plastron

Plastron is a term used in biology to refer to two distinct concepts.

In turtles and tortoises, the plastron is the ventral part of the shell, forming the underside shield that pairs with the dorsal carapace. It is typically composed of flattened bones that may be fused or sutured and is usually covered by keratinous scutes. In many species the plastron includes a hinge, allowing the front and rear sections to move relative to one another. This flexibility aids in retracting the limbs and head for protection. Plastron shape and the arrangement of its scutes can aid in species identification and may reflect developmental or sexual variation in some groups.

In aquatic insects and some other invertebrates, the term plastron describes a specialized surface that traps a thin film of air against the body when submerged. This physical air layer, maintained by a hydrophobic microstructure of the cuticle, permits gas exchange with the surrounding water and reduces the need to ascend for air. Plastrons can be continuous or segmented and are a key adaptation for prolonged underwater life in certain larvae, nymphs, and other aquatic organisms.

The two uses of plastron are unrelated in function and anatomy: one is a shield-like bone structure forming part of a turtle’s shell, the other is a cuticular surface feature enabling underwater respiration in various aquatic animals.