The excretory system of arachnids includes which of the following structures?

• A. Malpighian tubules
• B. Green glands
• C. Nephridia
• D. Kidney-like tissue

Answer: (A)

In arachnids, the main excretory structures are Malpighian tubules. These slender tubules pull waste products from the hemolymph and secrete them into the gut, where they mix with feces and are expelled. This arrangement supports efficient water conservation, which is crucial for terrestrial life, because wastes are often excreted as uric acid or urates rather than as a large, water-heavy urine. The tube system connects to the hindgut, allowing the animal to reclaim water and some ions before elimination. Green glands are found in crustaceans, not arachnids. Nephridia are typical of segmented worms, and a generic “kidney-like tissue” isn’t the discrete excretory organ arachnids use.