The sharks, rays, and skates (which are similar to stingrays) are further broken into two superorders: 1. Rays and skates. 2. Sharks. Sharks are some of the most frequently studied cartilaginous fish. Sharks are distinguished by such features as: The number of gill slits. The number and type of fins. The type of teeth. The size of their jaws. Body shape. Their activity at night. An elongated, toothed snout used for slashing the fish that they eat, as seen in sawsharks. Teeth used for grasping and crushing shellfish, a characteristic of bullhead sharks. A whisker-like organ named barbels that help sharks find food, a characteristic of carpet sharks. A long snout (or nose-like area), characteristic of groundsharks. Ovoviviparous reproduction, where the eggs develop inside the mothers body after internal fertilization, and the young are born alive. This trait is characteristic of mackerel sharks. All sharks mate by internal fertilization. Some sharks then lay their eggs, others allow internal development.
blood skin and teeth
Since they do not have bone marrow (as they have no bones), red blood cells are produced in the spleen, in special tissue around the reproductive organs, and in an organ called Leydigs organ, only found in cartilaginous fishes. The tough skin of this group of fish is covered with placoid scales, which are hard scales formed from modified teeth. The scales are covered with a hard enamel. The hard covering and the way the scales are arranged, gives the fish skin rough, sandpaper-like feel. The function of these scales is for protection against predators. The shape of sharks teeth differ according to their diet. Species that feed on mollusks and crustaceans have dense flattened teeth for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey, such as mammals, have pointed lower teeth for gripping and triangular upper teeth with serrated edges for cutting. Sharks continually shed and replace their teeth, with some shedding as much as 35,000 teeth in a lifetime.
The 1,000 or so species of cartilaginous fish are subdivided into two subclasses: the first includes sharks, rays, and skates; the second includes chimaera, sometimes called ghost sharks. Fish from this group range in size from the dwarf lanternshark, at 6.3 inches, to the over 50-foot whale shark. Sharks obviously have jaws, as do the other cartilaginous fish. These fish evolved from the jawless fish. So why did fish eventually evolve to have jaws? Such an adaptation would allow fish to eat a much wider variety of food, including plants and other organisms. Other characteristics of cartilaginous fish include: Paired fins. Paired nostrils. Scales. Two-chambered hearts. Skeletons made of cartilage rather than bone. Cartilage is supportive tissue that does not have as much calcium as bones, which makes bones rigid. Cartilage is softer and more flexible than bone.
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the cartilaginous are the first fish with a bony skeleton.
a. true --> b. false
the cartilaginous fish are the first fish with jaws.
--> a. true b. false
which of the following are characteristics of cartilaginous fish?
a) a two-chamber heart b) paired fins c) paired nostrils --> d) all of the above
some sharks have ovoviviparous reproduction. what is ovoviviparous reproduction?
a) when the egg is laid after fertilization. b) when the egg is laid and fertilized externally. --> c) when the baby is born alive. d) none of the above
what are two ways sharks can be distinguished?
a) the number of gill slits and the type of teeth b) the number of fins and their body shape c) the type of fins and their activity at night --> d) all of the above are ways to distinguish sharks.
what are barbells in sharks?
a) muscles around the jaws that allow for rapid contraction. b) whisker-like organs that help sharks sense predators. --> c) whisker-like organs that sense the environment to help the sharks find food. d) organ that produces red blood cells
what is leydigs organ?
a) the organ that helps sharks and rays sense predators. --> b) the organ that produces red blood cells. c) the organ that helps sharks and rays find food, d) the organ that replaces lost teeth.
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