FISHES, AMPHIBIANS, AND REPTILES Characteristics of Chordates and Vertebrates Fish, amphibians, and reptiles are part of a group of animals called vertebrates. All vertebrates are part of the phylum Chordata and the subphylum Vertebrata. Chordates Organisms within the phylum Chordata are called chordates. All chordates have three common characteristics at one point in their life cycle. These characteristics are: pharyngeal slits in their throat area, a notochord, and a nerve cord. A notochord is a rod that is flexible and supports the organism’s back. Most organisms that are vertebrates replace the notochord with a backbone, or spine. Some species have cartilage instead of bone. Cartilage is connective tissue that is flexible and strong, but softer than bone. The nerve cord found in chordates develops into a spinal cord that is part of the nervous system. Humans have a nerve cord called the spinal cord that runs through the backbone. In humans, information travels along the nerve cord from the body to the brain and back. Chordates also have pharyngeal slits at some point in their lives. The pharynx is part of the throat, just behind the mouth. In fish, the pharyngeal slits turn into gills, but in humans the pharyngeal slits disappear before birth. © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Lesson Checkpoint: What is a notochord? What are pharyngeal slits? Vertebrates Vertebrates are chordates that develop backbones. Mammals, birds, amphibians, reptiles, fish, sharks, and rays are all groups, called classes, of vertebrates. Backbone Development: In all vertebrate species, the notochord develops into a backbone made of vertebrae. Vertebrae are many small bones that are lined up in a row that come together to form the backbone. The vertebrae are flexible because there are joints in between the vertebrae. Each of the vertebrae has a hole in the center where the spinal cord runs through. The backbone protects the spinal cord. The backbone is a part of a vertebrate’s endoskeleton, which supports, gives protection and shape to the body, and provides a surface for muscle tissue to attach. Important characteristics of the endoskeleton of vertebrates are that it: • grows as the organism grows, • supports the pull of gravity, and • allows the organism to move easily. Lesson Checkpoint: What do the vertebrae protect? Body Temperature Control: Vertebrates are also grouped according to the way in which their body temperature is controlled. Fishes, amphibians, and reptiles are ectotherms. An ectotherm is an animal with an internal temperature that is controlled by the environment in which it lives. Ectotherms produce © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
very little heat within their bodies. A lizard will sun bathe on a cool desert morning in order to raise its body temperature. The opposite of an ectotherm is an endotherm. An endotherm controls the internal temperature by producing heat, making it nearly the same temperature inside its body at all times. Humans are endotherms. Lesson Checkpoint: What is an endotherm? What is an ectotherm? Fish Gills: Fish use gills to obtain oxygen from the water environment in which they live. The water comes in through the mouth and moves through slits in the throat where it is channeled across the gills. In the gills, the carbon dioxide waste is exchanged for oxygen. Circulatory System: Fish have a closed-circulatory system, allowing blood to reach the cells of the body through blood vessels. Blood moves one-way through the blood vessels from the heart, to the gills, and on to the cells of the body. Reproduction: Fish reproduce using external fertilization. External fertilization is when the female’s eggs are meeting with the male’s sperm outside of the female’s body. Lesson Checkpoint: What is external fertilization? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Classification: Scientists classify fish into three major groups. They are the jawless fish, cartilaginous fish, and bony fish. The oldest of all vertebrates are the jawless fish. • Jawless Fishes: Jawless fish are the only fish that do not have scales. Their fins are not paired and their skeletons are made of cartilage. Most importantly, jawless fish are not able to bite because, as their name states, they are jawless. Instead, they feed by sucking, stabbing, and scraping their food. There are two types of jawless fish: hagfish and lampreys. • Cartilaginous Fishes: Cartilaginous fishes include rays, sharks, and skates. Just like the skeletons of the jawless fishes, the cartilaginous fish skeletons are made of cartilage. The major difference between the two groups is that the cartilaginous fish have jaws that they can use to bite. They also have fins that are paired. Cartilaginous fish are all carnivores that hunt for food. The majority of sharks are unable to pump water over their gills, so they are only able to sleep in ocean currents. The currents force the water over their gills. When they are not sleeping in the ocean’s currents, they must keep moving so that they are constantly getting the oxygen they need. • Bony Fish: The bony fish are the fish that we know best. They have bodies that are covered with scales and movable flaps that open and close to control the water flow over their gills. The majority of species of bony fish have an organ called a swim bladder. The swim bladder is a gas-filled sac that stabilizes the fish’s body at different depths in the water. The amount of gas that is in the swim bladder is controlled by the fish and can be adjusted by the fish. Bony fishes are the most abundant of all the fishes and vary drastically in their physical characteristics. Lesson Checkpoint: What are the three major groups of fish? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Amphibians An amphibian is a vertebrate that is ectothermic. Most amphibians live the beginning of their lives in the water. Once they reach adulthood, they live on land, only to return to the water to reproduce. Life Cycle: Amphibians lay eggs in the water, where the eggs hatch into larvae. The larvae have gills and undergo metamorphosis when entering the adult phase. Circulatory System: The circulatory systems of tadpoles and frogs vary. The tadpole has a single loop system, while the adult frog has a double looped system. Most amphibians’ hearts consist of three chambers. The atria are the upper two chambers of the heart, while the lower or center chamber is the ventricle. The oxygen-rich blood and oxygen-poor blood enters the heart through the atria. The blood then moves into the ventricle of the heart where the oxygen-rich and oxygen-poor blood mix together and is pumped back through the circulatory system. Lesson Checkpoint: What is the role of the atria and the ventricle in an amphibian’s heart? Types of Amphibians: Examples of amphibians include frogs, toads, and salamanders. The adult skeletons of most amphibians are strong with muscular limbs, which they adapted for better movement on land. Lesson Checkpoint: What are some examples of amphibians? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.
Reptiles A reptile is a vertebrate that is ectothermic and has scaly skin and a pair of lungs. Lizards, snakes, turtles, tortoises, and crocodiles are all examples of reptiles. Adapted for Life on Land: A reptile has the ability to spend its entire life on land. Land animals can be considered similar to a water balloon. They hold water inside of the body. Adaptations of land animals for conserving water include eggs, skin, and kidneys. The eggs of reptiles are internally fertilized. After fertilization, the egg forms a membrane and a shell that surrounds the embryo. The membrane and shell protect the egg and keep it from losing water. This allows reptiles to lay their eggs on land. Lesson Checkpoint: What two features of a reptile’s egg enable it to survive on land? The skin of reptiles is tough and is covered with scales, which keeps water inside of their bodies. The kidneys of reptiles filter wastes to be excreted by the body in watery liquid called urine. The kidneys keep the majority of water inside of the body while filtering the wastes. Lesson Checkpoint: What three adaptations of land animals help them keep water in their bodies? © Copyright NewPath Learning. All Rights Reserved. Permission is granted for the purchaser to print copies for non-commercial educational purposes only. Visit us at www.NewPathLearning.com.