Two of the largest sharks-the basking shark and the whale shark-feed on plankton, which they strain from the water with gill rakers. Altogether sharks are very different from other animals because they all ha
ve unique physical characteristics, mating habits, and feeding habits. Unlike bony fish, which usually have great numbers of tiny, immature young, most sharks produce large, well-developed offspring numbering, at the most, 100 to a litter. The sand tiger shark, for example, bears only two young at a time. Fertilization takes place internally, the male inserting one of its claspers into the female. Most sharks produce eggs that develop inside the body of the female. The eggs either hatch inside the female or soon after they are laid. The eggs are often encased in leathery shells with tendrils that anchor them to rocks or weeds. Others have living young that live inside their mother until they are ready to come out. Embryonic development, which is any of the stages of development after fertilization and before giving birth. It takes more than six months for most sharks. At birth, young sharks of some larger species are more than 1m long and are great swimmers that feed on the same prey as adults. The young are frequently born in protected inshore areas away from the males. Sharks commonly fast for long periods during the breeding season and live on the vast reserves of lipids stored in their livers; eating of the young and of one another is thereby avoided. Most sharks are gray in color and have leathery skin covered with small, sharp, pointed scales, which, unlike those of bony fish, do not enlarge during the animals growth. Usually five gills slits lie behind the head. The tail is asymmetrical, with the backbone extended into the upper lobe. Many species have rows of sharp teeth embedded in fibrous membranes instead of in the jawbones. When the sh
Some common words found in the essay are:
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Approximate Word count = 1122
Approximate Pages = 4 (250 words per page double spaced)
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