Fish and Amphibians

Phylum Chordata The phylum Chordata includes fish, amphibians, reptiles, birds, mammals and a few invertebrate classes. They are placed in this phylum because they all have a notochord.

Invertebrate Chordates The simplest chordates are the tunicates and the lancelets. They both have a notochord in their larval stage. Lancelets Tunicate

Subphylum Vertebrata The remainder of the organisms belong to the subphylum Vertebrata. They all have vertebrae surrounding their spinal chord, an endoskeleton, most have a hinged jaw.

Classification Kingdom Animalia Phylum Chordata Subphylum Vertebrata Classes Agnatha Chondrichthyes Osteichthyes Amphibia

Agnatha: Jawless Fish Examples: sea lamprey, hagfish Characteristics: Lack jaws, cartilage skeleton, no scales, unpaired fins, cold blooded (ectothermic).

Chondrichthyes: cartilage fish Examples: sharks, skates, and rays Characteristics: Cartilage skeleton, moveable jaws, paired fins, placoid scales, internal reproduction, cold blooded.

Shark Reproduction Sharks are ovoviviparous. That means that they have internal reproduction, have eggs that hatch inside the mother and then the babies are born alive.

Identification of male sharks

Osteichthyes: bony fish Examples: trout, salmon, lung fish, Ceolacanth Characteristics: Bony skeleton, paired fins, moveable jaws, swim bladder, bony scales, indirect external reproduction, cold blooded and a lateral line system.

Classification of Bony Fish Lung Fish – are fish that have a pouch branched off from the esophagus. It is a very primitive lung. This is not very efficient but they can survive during droughts by digging into the mud, breathing slowly until the rains come.

Lungfish in mud

Lobed Finned Fish One living species: Ceolacanth The Ceolacanth has bones in its fins. These fish are common in the fossil record.

Ceolacanth

Ray Finned Fish These bony fish have rays in their fins. Most fish belong to this class.

Reproduction Fish reproduce by indirect external reproduction. The female prepares a nest, lays her eggs in the nest and then the male squirts sperm over the top of the egg pile. Not all of the eggs get fertilized.

Amphibians Examples: Frogs, salamanders, toads, newts… Characteristics: Moist thin skin, lungs as an adults: gills as a larva, two chamber heart as larva: three as adult, Must lay eggs in water (no shell on eggs), toes with no claws, no scales, tympanic membrane, direct external fertilization and cold blooded (ectothermic).

Larva The larva stage of an amphibian has a two chamber heart, fins, gills.

Classification of Amphibians Frogs and Toads belong to the order Anura. They have large hind legs and no tail. They must go back to water to lay their eggs (except as few toads).

Urodela Salamanders and Newts belong to the order Urodela. They have tails, long slender bodies and equal sized legs. Some like the mudpuppy keep gills their whole life.

Apoda The order Apoda are the legless amphibians. They live in tropical regions and live in moist soil.

Reproduction Amphibians reproduce by direct external reproduction. In a hold called amplexus, the male, on the back of the female, pushes the eggs out of the female and fertilizes each egg as it passes out of the female.

Metamorphosis All amphibians go through some type of metamorphosis. This is the change from an egg, to a larva (tadpole) to an adult.

Pollution Amphibians are very sensitive to pollution. Worldwide the number of amphibians is decreasing. Pollution kills them and can cause strange mutations. Radiation getting through the ozone layer causes damage to the embryos.

Other problems