by Kathy Rusniak

Created on: May 04, 2009

Tortoise versus Turtle

Forget the tortoise and the hare. How about the tortoise and the turtle and the terrapin? All are known for carrying their homes on their backs, being cold-blooded and laying eggs. But what else do we know about these exotic and globally pervasive animals?

The word turtle is used both generically and specifically, and so depending on the context of the usage can mean either all shelled reptiles (living on land and in water) or may indicate those animals living in the water only. The meaning can also be slightly different depending on the region of the country or world a person if from. In the U.S. it is common to call all water, river and delta dwelling varieties turtle', with the exception of one particular species referred to as terrapin, while someone from abroad may refer to ocean varieties only as turtle' and call all those fresh and brackish water varieties terrapin. In the U.S., the ocean dwelling turtles are usually specifically referred to as sea turtles'. Regardless of these distinctions within the turtle group, most people agree that a tortoise is the land dwelling form of this shelled reptile.

To avoid too much confusion, scientists usually refer to the whole group of shelled reptiles as chelons', and then use the term turtles' for the water inhabiting varieties. Here, turtle will also be used to refer to all water dwelling types.

All turtles, terrapins and tortoises have shells of some sort on their backs that they carry around with them sort of like a mobile home. The shell is basically an extension of the turtles skeletal structure which forms an outer covering sometimes referred to as an exoskeleton, which is made of keratin and forms large, scale-like structures called scutes.
This may sound familiar if you've ever read about human physiology or entomology and learned that human hair and nails and the exoskeletons of insects are all made out of the same substance - keratin.
But the shells of turtles/terrapins and tortoises are usually much stronger and thicker. Of course, not all turtle species have the exact same shell design.
Some turtles actually have a relatively softer and more flexible shell for bending, maneuvering and squeezing under things like rocks. And some species have a smooth, leathery covering of skin on the outer surface of the shell.

Although the shell is often called the turtle or tortoises home', it is more true to say this is their main line of defense or protection against predation. Most turtles and tortoises

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