Which is an Animal without red blood cells

Step 1: Analyze the question We need the animal that has no red blood cells (erythrocytes) in its blood.

Step 2: Explain the concept Red blood cells carry oxygen using haemoglobin. Vertebrates (fish, amphibians, reptiles, birds, mammals) all have red blood cells. Many invertebrates do not have them. Their blood or body fluid either carries dissolved pigment in the plasma or has other cell types.

The earthworm is an annelid. It has a closed circulatory system, but its haemoglobin is dissolved in the plasma, not packed inside red blood cells. So it has no red blood cells.

Step 3: Check each option

• A. Frog: an amphibian, a vertebrate. It has nucleated red blood cells.
• B. Earthworm: an invertebrate. Its haemoglobin is dissolved in the plasma, and it has no red blood cells.
• C. Snake: a reptile, a vertebrate. It has nucleated red blood cells.
• D. Peacock: a bird, a vertebrate. It has nucleated red blood cells.

Step 4: Answer The earthworm is the only animal listed without red blood cells.

Tip: In "which animal lacks red blood cells" questions, look for the invertebrate among the options (earthworm, insect, snail). Every vertebrate has red blood cells. Insects also lack them, since their blood (haemolymph) does not carry oxygen.