By Stacey Venzel
Unlike hermit crabs who rent multiple shells in a lifetime from other mollusks, turtles never switch shells. This is because the shell is part of their body, growing with the turtle as it ages.
The shell of Testudines is unique among reptiles and other animals, both in its mere existence and the general configuration. Even if it could, a turtle would not want to leave its shell behind considering the amount of protection it offers most species.
SHELL FOR LIFE
Muscles, cartilage, and bone are connected to the shell, preventing the turtle from even being able to move from one shell to another. Walking away from their shell would be akin to a car driving down the street without its windows, doors, and frame or a bird flying through the air without its spine and ribs.
Turtle shells are made up of two conjoined parts, the carapace on top and the plastron on the bottom. The scales on a shell are called scutes. Most turtles have 13 scutes on the top of the carapace and 10 to 13 scutes on each side. Turtles with more pliable shells, including the leatherback sea turtle and softshell and pig-nosed turtles, do not have scutes but rather leathery skin.
Scutes are made of keratin, the same protein that makes up your skin and fingernails. Similar to how nerves under your fingernails allow you to feel something scraping them, a turtle’s shell can feel touch. This means they can feel a good back scratch but also pain from shell trauma, like the many tortoises that get hit by cars.
ROLE OF THE SHELL
Acting as a shield housing all their organs, the shell protects turtles from predators. Generally, the thickness and sturdiness of a shell indicates the level of predation or competition for a species. Sea turtles, sliders, and cooters need protection against the strong jaws of sharks and alligators. The spiny turtle has spikes that ward off snakes. Theories suggest the ornate box turtle evolved a thick shell to protect against stampedes of bison that foraged in the same area. Tucking into their shell can also help forest-dwelling turtles, like the brown wood turtle, survive wildfires.
Stephen Divers, Doug Mader, Current Therapy in Reptile Medicine & Surgery, (St. Louis, Elsevier Saunders, 2014), 322-323.
Karen Eckert, David Gulko, Sea Turtles: An Ecological Guide (Honolulu, Mutual Publishing, 2004), 49.
Carl J Franklin, Turtles: An Extraordinary Natural History 245 Million Years in the Making (St. Paul, Voyageur Press, 2007), 15, 17-18.
Whit Gibbons, Judy Greene, Turtle: The Animal Answer Guide (Baltimore, The John Hopkins University Press, 2009), 19-20.
Jeanette Wyneken, The Anatomy of Sea Turtles (Miami, US Dept of Commerce NOAA Technical Memorandum NMFS-SEFSC-470, 2001), 1-2, 4, 45-50.