CLASS AMPHIBIA - AMPHIBIANS
These animals live a "double life", both on land and in water. They are gill and lung breathers. Unable to regulate body temperature. Limited to freshwater lakes, streams and ponds. Since gas exchange occurs in their skin, their skin must stay moist. Wide variety of shapes and colors. Salamanders, frogs, toads.
REPRODUCTION
Sexual. Fertilization is internal (in which case sperm enters the female's cloaca, which holds the eggs) and external; both of which have to occur in extremely moist or damp environments; otherwise, the eggs will dry up and die. Females mostly lay eggs in the water to be fertilized by the male sperm. These eggs have no covering to prevent the eggs from drying up. But, they are covered in a sticky substance that keeps them anchored to the water. A tadpole changes from a gill-breathing, legless herbivore with fins and a two-chambered heart into a lung-breathing, four legged-carnivore with legs and a three-chambered heart.
CIRCULATORY SYSTEM
Closed circulatory system. This circulatory system consists of a double loop. The first loop moves oxygen-poor blood from the heart to pick up oxygen in the lungs and in the skin and then moves the oxygen-filled blood back to the heart. In the second loop, blood filled with oxygen moves from the heart through vessels to the body, where the oxygen diffuses into cells. The heart is 3-chambered with two atria (right atrium receives deoxygenated blood from body; left atrium receives oxygenated blood from the lungs) and one ventricle, which remains undivided.
REPRODUCTION
Sexual. Fertilization is internal (in which case sperm enters the female's cloaca, which holds the eggs) and external; both of which have to occur in extremely moist or damp environments; otherwise, the eggs will dry up and die. Females mostly lay eggs in the water to be fertilized by the male sperm. These eggs have no covering to prevent the eggs from drying up. But, they are covered in a sticky substance that keeps them anchored to the water. A tadpole changes from a gill-breathing, legless herbivore with fins and a two-chambered heart into a lung-breathing, four legged-carnivore with legs and a three-chambered heart.
CIRCULATORY SYSTEM
Closed circulatory system. This circulatory system consists of a double loop. The first loop moves oxygen-poor blood from the heart to pick up oxygen in the lungs and in the skin and then moves the oxygen-filled blood back to the heart. In the second loop, blood filled with oxygen moves from the heart through vessels to the body, where the oxygen diffuses into cells. The heart is 3-chambered with two atria (right atrium receives deoxygenated blood from body; left atrium receives oxygenated blood from the lungs) and one ventricle, which remains undivided.