The diving bell and the spider: the physical gill of Argyroneta aquatica

Argyroneta aquatica is a unique air-breathing spider that lives virtually its entire life under freshwater. It creates a dome-shaped web between aquatic plants and fills the diving bell with air carried from the surface. The bell can take up dissolved O-2 from the water, acting as a 'physical gill'. By measuring bell volume and O-2 partial pressure (P-O2) with tiny O-2-sensitive optodes, this study showed that the spiders produce physical gills capable of satisfying at least their resting requirements for O-2 under the most extreme conditions of warm stagnant water. Larger spiders produced larger bells of higher O-2 conductance (G(O2)). G(O2) depended on surface area only; effective boundary layer thickness was constant. Bells, with and without spiders, were used as respirometers by measuring G(O2) and the rate of change in P-O2. Metabolic rates were also measured with flow-through respirometry. The water-air P-O2 difference was generally less than 10. kPa, and spiders voluntarily tolerated low internal P-O2 approximately 1-4. kPa before renewal with air from the surface. The low P-O2 in the bell enhanced N-2 loss from the bell, but spiders could remain inside for more than a day without renewal. Spiders appeared to enlarge the bells in response to higher O-2 demands and lower aquatic P-O2.