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Nurse sharks

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and
Fish

               iNurse sharks
   Ginglymostoma cirratum
   Ginglymostoma cirratum
         Scientific classification

   Kingdom:  Animalia
   Phylum:   Chordata
   Class:    Chondrichthyes
   Subclass: Elasmobranchii
   Order:    Orectolobiformes
   Family:   Ginglymostomatidae
             Gill, 1862

                                   Genera

   See text for genera and species.

   Nurse sharks are cosmopolitan carpet sharks belonging to the family
   Ginglymostomatidae. Common in shallow, tropical and subtropical waters
   of the western Atlantic and eastern Pacific, the family comprises three
   genera each with one species. They are benthic sharks, characterised as
   being sluggish and docile. Nurse sharks typically attack humans only if
   directly threatened.

   The largest species, called simply the nurse shark Ginglymostoma
   cirratum, may reach a length of 4.3 m; the tawny nurse shark Nebrius
   ferrugineus is somewhat smaller at 3.2 m, and the short-tailed nurse
   shark Pseudoginglymostoma brevicaudatum is by far the smallest at just
   75 cm in length. The first of the three species may reach a weight of
   110 kg. Yellowish to dark brown in colour, nurse sharks have muscular
   pectoral fins, two spineless dorsal fins (the second of which is
   smaller) in line with the pelvic and anal fins, and a tail exceeding
   one quarter the shark's body length.

   The mouths of nurse sharks are most distinctive; it is far ahead of the
   eyes and before the snout (sub-terminal), an indication of the
   bottom-dwelling ( benthic) nature of these sharks. Also present on the
   lower jaw are two fleshy barbels, chemosensory organs which help the
   nurse sharks find prey hidden in the sediments. Behind each eye is a
   very small circular opening called a spiracle, part of the shark's
   respiratory system. The serrated teeth are fan-shaped and independent;
   like other sharks, the teeth are continually replaced throughout the
   animal's life.

   Nurse sharks are nocturnal animals, spending the day in large inactive
   groups of up to 40 individuals. Hidden under submerged ledges or in
   crevices within the reef, the nurse sharks seem to prefer specific
   haunts and will return to them every day. By night, the sharks are
   largely solitary; they spend most of their time rifling through the
   bottom sediments in search of food. Their diet consists primarily of
   crustaceans, molluscs, tunicates, and other fish, particularly
   stingrays.

   Nurse sharks are thought to take advantage of dormant fish which would
   otherwise be too fast for the sharks to catch; although their small
   mouths limit the size of prey items, the sharks have large throat
   cavities which are used as a sort of bellows valve. In this way nurse
   sharks are able to suck in their prey. Nurse sharks are also known to
   graze algae and coral.

   The mating season runs from late June to the end of July. Nurse sharks
   are ovoviviparous, meaning the eggs develop and hatch within the body
   of the female, where the hatchlings develop further until live birth
   occurs. The gestation period is six months, with a typical litter of
   30-40 pups. The mating cycle is biennial, as it takes 18 months for the
   female's ovaries to produce another batch of eggs. The young nurse
   sharks are born fully developed at about 30 cm long in Ginglymostoma
   cirratum. They possess a spotted coloration which fades with age.

   The name nurse shark is thought to be a corruption of nusse, a name
   which once referred to the catsharks of the family Scyliorhinidae. The
   nurse shark family name, Ginglymostomatidae, derives from the Greek:
   from gynglimos meaning "hinge" and stoma meaning "mouth".

Genera and species

     * Genus Ginglymostoma
          + Nurse shark, Ginglymostoma cirratum Bonnaterre, 1788
     * Genus Nebrius
          + Tawny nurse shark, Nebrius ferrugineus Lesson, 1831
     * Genus Pseudoginglymostoma (proposed family
       Pseudoginglymostomatidae)
          + Short-tail nurse shark, Pseudoginglymostoma brevicaudatum
            Günther, 1867

   Retrieved from " http://en.wikipedia.org/wiki/Nurse_sharks"
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   with only minor checks and changes (see www.wikipedia.org for details
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