If you were a fan of 'Mutant Ninja Turtles' like me, you already know what they look like. Though mutant turtles are not available as they are busy fighting the bad guys, you could choose from many other species. Turtles are reptiles and one of the oldest creatures that evolved on Earth, over 215 million years ago. There are about 300 species on the planet today and most of them are endangered. They can be classified into land turtles (called tortoises), sea turtles (saltwater species), and Terrapins (living in brackish water). They are cold-blooded (Ectothermic) creatures, that is, their body temperature is same as their surroundings, unlike mammals like us, with a fixed body temperature. They lay eggs on land and not underwater. There are many different types of turtles. Small terrestrial and freshwater species are popular. Among them, the most popular are Red-eared Sliders (a.k.a. Red-eared Terrapin) and Russian tortoises. It is illegal in any state, in the United States of America to sell species, which are smaller than 4 inches in length. This restriction was put due to the spread of Salmonella, through contact with these organisms. The Most Popular Species These are the two popular species, that you can find in your neighborhood pet shops. Once you buy a turtle, it can be a companion for many years to come as they have a long lifespan. Russian Tortoise Also known as Horsefield's Tortoise or Central Asian Tortoise, it is probably the only Russian thing , popular in USA, other than Anna Kournikova. They are small in size and grow to about 15-20 cm in length. Females are larger than males in size. One way to distinguish a male Russian tortoise from a female, other than the size difference, is observing their tail. Males have long tails, while females have shorter ones. Females have bony external plates called scutes on their shell, while males do not. So in general, female Russian turtles are more formidable than males. Their body color is yellow and brown, while their shell color patterns may range from ruddy brown to black patches, on a yellow background. They hibernate or rather brumate, during winter and mostly sleep during summer, when the heat is high. Their natural habitat is generally dry, with sparse vegetation. They simply love burrowing and are herbivores. They like eating tomatoes, zucchini, lettuce, and dandelions are their favorite food. They also eat fruits. This species has the rare honor of being the first turtle in space, thanks to a Soviet mission launched in 1968. Red-Eared Slider The red-eared slider, known commonly as Red-eared Terrapin, in the UK, is a popular choice. It is a semi-aquatic species and is native to southern United States. It has become a popular pet in United States and all over the developed world due to pet trade. It can be identified by the distinct red mark situated around its ear and which they are named after. These turtles require an aquatic habitat and are excellent swimmers. They are shy creatures who lay their eggs on land and prefer to eat their food in water. They grow up to 25-30 cm in size. Their bodies are green in color, with fine irregular yellow lines. The shell is dark green with patches on the top and yellow on the bottom. They are aquatic and omnivores. They eat fish and other small aquatic fauna and also hibernate in winter. Turtles as pets are excellent companions. You must care for them, as they are very vulnerable creatures.