Plastrons A plastron is a type of structural adaptation occurring among some aquatic arthropods (primarily insects), a form of inorganic gill which holds a thin film of atmospheric oxygen in an area with small openings called spiracles that connect to the tracheal system. The plastron typically consists of dense patches of hydrophobic setae on the body, which prevent water entry into the spiracles, but may also involve scales or microscopic ridges projecting from the cuticle. The physical properties of the interface between the trapped air film and surrounding water allow gas exchange through the spiracles, almost as if the insect were in atmospheric air. Carbon dioxide diffuses into the surrounding water due to its high solubility, while oxygen diffuses into the film as the concentration within the film has been reduced by respiration, and nitrogen also diffuses out as its tension has been increased. Oxygen diffuses into the air film at a higher rate than nitrogen diffuses out. However, water surrounding the insect can become oxygen-depleted if there is no water movement, so many such insects in still water actively direct a flow of water over their bodies.
plastrons a plastron is a type of structural adaptation occurring among some aquatic arthropods (primarily insects) a form of inorganic gill which holds a thin film of atmospheric oxygen in an area with small openings called spiracles that connect to the tracheal system the plastron typically consists of dense patches of hydrophobic setae on the body which prevent water entry into the spiracles but may also involve scales or microscopic ridges projecting from the cuticle the physical properties of the interface between the trapped air film and surrounding water allow gas exchange through the spiracles almost as if the insect were in atmospheric air carbon dioxide diffuses into the surrounding water due to its high solubility while oxygen diffuses into the film as the concentration within the film has been reduced by respiration and nitrogen also diffuses out as its tension has been increased oxygen diffuses into the air film at a higher rate than nitrogen diffuses out however water surrounding the insect can become oxygen-depleted if there is no water movement so many such insects in still water actively direct a flow of water over their bodies