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Scientific name........Megachasma Pelagios
The Megamouth shark was recently discovered in 1976 off Hawaii and therefore a new genus, species, and family of vertebrates was created known as the Megamouth shark. Its scientific name comes from the Greek to mean "giant yawner of the open sea".
They are a huge shark with a large, wide, long head, short snout and a huge mouth extending behind the eyes. It has a flabby body, soft fins, asymmetrical tail, and a lack of keels. It has elongated pectoral fins, the gill slits are moderately long and are lines with dense, fingerlike dermal papillae.
The largest size of the megamouth shark reported was 18 feet, the size of some females have been reported at 12 feet and 16 feet and males at 6 feet and 13 feet. Size at birth unknown.
For the size of the megamouth shark, their teeth are very small but plentiful, there are approximately fifty rows of teeth and relatively numerous on each jaw. The upper and lower jaws have a symphyseal ( where the two halves of the jaw meet ) is a toothless space, but it is larger in the upper jaw. A difference between the upper and lower teeth was recognized on a female specimen. The first five upper teeth are smaller than the first five lower teeth; the more distal upper teeth are smaller than the lower teeth; the cusps of the lower teeth are more acute and longer than those of the upper teeth.
These sharks are a gray to blackish brown color on the dorsal surface ( light margins to blackish pectoral and pelvic fins. ) and white on the ventral surface. Dark spotting on lower jaw. Mouth roof on dorsal and lateral parts, and oral membranes, silvery. Tongue purplish brown with slight silvery tint on both sides, dorsally and ventrally. Both sexes seem to have a white band on the anterior surface of the snout. This white band could be considered a feeding bechacioral characteristic, because it is so contrasted by the dark coloration of the snout and upper jaw, and becomes very prominent when the upper jaw is protruded. Probably under low light this white band may be more visible. This band might also be related to recognition of other individuals of the same species.
It appears to be a plankton feeder, like the whale shark and the basking shark. It swims slowly through the open ocean, filtering small shrimps and other prey from the water as it goes. It spends the day feeding in deep water and comes up to shallower water at night. The silvery lining of its mouth cavity is probably reflective, so that when shrimps and luminous crustaceans enter the open, cavernous mouth, they may encourage others to enter possibly by suction.
This species is presumed to be a verticle migrator on a diel cycle, ( spending the daytime in deep waters and ascending to midwater depths at night ). This verticle migration may be a response to the movements of the small animals on which it feeds. The krill that make up part of megamouth's diet are known to migrate from deep waters to the surface. Almost all megamouth sharks reported presented scars in different parts of the body. These scars are considered bite marks of the cookiecutter shark and with similar verticle migrator patterns the megamouth combined with its slow swimming speed it would make it an easy target for the active cookiecutter.
Megamouth sharks are found throughout the word's oceans, often at great depths. From confirmed sightings this species is now known from India, Pacific and Atlantic Oceans. By tagging some individuals they were able to demonstrate that this species engages in vertical migrations on a diel cycle.
Reproduction is unknown, although presumed viviparous with oophagy.
The Megamouth shark is considered to be less active and a poorer swimmer than that of the basking shark and whale shark. Their poor mobility likely a reflection of its flabby body, soft fins, asymmetrical tail, lack of keels and weak calcification.
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