plastrons

Plastron is a term used in zoology to describe two distinct anatomical features in different animal groups. In turtles and tortoises, the plastron is the ventral portion of the shell. In some aquatic insects, the term refers to a specialized surface that enables underwater respiration by trapping a thin film of air against the body.

In turtles, the plastron constitutes the underside of the shell and is formed by several bones that fuse as the animal develops. It bears scutes and, together with the carapace, provides protection for the body. In some species, the plastron can be connected to the carapace by a hinge, allowing the shell to close more completely for defense. The shape, size, and pattern of the plastron vary among taxa and can be used in species identification and study of evolutionary relationships.

In aquatic insects, a plastron refers to a microstructured, air-retaining surface on the body that functions as a physical gill. The dense, hydrophobic hairs or cuticle trap a thin layer of air against the insect’s body, enabling gas exchange with the surrounding water while the insect remains submerged. This adaptation supports prolonged underwater respiration and can influence behavior such as diving and foraging. The effectiveness of a plastron can be affected by water quality, surface tension, and external disturbances.

Outside zoology, plastron has other meanings in different languages and contexts, but in biological usage it primarily covers these two senses: the ventral turtle shell component and the submerged respiratory surface seen in certain aquatic insects.