Whether or not a turtle can hide in its shell or not is dependent upon the particular species, its lifestyle and its habitat. Sea turtles for example have a light streamlined shell that is covered with leathery skin. Freshwater turtles have a hard shell but in some species if they are smaller they may be too small to protect their entire body. Land turtles and tortoises are equipped with hard, domed shells, which they rely on largely for protection from predators.
Many turtles as well as tortoises are indeed able to pull in all four legs and their heads to hide in their shell. Their shells protect them from predators and also help them feel safe if they were feeling threatened or in danger before retreating into their shell. When a turtle pulls its head into its shell for protection its neck either folds to the side or into a vertical S shape, and the skin of the neck also bunches up. Which is where the term turtleneck came from.
With many species of turtles the outer skin of the legs is hard, rough and in some tortoises is also armored giving the turtle more protection. Aquatic turtles usually dive into water when they are feeling threatened. Their skin is much softer and equipped with fewer protective scutes. For some species of turtles that lack a good hard shell for armor from predators, they use their legs or the claws between their toes as means of defending themselves.
Some turtles are not only able to hide in their shells, but also able to close their shell, which provides them with additional protection against predators. There is a hinge across the bottom of these particular species of turtle’s shell known as the plastron. This hinge can close the front and the rear and keeps the turtle well concealed inside the shell.
The muscles that hold a turtle’s shell are very tough and after the hinge (plastron) is shut there is no way to open it back up without causing harm to the turtle. There are certain species of tortoises that are also able to close their shells. Tortoises such as the hinge-back tortoise have a hinge across the top of their top shell known as the carapace and are able to close in the back legs as well for protection.
It is to the turtle’s advantage that they are able to hide in their shells, however even though their shells are made of bones they are still quite vulnerable. Predators are actually even able to chew and break open the shell. A larger bird of prey can pick up a small turtle and drop it on rocks below to break the turtle’s shell like a person would crack an egg. A turtle’s shell can also protect it from a small and fast moving wildfire, however larger and hotter fires will most definitely kill a turtle or tortoise that is trapped in it. Domestic pets such as dogs have been known to make turtles into chew toys, which usually ends in disaster for both parties as it can kill or severely harm the turtle and also poison the dog as many species of turtle’s skin is toxic if ingested.