Friday, March 20, 2009

Stingray

Stingrays are much feared venomous fishes in the subfamily Dasyatinae, family Dasyatidae. They are flattened like other rays and posses broad, winglike pectoral fins, which they flap in swimming. The tail is long and whiplike and bears two strong spines at its base. The stingray usually lies partly buried in the sand. If in stepped on or seized, it lashes out vigorously with its tail and attempts to drive a spine into the intruder. The spines are tempts to drive a spine into the intruder. The spines are derivatives of the scales and are associated with poison glands; they are serrated and solid, thus cutting and tearing the flesh as well as injecting poison. The wound can be extremely painful, and the powerful poison, apparently a protein, affects the heart and the nervous system of mammals and can cause depressed respiration.

The head of the stingray is not well defined, and there is no dorsal or caudal fin. The skeleton is composed of cartilage. The gill openings are ventral, with water being taken in through paired spiracles behind the eyes. The ventral mouth has numerous small, blunt teeth. Small clams, crustaceans, and other invertebrates are caught as food when the ray digs a broad depression in the sand. The stingray is ovoviparous; the female carries eggs internally but does not nurture the fetuses, and the young are born alive. Stingrays are widely distributed in warm, shallow seas, and a few species ascend rivers in South America. They occur along the Atlantic coast of the United States as far north as Cape hatteras. Some species may reach more than 1.5 m (5 ft) across. Stingrays may weigh from 0.7 to 340 kg (1.5 to 750 lb).

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