Jawless and Cartilaginous Fishes

1. Jawless and Cartilaginous Fishes

2. Jawless Fish • The only existing Jawless fish are hagfishes and lamprey • Jawless fish’s skin has neither plates nor scales • The bodies of hagfish and lamprey are eel-like, have a cartilaginous skeleton, unpaired fins, and the notochord remains throughout their lifetime

3. Hagfishes • They are bottom dwellers that live only in cold marine waters • Hagfish do not have vertebrae • Hagfish are isotonic • This means their body fluids have the same ion concentration as sea water • Hagfish feed on small invertebrates and dead and dying fish • Within its mouth are two moveable plates and a rough tonguelike structure it uses to pinch off chunks of flesh • Since they lack fins they often borrow into the body of a dead fish and once inside they will eat their internal organs

4. Lampreys • About half of adult lampreys are non-parasitic, and the other half are parasites that feed on the blood and body fluids of other fish • Lampreys use their disk-shaped mouths to attach to its host • It then scrapes a hole in the host’s body with its rough tongue and secretes a chemical that keeps the host’s blood from clotting • Once it is done feeding it drops off the host and the host may recover, bleed to death, or die from infection • Lampreys can live in salt and fresh water, but all lampreys breed in fresh water • Reproduction takes place in the form of external fertilization

5. Cartilaginous Fishes • Made up of sharks, skates, and rays • The fish in this class have skeleton composed of cartilage, which is a flexible lightweight material made of cells surrounded by tough fibers of protein • Unlike jawless fish, they have movable jaws, skeletons, and paired fins • They all live in saltwater and are carnivores • Some cartilaginous fishes are also scavengers • The skin of cartilaginous fishes is covered in placoid scales • They are small toothlike spines that feel like sand paper • They are thought to reduce turbulence of the water flow and thus increase swimming efficiency

6. Sharks • Sharks have a fusiform body shape, which is a smooth, torpedo-shaped body , that reduces turbulence when swimming • The largest sharks, the whale shark and basking shark , feed on plankton and floating plants and animals • Like other filter feeding fish they have gill rakers to help filter the water

7. Sharks • The mouth of a typical shark has 6 to 20 rows of teeth • When a tooth breaks or wears down a replacement tooth moves forward to take its place • Sharks may use up to 20,000 teeth over its lifetime • The structure of each species’ teeth has been adapted to that species’ feeding habits • Example: Sharks that eat large fish or mammals have big, triangular teeth with sawlike edges that hook and tear flesh

8. Rays and Skates • Rays and Skates have flattened bodies with paired winglike pectoral fins, and in some species whiplike tails • Rays have diamond or disk shaped bodies, while skates have triangular bodies • Rays and Skates are less than 1 meter long • They both are primarily bottom dwellers • Their flat shape and coloration camouflage them against the floor of their habitats • They feed on mollusk and crustaceans

9. Adaptations of Cartilaginous Fishes • Gas exchange: occurs in the gills, which lie behind the head • Fast-swimming sharks push water through their mouths, over their gills, and out their gill slits by swimming • Most cartilaginous fish pump water out of their gills by expanding and contracting their mouth cavity and pharynx • Rays and skates draw water through their spiracles, which are two large openings on the top of their head behind their eyes

10. Adaptations of Cartilaginous Fishes • Elimination of Waste: Instead of releasing ammonia cartilaginous fishes use energy to convert ammonia into a compound called urea • Sharks retains large amounts of urea in their blood and tissues, which raises the concentration of solutes in their body to the same level of that found in water • The concentration of sodium and chloride in a shark’s body is less than the concentration found in sea water, therefore these ions diffuse into the body across the gills and are absorbed with food • The rectal gland removes excess sodium and chloride ions from the blood and releases them to the rectum for elimination

11. Adaptations of Cartilaginous Fishes • Cartilaginous fishes maintain their position in the water in two ways: • 1. The caudal and pectoral fins generate lift as the fish swims and it can remain at the same level in the water as long as it keeps moving • 2. The storing of large amounts of low-density lipids in their livers. The lipids give sharks buoyancy by reducing the overall density of the body

12. Reproduction in Cartilaginous Fishes • Fertilization occurs inside the female’s body (Internal Fertilization) • Internal Fertilization occurs when the male transfers sperms into the female using modified pelvic fins called claspers • Young are born in three ways • 1. After fertilization the female lays large yolky eggs • 2. The eggs develop inside the females body and the young are born alive • 3. The mother nourishes the developing sharks while they are in her body • No cartilaginous fish provide parental care for their young after they are born or hatched