    – –     Figure 42.2 Circular canal Mouth Radial canals 5 cm (a) The moon jelly Aurelia, a cnidarian (b) The planarian Dugesia, a flatworm Gastrovascular cavity Mouth Pharynx 2 mm  Body size and shape- to keep cells in contact with their enviromentCirculatory System- moves fluid between each cell’s surroundings and the environmentExchange gasesAbsorb nutrientsDispose of waste    Figure 42.3 (a) An open circulatory system Heart Hemolymph in sinuses surrounding organs Pores Tubular heart Dorsal vessel (main heart) Auxiliary hearts Small branch vessels in each organ Ventral vessels Blood Interstitial fluid Heart (b) A closed circulatory system Circulatory fluidInterconnecting vesslesMuscular pump          Receives BloodPumps bloodIn a house :- Atrium: entry way to a house-vents: pump out airFigure 42.4 (a) Single circulation (b) Double circulation Artery Heart: Atrium (A) Ventricle (V) Vein Gill capillaries Body capillaries Key Oxygen-rich blood Oxygen-poor blood Systemic circuit Systemic capillaries Right Left A A V V Lung capillaries Pulmonary circuit Figure 42.5 Amphibians Reptiles (Except Birds) Pulmocutaneous circuit Pulmonary circuit Lung and skin capillaries Atrium (A) Atrium (A) Left Right Ventricle (V) Systemic capillaries Systemic circuit Systemic circuit Systemic circuit Systemic capillaries Incomplete septum Incomplete septum Left systemic aorta Left Right Right systemic aorta A A V V Lung capillaries Lung capillaries Pulmonary circuit A A V V Left Right Systemic capillaries Key Oxygen-rich blood Oxygen-poor blood Mammals and Birds