Most water turtles have relatively flat shells naturally designed for fast swimming and diving.
What makes turtles different from all other reptiles is their shell. Generally the shell is hard and protects the turtle from its predators; however, certain species are soft-shelled. Unlike crabs, turtles cannot leave the shell as it partially consists of their backbone and ribs, making the turtle permanently attached to its protective covering.
In most species, the shell is made up of bone segments covered with scutes. Scutes are horny scales which make the shell stronger by covering up seams between bone plates. However, soft-shelled turtles and leatherback turtles lack scutes – their shells are covered with leathery skin. Most water turtles have relatively flat shells naturally designed for fast swimming and diving.
The shell consists of the top part – carapace, and the bottom part – plastron. The two are joined on the sides by bridges. Males tend to have a concave plastron which makes it easier for them to place themselves on top of their mate. Females sometimes have a convex plastron, which gives more space for eggs.
While most terrestrial turtles have short heavy legs, water turtles usually have longer legs with webbed feet. This makes them good swimmers, yet gives sufficient mobility on land as well. Their claws are generally quite long, which helps them dig and crawl onto rocks or wood when they want to bask. Males tend to have especially long front claws that they use to grab onto the female while mating. These long claws also appear to be involved in courtship.
Sea turtles, as well as certain species of freshwater turtles, have flippers instead of feet. These turtles spend most of their time in the water – they are great swimmers, but have a hard time getting around on land.
Most water turtles are able to retract their limbs into the shell.
Head and Neck
Unlike sea turtles, most freshwater turtles are able to fold their neck and hide their head in the shell. The arch-necked turtles (Cryptodira) can withdraw their neck and head into the shell, whereas side-necked turtles (Pleurodira) fold their neck to the side and hide it along their body.
Turtles don’t have teeth. Instead they have strong toothless jaws and sharp-edged beaks. They use the hard edges of their jaws to catch prey and cut through food. Unlike many other reptiles, turtles are unable to hunt by means of sticking out their tongue. Due to the fact that their tongue is fixed, water turtles are only able to swallow in the water.
Turtles do not have external ears, but they do hear. Although they don’t hear sounds as clearly as animals with outer ears do, they can feel vibrations and interpret them at a level sufficient for their needs.
The nose and eyes of most aquatic turtles are located closer to the top of the head so they are able to keep most of their head underwater while the nostrils and eyes stay outside. This often helps them hide from their predators. The vision of water turtles varies from species to species. A lot of them have sharp vision and are able to distinguish colors. However, many turtles can only see sharply while under the water and become short-sighted when on land.
The skin of most turtles is similar to that of other reptiles. Most of their skin is protected by small scales. Certain species of water turtles are able to take in oxygen from the water through skin. As they grow, turtles shed their skin gradually. They don’t shed all their skin at once like snakes do, but instead their skin comes off in small thin bits which can be seen in the water of the tank if the turtle is kept in captivity. Excessive shedding can be a sign of disease. It also occurs in pet turtles if they are overfed or the water in the tank is too warm.
Tail and Cloaca
The tails of most water turtles are rather small, with the male’s tail being a bit longer and thicker than the female’s. However, certain species have long scaly tails that they use to support their weight while climbing.
The cloaca is the opening that the urinary, digestive and reproductive tracts share. In females the cloaca is usually located closer to the shell, while in males it is closer to the tip of the tail. Turtles of certain species are also able to absorb oxygen through papillae in their cloaca. This ability is usually used when the turtle needs to stay underwater for a long period of time, such as during hibernation.