The word "tortoise" means different things to different people. In the UK, it refers to any member of the shelled reptile family inhabiting dry land. Marine species are called turtles, and freshwater species are called terrapins. In the USA, all shelled reptiles are referred to as turtles, whether aquatic or not. In Australia, all but one of the native turtles are referred to as tortoises.
Turtles As Pets
Turtles have been kept as pets for hundreds of years. Massive raids on wild species brought many of the them to the brink of extinction. Many die in captivity due to poor conditions and lack of knowledge about their needs. Certain species of tortoises are included in the Convention on the International Trade of Endangered Species (CITES) lists the species that are threatened with extinction in their natural habitat. Tortoises make excellent pets. Different species need specific housing and feeding requirements.
There are many popular misconceptions about turtle and tortoise shells. They are, in fact, made of living tissue. The main part of the shell is bone, complete with its own narrow cavity, covered in a layer of horny skin that provides the coloration and patterns seen on the individual species. The shell is divided into a number of regions, al of which help to identify each species, and individuals within each species.
The upper shell is the carapace, and the lower or the underside of the shell is the plastron. The carapace is attached to the plastron between the fron and rear limbs by what are known as the pillars. Finally, the individual carapace and plastron are divided into individual segments called scutes. These scutes are given names according to their position on the body of a turtle. Trauma to the shell can result in serious infections.
Turtles can also feel pain through injuries to their shells, and this has particular significance when restraining them. They should never be tethered to a rope or chain via a hole drilled in their shell, as was a practice a number of years ago.
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Other animals move their ribcage up and down to moe air in and out of their lungs, but turtles cannot do this. They use their legs, neck and limbs as bellows, moving them in and out of the shell, even during the sleep, moving in and out of the lungs.
A turtle's lungs sit in the upper part of the shell, on top of the liver and digestive system. They do not have a true diaphragm to separate these functions so, if a turtle is unfortunate enough to fall on its back, its lungs become squashed under the weight of its gut. If the turtle is not righted, this can lead to suffocating.
Turtles produce a different type of urine from mammals. In mammals, urine waste, termed urea, is soluble. In retiles and birds, much of the urea is not soluble. This is a white, ceam or yellow part of the feces that turtle passes. It is often accompanied by some more conventional watery urine.
Turtles are "cold-blooded", or ectothermic, which means that they rely on their environment to provide their body heat.