At first glance the turtle anatomy may appear to be simple, however, underneath of its shell turtle can be fairly complex.
- Head: foremost part of a tortoise which is attached to the trunk
- Neck: part of a tortoise between the head and the body
- Nuchal shell: hard plate that forms the shell of the tortoise close to the nape of the neck
- Vertebral shell: scale above the tortoises spinal column
- Costal shell: side scale
- Pygal shield: scale situated above the tail
- Tail: extension of the spinal column of a tortoise
- Nail: nail of a tortoise
- Hind leg: rearmost limb of the tortoise
- Marginal shell: each of the scales that form the edge of the tortoise’s shell
- Front leg: foremost limb of the tortoise
- Mandible: lower jaw
- Mouth: entrance to the digestive tract
- Nostril: entrance to the respiratory system
- Eye: sight organ of the tortoise
Turtle appearance can be easily identified by its shell. Shell plays a vital part in protection. Not much has changed in over 200 million years of evolution. Turtle shell form and function is still the same.
On the turtle’s side plastron and carapace are joined together with bony structures called bridges. The inner layer of the shell is made out of bones. Including the backbone and the ribs. That basically means that the turtle can’t leave the shell.
Turtle shell is covered with bony scales (also called scutes). Scales are made of keratin. Substance found in hair and nails of other animals. Melanin in scutes is the reason for various pigmentation and different designs.
But no all turtles have horny scales. Leatherbacks and soft-shelled turtles shell is covered with leathery skin instead.
Shape, support and protection of the shell is provided by the bony layer underneath the outer layer.
When turtles hatch, their plates are not connected in any way. But over the time the plates will slowly grow and fuse together. With keratin turtle shell has amazing regenerative abilities. If part of shell is damaged it will slowly heal overtime.
Aquatic turtles have light shells adopted for swimming. Shells of water turtles also contain large spaces between the shell bones. Also called fontanelles. Fontanelles additionally decrease the weight of turtle shell.
Land turtles (tortoises) have heavy shells for better protection.
Turtle shells vary in color. Commonly they are brown, black or green. Some species also have spots or lines in different colors.
When looking at turtle shell we can tell how particular species live. Majority of tortoises have large, dome shaped shells. Such shells make difficult for predators to crush it with their jaws. While aquatic turtles have flat and streamlined shell. Such shell is designed for improved swimming and diving.
Most turtles that spend most of their lives on land have their eyes looking down at objects in front of them. Some aquatic turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the top of the head. These species of turtles can hide from predators in shallow water, where they lie entirely submerged except for their eyes and nostrils. Sea turtles have glands near their eyes. Glands function is to produce salty tears. That way sea turtles can get rid of their excess salt intake.
Turtles are thought to have exceptional night vision due to the unusually large number of rod cells in their retinas. Turtles have color vision with a wealth of cone subtypes with sensitivities ranging from the near ultraviolet (UV A) to red. Some land turtles have very poor pursuit movement abilities, which are normally reserved for predators that hunt quick-moving prey, but carnivorous turtles are able to move their heads quickly to snap.
Turtles have a rigid beak. Turtles use their jaws to cut and chew food. Instead of teeth, the upper and lower jaws of the turtle are covered by horny ridges. Carnivorous turtles tend to have knife-sharp ridges for slicing their prey. Herbivorous turtles have serrated-edged ridges used to cut through hard plants. Turtles use their tongues to swallow food, but unlike most reptiles, they cannot stick out their tongues in order to catch food.
Terrestrial tortoises have short, sturdy feet. Tortoises are known for moving slowly, in part because of their heavy shell.
The amphibious turtles normally have limbs similar to those of tortoises, except the feet are webbed and often have long claws. These turtles swim using all four feet in a way similar to the dog paddle, with the feet on the left and right side of the body alternately providing thrust. Large turtles tend to swim less than smaller ones, and the very big species, such as alligator snapping turtles, hardly swim at all, preferring to simply walk along the bottom of the river or lake. As well as webbed feet, turtles have very long claws, used to help them clamber onto riverbanks and floating logs, upon which they like to bask. Male turtles have long claws, used to stimulate the females in mating periods. While most turtles have webbed feet, some, such as the pig-nosed turtle, have true flippers, with the digits being fused into paddles and the claws being relatively small. These species swim in the same way as sea turtles.
Sea turtles are almost entirely aquatic and have flippers instead of feet. Sea turtles fly through the water, using the up-and-down motion of the front flippers to generate thrust; the back feet are not used for propulsion, but may be used as rudders for steering. Compared with freshwater turtles, sea turtles have very limited mobility on land, and apart from the dash from the nest to the sea as hatchlings, male sea turtles normally never leave the sea. Females must come back onto land to lay eggs. They move very slowly dragging themselves forward with their flippers.
Skin and molting
As mentioned before, the outer layer of the shell is part of the skin; each scute (or plate) on the shell corresponds to a single modified scale. The remainder of the skin is composed of skin with much smaller scales, similar to the skin of other reptiles. Turtles do not molt their skins all at once, as snakes do, but continuously, in small pieces. When kept in aquaria, small sheets of dead skin can be seen in the water (often appearing to be a thin piece of plastic) having been sloughed off when the animal deliberately rubs itself against a piece of wood or stone. Tortoises also shed skin, but a lot of dead skin is allowed to accumulate into thick knobs and plates that provide protection to parts of the body outside the shell.
