Plastrons and the Physical Gill:
Respiration of Aquatic Arthropods
Respiration can be defined as "the gaseous exchange of oxygen and carbon dioxide" (Breene III "Respiration in Spiders"). The job of the respiratory system, then, is to transport sufficient oxygen to the body's cells and remove carbon dioxide from the body (Meyer 2006). This website explores how insects and spiders that spend some to all of their life underwater are able to carry on the process of respiration while submerged in aerated water.
Insect respiration and spider respiration are different processes. The insect respiration system is separate from its circulatory system. This is possible because its tracheal system, which delivers oxygen-containing air throughout the insect's body through a network of tubes, are in close enough contact with the insect's tissues that the presence of an oxygen transporter is not necessary (Breene III "Respiration in Spiders). Spiracles are openings in the exoskeleton of the insect, through which the intake of air is possible. In insects, the spiracles can be found along the side of the thorax and abdomen (Meyer 2006).
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Abdomen of an insect without wing covers- spiracles can be observed along the right side (source: Miall, L.C.)
Muscles that can control valves in the spiracles regulate the movement of air into and out of these openings. Once the air passes through a spiracle, it then is transported through the tracheal system (Meyer 2006). For the purposes of examining aquatic respiration of insects, it is the movement of oxygen into the spiracles that is of the most concern because insects to not have the ability to exchange gas directly with the water. Gas exchange can only occur through contact with the air. Thus, in order to respire while under water, some insects have evolved the use of either a physical gill or plastron breathing, which provide the insect with a bubble of air surrounding the segment of their exoskeleton containing spiracles.
The respiratory system of spiders differs slightly from that of insects. Rather than having separate circulatory and respiratory systems such as in insects, spiders require blood (hemolymph) for respiration. There are at least five possible respiratory systems in spiders, but in each system the tracheal tubes transport air to hemocyanin pigments which transports oxygen to the cells and brings carbon dioxide back to the tracheal tubes to be expelled. However, although the transport of oxygen within the body of insects and spiders differs, spiders, like insects, also contain spiracles on their exoskeleton through which air is input. Spiracles on spiders can be found on the ventral side of the abdomen (Breene III "Respiration in Spiders").
Diagram of ventral features of spiders (Pardosa sp.) (Image credit: adapted from an image by Patrick Edwin Moran)
Thus, both aquatic spiders and aquatic insects need a method of maintaining a supply of oxygen-containing air surrounding their spiracles in order for respiration to continue under water. Physical gills, a temporary air bubble that must be replenished regularly, and plastrons, non-compressible air bubbles that do not decrease in volume over time, are two methods by which this is possible. Learn more about how they function here.
|How do physical gills and plastrons work?|
|How is research of this topic performed?|
|Benefits and Limitations|
|Biomimicry: The plastron’s Contribution to Technology|
|Other Superhydrophobic Surfaces in Biology|
|Some Aquatic Insects and Spiders|
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This website was created as a part of a class project in the Animal Physiology Class at Davidson College.