The turtle’s always been inclined
to live within his shell.
But why he cares to be confined,
the turtle does not tell.
The turtle’s always satisfied
to slowly creep and crawl,
And never wanders far outside
his living room or hall.
So if you wish to visit him
in his domestic dome,
Just knock politely on his shell —
you’ll find the turtle home.
Steele Creek Park in Bristol, TN, was the site of this week’s nature study class. Hoping to surprise some turtles basking on a large fallen tree in the shallows, we began our time together by creeping quietly down to the lake. Our stealth was rewarded by finding several specimens of differing size bathing in the afternoon sun. After sharing some extremely corny “turtle jokes” (Why did the turtle cross the road? To get to the Shell station. What do you get when you cross a turtle with a porcupine? A slow poke.) we entered the Nature Center where several species of turtles are kept in huge tanks. After Jeremy Stout, manager of the Nature Center, fed the huge snapping turtle so we could watch it sneak up on its prey and POUNCE, the students each chose which species they’d most like to see “up close and personal” and I asked some questions to start their observations.
— Describe the turtle’s skin (what little you can see outside the shell). (Reptiles have dry, scaly skin (herpetology is the study of scaly things) and amphibians have smooth skin.)
— Compare the upper (carapace) shell with the lower (plastron). How are they shaped differently? (Most turtles have a curved carapace but in some species it’s flat.) Are the shells of different colors? Why might the carapace be darker and the plastron be lighter? (For purposes of camouflage. Predators or prey looking UP from the bottom of the body of water would see a light color like the sky, while those looking DOWN from above would see a darker color like the substrate.)
— Make a quick sketch of the upper and lower shell showing the shape of the plates that compose them. Where are the two grown together? (The carapace is grown fast to the backbone of the animal, and plastron to the breastbone.)
— Describe the turtle’s eyes. Does the turtle have eyelids? (Turtles’ eyes have nictitating membranes (“nictare” = Latin “to blink”) — a transparent or translucent third eyelid that can be drawn across the eye for protection and to moisten it while maintaining visibility. The turtle’s nictitating membrane comes up from below and completely covers the eye.)
— Do turtles have ears? (Turtles have 3 ears — 2 located on the sides of their head (small holes) and one on their nose. Turtles have “inner ear” mechanisms that other animals have. The outer ear gathers vibrations which makes the sound louder. While turtles can’t hear airborne sounds, they do sense and interpret vibrations within their environments. Meanwhile, the organs in a turtle’s ears do help them feel changes in water pressure that can warn them of the presence of predators.)
— Describe the turtle’s mouth. Are there any teeth? How does the turtle bite off its food? (The turtle has no teeth but strong, cutting jaws called a “beak.”) Describe the movement of the turtle’s throat. What is the cause of this constant pulsation? (The turtle is swallowing air for breathing.)
— Describe the shape of the legs. How many claws on the front feet? (5) On the back? (4) Are any of the toes webbed? On which feet are the webbed toes? Why should they be webbed? (To enable the turtle to swim faster.) Describe the way a turtle swims. Which feet do you think the turtle uses as oars? (Those which are webbed.)
I shared with the students that like all reptiles and amphibians, turtles are ectothermic (cold-blooded) animals, relying on their environment for warmth. Unlike some animals which hibernate (one lengthy period of inactivity) in winter, cold-blooded animals brumate (periodic awakening and temporary resumption of activity and feeding). In winter, water turtles may bury themselves in the ooze at the bottom of ponds and streams. Land turtles dig themselves into the earth for several short winter naps.
THE TURTLE SHELL
The shell is composed of hard, bone plates covered by scutes. The scutes are made of keratin, the primary substance in hair, nails and hooves. Pigments may form intricate designs and bright patterns in some species. Although the scutes form the familiar outer layer of the shell, it is the bony layer underneath which actually provides the shape, support and protective qualities of the turtle shell.
The vertebrae of the neck and tail are small, allowing for a high degree of flexibility, while the vertebrae of the central portion of the vertebral column are enormously elongated and inflexible, fused with the bony layer of the shell, acting as a support for the carapace. If the outer keratin is breached by infection or injury, the turtle can lose its protection and infection can proceed into the bony layer and the body cavity, threatening the turtle’s life.