Q. Which respiratory adaptations or organs do aquatic and terrestrial arthropods respectively present?

In crustaceans, typical aquatic beings, there are richly vascularized gills that permit gas exchange and make contact with water. In terrestrial insects the respiration is gases and tracheal flow inside small tubes that connect the animal external surface and ramify to cells and tissues without the participation of blood. In arachnids, besides the tracheal respiration, book lungs (thin folds resembling leaves in a book) may as well exist.