Spleen receives oxygenated blood only. Lungs and gills receive deoxygenated blood for the oxygenation. The liver also receives deoxygenated blood through the hepatic portal system. So, the correct answer is option D.

Answer:
The correct answer is option D, the spleen.

Explanation:
- The spleen is an organ found in vertebrates, including humans. It is located in the upper left part of the abdomen, behind the stomach.
- The spleen is involved in the immune system and functions as a blood filter, removing old or damaged red blood cells and platelets from circulation.
- However, the spleen does not receive oxygenated blood directly. It receives blood from the splenic artery, which is a branch of the celiac artery.
- The splenic artery carries oxygenated blood to the spleen, but the spleen itself does not participate in the oxygenation of blood.
- The spleen's main function is to remove old or damaged blood cells and platelets, not to receive oxygenated blood.
- The oxygenation of blood primarily occurs in the lungs, where oxygen is taken up and carbon dioxide is released.
- The lungs receive deoxygenated blood from the right side of the heart through the pulmonary arteries, and oxygenated blood is returned to the left side of the heart through the pulmonary veins.
- The gills, on the other hand, are respiratory organs found in aquatic animals like fish. They are responsible for extracting oxygen from water.
- The liver is a vital organ involved in various metabolic processes, including detoxification, protein synthesis, and production of bile.
- While the liver receives blood from the hepatic artery and the hepatic portal vein, it does not exclusively receive oxygenated blood.

Therefore, the spleen is the only organ among the given options that does not receive oxygenated blood directly.