The plastron is a series of bony plates on the underside of a turtle or tortoise shell that protect the belly. It allows the turtle to withdraw its head, tail, and four legs into its shell. Turtles are reptiles that may live on land, or near freshwater or saltwater. Land dwelling turtles are often referred to as tortoises.
Turtle shells are made of fused bones. The top part of the shell is called the carapace, which is dome shaped on land turtles. Aquatic turtles have flatter top shells to aid them in swimming. One of plastron’s primary definitions is that of a metal breastplate worn under a suit of body armor. It also refers to the protective vest worn by fencers. It is derived from the Italian word piastrone, meaning metal sheets or a breastplate.
Six symmetric pairs of scutes extend from a central seam on the plastron. The design somewhat resembles a fish skeleton. The scutes are covered with keratin, the same material that makes up horses hooves and fingernails. Scutes help form the plates into a hinge, allowing the turtle to pull the top and bottom shells together over its body when in danger. The shell acts as a kind of armor until the threat has passed.
Dysecdysis is a shell disease caused when scutes are retained and not properly shed. Turtles may also suffer from metabolic bone diseases that can result in shell deformities. Turtle shells can also be become ulcerated, resulting in sickness.
The turtle species is estimated to be over 215 million years old. Powdered turtle plastron has long been used in China as a remedy for kidney and liver problems and to strengthen bones. Natural medicine practitioners in other countries advocate it as a restorative for people suffering exhaustion.
Both the tortoise and the turtle have played important roles in the mythology and spiritual life of the world’s cultures. The ancient Greeks believed that the turtle was a favored creature of the gods. It was thought to be sacred to Aphrodite and Hermes, deities associated with sexuality.
Turtle shells were used as oracle bones by the Chinese during the Shang dynasty, about 1300 B.C. By tracing the fissures on the shells and then heating or cracking them, it was believed that the outcome of particular undertakings could be divined. Some of the earliest Chinese writings have been discovered by archeologists on the plastron of turtle shells.
In Native American culture, the turtle is a part of creation myth. The Lakota Indians did not kill or eat turtles because they are a symbol of life. The turtle appears in Native American artwork and on medicine bags and amulets. It was considered to have special powers because the number of scales on its shell corresponded to the 12 days between moon cycles.