Integumentary appendages of chelonians.

The head and neck of four families of turtles, the Chelydridae, Kinosternidae, Pelomedusidae, and Chelidae, possess a diverse assemblage of skin appendages. Appendages are termed barbels when they occur in the gular region and tubercles when they occur other places. The appendages consist of protrusions of the dermis and epidermis and are devoid of such specializations as taste buds or neuromasts. They lack skeletal tissue, muscle, or erectile tissue. Methylene blue and silver staining techniques reveal a high density of nerves. The occurrence and morphology of barbels and tubercles suggest that they function as mechanoreceptors. Skin appendages are most elaborate in carnivorous species and reach maximum development in two distantly related convergent species: Macroclemys temmincki (Chelydridae) and Chelus fimbriatus (Chelidae). Skin appendages also help provide camouflage and disruptive effects on the head. The increase in surface area produced by the appendages may be important in aquatic respiratory gas exchange in some species within the Kinosternidae.