Sharks

A detailed Summary of Sharks

Sharks are commonly defined as a marine fish of the order Squaliformes or Selechii. They make up the Chondrichthyes, or "cartilaginous fish" along with skates, rays, and a few other fish. Members of the Chondrichthyes lack true bone and have a skeleton made of cartilage. Only their teeth, and sometimes their vertebrae, are calcified, but this is still not true bone. The bone structure is one of the main differences that separates sharks from other fish and marine animals. Sharks also differ in that they have a skull without sutures and reserve rows of teeth attached to the skin of the jaws. They lack an air bladder forcing all but shallow-water forms to swim constantly in order to keep from sinking.

When looking at sharks there are eight orders and about 350 species so it is difficult to discuss each one in detail. All sharks are Selachians and are characterized by a fusiform body with five to seven pairs of lateral gill slits. Sharks are easily identified by distinctive characteristics such as a ventrally positioned mouth, an asymmetrical tail with the vertebral column extended into the upper lobe, and a body covered with tiny, sharply pointed placoid scales. Sharks are found at all depths of all the oce

http://www.ucmp.berkeley.edu/vertebrates/basalfish/chondrintro.html

As for reproduction and behavior, sharks vary from species to species. Some species lay eggs encased in leathery shells, usually with tendrils that anchor them to rocks or vegetation. Others have eggs that develop within the females' uteri, and the young are born alive. Other species have a method similar to mammals, in which the young develop in utero and are nourished by maternal blood delivered through an umbilical stalk from a placenta. Gestation varies greatly with sharks, from a few months to more than two years. A difference between sharks and bony fish is that the bony fish lay enormous numbers of tiny eggs that develop into minute young, sharks produce small numbers of large young. At birth sharks are completely developed and have no parental care. Some sharks, such as the great white, are loners and seemingly swim at random, although they sometimes gather to feed. Other sharks gather in schools, while some school only for migrations.

One of the greatest enemies to sharks today are over fishing and bycatch. These two problems have seriously damaged the shark population, mainly because of the shark reproduction rate. Another enemy is fishing tournaments. Fisherman are limited now to the amount of sharks they can catch by species. There are no large short fin makos or whites left, or at least none like the giants that swam the seas before man figured out how to fish with high tech lures, rods, and reels. Sharks are usually caught for sport, to be stuffed and hung on walls, and to sell their teeth, none

Some common words found in the essay are:
Selechii Chondrichthyes, Sharks Sharks, bony fish, true bone, eggs develop, gill slits, species species,

Approximate Word count = 1084
Approximate Pages = 4 (250 words per page double spaced)

Category: Science