Tiny, wide-eyed and helpless, there's something adorable about baby turtles. In fact, so small are the newborn hatchlings that they can comfortably sit in the palm of your hand as they gaze up at the world around themselves. Indeed, many species of turtles are just as vulnerable as they look, and are coming dangerously close to the precipice of extinction - the very real risk that they face from their natural predators, as well as from mankind, illustrated by the ease with which they can be picked up to be admired.

Another reason for the infants' defenselessness is that they have no one to look after them or to defend them. When turtles are ready to lay their eggs, they bury them in mud or sand and leave them to incubate themselves. On hatching the babies, which can number up to a dozen, wriggle to the surface and head towards water - but there are no known species of turtle in which the mothers care for their young, instead leaving their children to fend for themselves against the wild.

In some species of turtle the gender of the offspring is determined by the temperature at which the eggs are incubated - a higher temperature resulting in the birth of a female, while a lower temperature results in the birth of a male.

While the word 'turtle' tends to be used as an umbrella term to describe all members of the order Testudines, it is, perhaps confusingly, also common for some of its members to be referred to by other names, depending on their habitat. 'Tortoise' is internationally used for most land dwelling species, but in British English, though less so in US and Australian English, a distinction is made between turtles living in fresh water and turtles living in sea water, respectively calling them 'terrapins' and 'sea turtles'.

On the Marshall Islands baby sea turtles are so numerous that the locals keep them as pets, eat their eggs and even raise them for food. The eggs can be easily located on the dry beaches of the islands by locating softer patches of sand, where the turtles have buried their eggs. Failing that, the newborn babies can be easily plucked out of the water as they struggle against the tides. Fed on a diet of bread, fish and squid the animals change hands for as little as 25 cents. While some of the infant pets are released into the ocean on reaching maturity, it is questionnable whether they will be able to cope in the wild. The turtle illustrated above has recently hatched and still has its 'umbilical cord' from its egg.

The Diamondback turtle, or terrapin (shown above) is native to the brackish coastal swamps of the south eastern United States, and it is from there that terrapins take their name, from the Algonquian word torope. Living on a diet of mollusks and small fish, it takes males 2 to 3 years to reach maturity, growing to 12cm (4.5in), while females take around 4 years longer and grow 6cm (2in) larger. Pictured below is a map turtle.

The earliest known turtles lived 215 million years ago. Their present day descendants are thought to be able to live as long as 250 years. Researchers have recently discovered that, extraordinarily, turtle's organs do not seem to age, neither breaking down nor becoming less efficient with time, meaning that the liver, lungs and kidneys of a 100-year old turtle would be no different from those of one of the infants illustrated here, on reaching adulthood.

The turtle illustrated below is a bog turtle (Glyptemys muhlenbergii), recognizable by its distinctive yellow 'ears'. As it will only grow 10cm (4in) long, it is much closer to adulthood than many of the other turtles here. First discovered in Pennsylvania, the bog turtle is native to North America but is now an endangered species.

The two loggerhead turtles (Caretta caretta) shown below were photographed at Mon Repos beach in Bundaburg, Queensland, Australia. Loggerheads can be found in the Atlantic, Pacific and Indian oceans and in the Mediterranean. They come to sexual maturity from the age of 17 and live between 45 and 67 years - rather like human beings.

While turtles are commonly cold blooded, leatherback sea turtles (Dermochelys coriacea) have significantly higher body temperatures than the water they swim in, due to their higher metabolic rates. Leatherbacks are amongst the largest species of turtle and can eventually grow to be nearly 2m (6.6 ft) across, weighing nearly a metric tonne (2,000 lb). The one shown below was photographed at the Gumbo Limbo Environmental Complex in Florida.

Below is a snapping turtle, of the family Chelydridae. These turtles are known for their rugged, muscular build, their sharp beak, and, like many aquatic turtles, the placing of their eyes on the top of their head.