Arachnid respiration is primarily through which structures?

• A. Gills
• B. Trachea or book lungs
• C. Lungs
• D. Skin diffusion

Answer: (B)

Arthropod respiration in arachnids relies on internal structures that are well-suited for living on land: a tracheal system and, in many spiders, book lungs. The tracheal system consists of air-filled tubes (tracheae) that deliver oxygen directly to body tissues through openings called spiracles. Book lungs are internal, leaf-like membranes that provide a large surface area for gas exchange. Gills are used by aquatic relatives, and true lungs of vertebrates aren’t the typical feature seen in arachnids. Diffusion across the skin isn’t the primary mechanism because the outer surface is usually dry and doesn’t provide enough surface area or a moist environment for efficient gas exchange. So the main structures used for respiration in arachnids are the tracheae or book lungs.