Exactly what is a clemmysian fold?
August 25, 2025
Globally, there are approximately 350 species of turtles with a wide variety of anatomic and physiologic differences, ranging from sea turtles with large and slender flippers adapted for propulsion during swimming, to snapping turtles that have extremely flexible necks for quickly catching prey.
In a recent study, Museum Chief Veterinarian Dr. Dan Dombrowski, North Carolina State University veterinary student-intern Meghan Chung and others describe for the first time an interesting structure on the neck of spotted turtles (Clemmys gutatta). How does it work? The structure is divided into two halves or folds, located on each side of the neck, that align to close over the retracted head of the turtle like a vertical “clamshell.”
“While performing a medical exam on a shy spotted turtle, I noticed this unusual fold of skin protecting the retracted head and neck,” Dombrowski said. “This structure did not look like anything I had ever seen on any other turtle species — and I have worked with lots of turtles. This is one of those situations where something really has been right in front of us for a long time, hiding in plain sight.”
Dombrowski, Chung and colleagues gathered images and tissue samples for this project using deceased fluid-preserved specimens from the Museum’s own herpetology collections as well as from collections at the Carnegie Museum of Natural History. They then worked with colleagues to examine and describe the microscopic structures in the tissue samples and collect data from live spotted turtles in the field.
While the structure’s function is currently unknown, Dombrowski and colleagues suspect it serves a protective role for the head and neck of the turtle, much like the hinged shell of some other turtles. And, based on the other species evaluated in this study, the structure appears to be unique to spotted turtles.
The Museum’s Research Curator of Herpetology Dr. Bryan Stuart suggested naming the structure the clemmysian fold, a nod to the scientific classification of spotted turtles as the only living species in the genus “Clemmys.”
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