- Trachea: the windpipe, which connects the larynx and bronchi of the tortoise
- Lung: respiratory organ of the tortoise
- Stomach: part of the digestive tract of the tortoise between the esophagus and the intestine
- Pancreas: gland in the tortoise that produces digestive enzymes
- Rectum: final part of the tortoise’s digestive tract
- Anus: outlet of the tortoise’s digestive tract
- Bladder: pocket in which urine collects before it is evacuated
- Ovary: egg-producing reproductive gland
- Intestine: part of the digestive tract of the tortoise after the stomach
- Liver: bile-producing digestive gland
- Heart: blood-pumping organ of the tortoise
- Esophagus: part of the digestive tract of a tortoise between the mouth and the stomach
The rigid shell means turtles cannot breathe as other reptiles do, by changing the volume of their chest cavity via expansion and contraction of the ribs. Instead, turtles breathe in two ways. First, they employ buccal pumping, pulling air into their mouth, then pushing it into the lungs via oscillations of the floor of the throat. Secondly, by contracting the abdominal muscles that cover the posterior opening of the shell, the internal volume of the shell increases, drawing air into the lungs, allowing these muscles to function in much the same way as the mammalian diaphragm.
Mouth, Pharynx and Cloaca
Food, water and other nutrients are ingested into two main cavities in most turtles, the mouth and the pharynx. These two cavities are located inside of a turtles skull. However, sea turtles also have the ability to take in oxygen through their cloaca. This special feature is used in extreme situation typically to keep the turtle alive when oxygen levels are low (i.e. deep sea diving, hibernation).
Glottis and Larynx
The glottis of the turtle is a small opening positioned behind the tongue that acts as a barrier between the pharynx and the larynx when swimming underwater, diving or eating. The larynx is connected to the glottis and leads to the trachea. It is considered to be the upper most portion of the respiratory duct.
If you have ever heard a turtle hiss and wonder if it means that they are mad…rest assured, they are not mad. They are just frightened. When frightened they need to pull their head and legs into the shell, but because of full inflated lungs they won’t quite fit in. What they do is to expel the air within their lungs out as fast as they can, so that they will have room for their appendages to fit into the security of their hard shells. With rush of air leaving their bodies, turtle makes a hissing noise. That way many believe the turtle is ticked off and warning them to stay away.
Most vertebrates have similar digestive systems and the turtle is no exception. Turtles are not strictly herbivores. All species are found to eat at least some meat which causes them to have powerful digestive enzymes. In addition turtles swallow their food with very little chewing. Food particles are often whole or in fairly large chunks. The salivary glands of the turtle help to soften and break down the food to make swallowing possible.
Mouth and Tongue
The mouth of a turtle is a cavity found inside its skull. The tongue is flat and wide and fastened securely to the bottom of its mouth to prevent it from moving. Air, water, food and other essential nutrients enter the turtle’s body most often by way of the mouth.
Esophagus and Stomach
The esophagus is tubular, digestive structure that is connected to the stomach. Powerful digestive enzymes and acids within the turtle’s stomach decompose the food. The walls of the organs in the digestive system are composed of smooth muscle that helps to push the food through the system and aids in decomposition of the food by churning during the digestive process.
Liver, Gall Bladder and Pancreas
The liver is the largest organ in the body of a turtle. The liver has numerous functions and capabilities among which one is bile production. The gall bladder, on the other hand, is a small organ hidden behind the liver. It transfers the bile produced in the liver to the small intestine in the digestive process. Finally, the pancreas sliver like gland located next to the small intestine. It aids in the digestive process by introducing digestive enzymes into the small intestine as well.
Small and Large Intestine
The small intestine is connected from the stomach to the large intestine. Villi (or villus singular) located on the small intestine wall absorb food into the body. The large intestine, which is also known as the colon, reabsorbs excess waste and water produced by the digestive system.
The last part of the digestive system, the anus is where the feces (or wastes) exit the turtle’s body.
- Skull: bony case of the brain of the tortoise
- Phalanges: small bones forming the fingers
- Humerus: arm bone
- Proscapular process: bone of pectoral girdle of a tortoise, situated in front of the coracoid
- Back bone: vertebral column of a tortoise
- Femur: thigh bone
- Tibia: one of the two leg bones
- Phalanges: small bones forming the toes
- Fibula: one of the two leg bones
- Pelvic girdle: set of bones to which the limbs of a tortoise are attached
- Coracoid: bone of the pectoral girdle of a tortoise
- Scapula: shoulder bone
- Radius: one of the two bones of the forearm
- Ulna: one of the two bones of the forearm
- Vertebra: each of the bones forming the spine of a tortoise
- Mandible: lower jaw of the tortoise
Bones make up the majority of the skeletal system in turtles as opposed to amphibians who have a large amount of cartilage in their system. Connective tissue in the turtles is mineralized and becomes bone and the interior of their bones consists of sponge like marrow.
The turtle skeleton is divided into two main sections, the endoskeleton and the ectoskeleton. The endoskeleton consists of all the internal bones and the ectoskeleton of a turtle is its shell. The endoskeleton is further divided into two subsections called the axial skeleton and the appendicular skeleton. The axial skeleton is made up of the skull and both the cervical and thoracic vertebrae. The appendicular skeleton on the other hand consists the remaining bones in the skeleton.
The nervous system of the sea turtle is composed of the brain, nerves and spinal cord. In addition, specialized cells called neurons are the signal transmitters throughout the system. The brain is the center of turtle’s nervous system and it is there that the impulses carried by the nerves from the sensory organs are processed. Although the brain of turtles is more advanced than an amphibian’s it is primitive in regards to birds and mammals. The spinal cord of the turtle extends down it’s back and is protected by the carapace vertebrae. It is through the spinal cord that the information is carried to and from the brain. Turtles exhibit all the same senses as most organisms but the sense of smell is most advanced.