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
It swims a short distance away, waiting for its victim to bleed to death. On the other end, the smallest shark, the cigar shark, is only 15 to 20 cm (6-8 inches). Some species lay eggs encased in leathery shells, usually with tendrils that anchor them to rocks or vegetation. This species feeds solely on plankton and small fish. These two problems have seriously damaged the shark population, mainly because of the shark reproduction rate. Fins are sold to restaurants and also are thought to be a cure for impotence, though nothing has been proven. The eyes, which are lateral, are highly sensitive to contrasts of light and shadow and are especially adapted to see in dim light. If this shark sees a shape resembling that of a seal, it will make a full speed charge at that shape. They are the most abundant in tropical and subtropical waters. As for reproduction and behavior, sharks vary from species to species.
Common topics in this essay:
Selechii Chondrichthyes,
Sharks Sharks,
bony fish,
true bone,
eggs develop,
gill slits,
species species,
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