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Monday, June 13, 2011

The Beuty Of The Horn Shark


Beuty Of Animlas | The Beuty Of The Horn Shark  | The horn shark ( Heterodontus francisci ) is a species of bullhead shark, family Heterodontidae. It is endemic to the coastal waters off the western coast of North America, from California to the Gulf of California. Young sharks are segregated spatially from the adults, with the former preferring deeper sandy flats and the latter preferring shallower rocky reefs or algal beds. A small species typically measuring 1 m (3.3 ft) in length, the horn shark can be recognized by a short, blunt head with ridges over its eyes, two high dorsal fins with large spines, and a brown or gray coloration with many small dark spots.

Slow-moving, generally solitary predators, horn sharks hunt at night inside small home ranges and retreat to a favored shelter during the day. Their daily activity cycles are controlled by environmental light levels. Adult sharks prey mainly on hard-shelled molluscs, echinoderms, and crustaceans, which they crush between powerful jaws and molar-like teeth, while also feeding opportunistically on a wide variety of other invertebrates and small bony fishes. Juveniles prefer softer-bodied prey such as polychaete worms and sea anemones. The shark extracts its prey from the substrate using suction and, if necessary, levering motions with its body. Reproduction is oviparous, with females laying up to 24 eggs from February to April. After laying, the female picks up the auger-shaped egg cases and wedges them into crevices to protect them from predators.

Horn sharks are harmless unless harassed, and are readily maintained in captivity. They are not targeted by either commercial or recreational fisheries, though small numbers are caught as bycatch. In Mexico this species is used for food and fishmeal, and in California its spines are made into jewelry. The International Union for Conservation of Nature (IUCN) does not yet have enough information to determine the horn shark's conservation status. It faces few threats off the coast of the United States.

Like other bullhead sharks, the horn shark has a short, wide head with a blunt snout and prominent supraorbital ridges over the eyes. The horn shark's supraorbital ridges are low and terminate abruptly; the space between them on top of the head is deeply concave. Each eye lacks a nictating membrane and is followed by a tiny spiracle. 

The nostrils are split into inflow and outflow openings by a long flap that reaches the mouth. The inflow openings are encircled by a groove, while another groove connects the outflow openings to the mouth. The mouth is small and curved, with prominent furrows at the corners. There are 19–26 tooth rows in the upper jaw and 18–29 tooth rows in the lower jaw. The teeth at the front of the jaws are small and pointed, with a central cusp flanked by a pair of lateral cusplets; those at the sides of the jaws are much larger, elongated lengthwise, and molar-like.

The body is cylindrical, with two high, somewhat falcate (sickle-shaped) dorsal fins bearing stout spines at the front. The fin spines of reef-dwelling horn sharks are shorter than those living in algal habitats, as their spines become worn down on rocks from the sharks' movements.[3] The first dorsal fin originates over the bases of the large pectoral fins, while the second dorsal fin originates slightly anterior to the free rear tips of the pelvic fins. The caudal fin has a short lower lobe and a long, broad upper lobe with a strong notch near the tip. 

The horn shark's dermal denticles are small and smooth, numbering some 200/cm2 on the back in adults.The dorsal coloration consists of various shades of gray or brown with many small dark spots, though these may be absent in older sharks; the underside is yellowish. There is a dark patch of small spots below the eye. This species may reach a length of 1.2 m (3.9 ft), though most individuals do not exceed 1 m (3.3 ft).
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