Concept:Some animals lack red blood cells; their respiratory pigment is dissolved directly in the plasma instead of being packed inside cells.Explanation:Earthworms have hemoglobin dissolved in their blood, but they do not have red blood cells.Snakes and peacocks are vertebrates that have red blood cells containing hemoglobin.Therefore, among the given options, only earthworm is an animal without red blood cells.Answer:Option A: earthworm