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Guitarfish have a body form intermediate between those of sharks and rays. The tail has a typical shark-like form, but in many species, the head has a triangular, or guitar-like shape, rather than the disc-shape formed by fusion with the pectoral fins found in other rays.
The thresher sharks have an extreme example of this tail in which the upper lobe has evolved into a weapon for stunning prey. Bottom-dwelling sharks such as catsharks and carpet sharks have tails with long upper lobes and virtually no lower lobe. The upper lobe is held at a very low angle, which sacrifices speed for maneuverability.
The pectoral fins have fused to the branchial region of the head, the body begins to gain pigment, and the eyes have developed. When stage four is reached, the embryos still have an external yolk sac, but entirely resemble adults. The dorsal surface is brown and spots on the snout have developed. Claspers in males at this stage also become visible.
The broadnose sevengill shark (Notorynchus cepedianus) is the only extant member of the genus Notorynchus, in the family Hexanchidae.It is recognizable because of its seven gill slits, while most shark species have five gill slits, with the exception of the members of the order Hexanchiformes and the sixgill sawshark.
"We have to think about it in terms of the food web that's out in the ocean: Ultimately, at the very top of that cycle of life are the sharks and if we removed the sharks, smaller fish species ...
While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest.
With his hand close to razor sharp teeth, shark expert Neil Harvey attempts tonic immobility in a large reef shark. Tonic can be induced by turning a shark upside down, but that's not the only way.
Generally, only young sharks are encountered in shallow water, as the adults prefer depths greater than 9 m (30 ft) and is most common at 18–64 m (59–210 ft). [ 1 ] [ 7 ] Blacknose sharks in the South Atlantic Bight (off the Atlantic coast of the southern United States) migrate northward in the summer and southward (or possibly offshore) in ...