Jawless and Cartilaginous Fishes

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

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

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

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

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

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

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

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

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

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 Adaptations of Cartilaginous Fishes

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