Animal Information

Turtle and Tortoise BIOLOGY of Major Body SYSTEMS

Reptiles are ECTOTHERMIC, commonly called “cold blooded”. Turtle, found in the order Testudines. This is defined as any reptile with a body encased in a bony shell, including tortoises

Turtles and tortoises are unique reptiles belonging to the turtle order, Testudines. The Testudines are some of the most ancient reptiles alive, with only the tuataras considered more primitive.

There are approximately 300 living species and nearly 100 genera of Testudines, split into two suborders known as the Cryptodirans and the Pleurodirans with specially evolved biology.


Many people get confused when it comes classification

The Muscular System

The muscular system in turtles and tortoises is quite different from that of most other vertebrates. Muscles that are usually used to flex and twist in the backbone in nearly all animals are almost completely obsolete in turtles and tortoises due to their spine being rigid.

However, they have enormously well-developed muscles in their flexible necks, allowing them to retract into their shells.

They also have well-developed leg and tail muscles and possess considerably powerful muscles in their lower mandibles and if you have ever tried to pry open a reluctant tortoise’s mouth then you will have “felt” the full force of these muscles in action.

Check out Jamies bite!

The Digestive System

Although the turtle has the same digestive organs as most other vertebrates, it has adapted to cope extremely well in severe conditions where food and water conservation is at a premium.

Just like in a frog, food moves from pharynx (back of the throat) down the gullet into the esophagus to the stomach.

Acid secreted by the walls of the stomach and the stomach muscles work to break down food.

The pyloric sphincter muscle at the end of the stomach controls the passing of digested food into the small intestine. The upper portion of the small intestine closest to the stomach is the duodenum.

The next coiled section is the ileum. A fan-like membrane called the mesentery holds the folds of the small intestine together. The small intestine receives bile from the liver and pancreatic enzymes (including trypsin) from the pancreas. Digestion is completed here and nutrients are absorbed through the villi (small finger-like extensions) lining the small intestine.

The lower end of the small intestine leads into the large intestine (also called the colon), where undigested waste is collected and passed into the cloaca, a multipurpose cavity. Digestive waste, nitrogen waste from the kidneys (urine), as well as eggs and sperm all, pass through the cloasca on their way out of the body through the vent.

The tortoise can extract and assimilate moisture and nutrients from food items which to the human eye look completely “dried up” and would be of no nutritional benefit to most other living creatures.

Tortoises can achieve this using a “hindgut system” which is effectively like having two digestive tracts, the latter of which reabsorbs any moisture from the waste products already produced by the former. 

Arid habitat tortoises can also effectively split up their urinary waste in the kidneys, storing valuable water in the bladder and only expelling the waste product in the form of insoluble uric acid crystals. The crystals have a similar look to toothpaste when passed.

We show you what urates are in the video below! Click to watch these cute hatchlings get a soak.

In 1986 a study on the digestive tract of desert tortoises was conducted and confirmed that Cornified esophageal epithelial and numerous mucous glands along the digestive tract indicated resistance to abrasive diets. 

Gastric contents were acidic whereas hindgut digesta were near-neutral pH. The colon was the primary site of fermentation with short-chain fatty acids mainly comprised of acetate (69–84%), propionate (10–15%) and n-butyrate (1–12%). Fiber digestion was extensive and equivalent to 22–64% of digestible energy intakes. 

Large particles of grass were excreted as a pulse but retained longer than either fluids or fine particles. Patterns of marker excretion suggested irregular mixing of only the fluid and fine particulate digesta in the stomach and the colon. 

What Does This Mean?

Tortoises, in general, have a rather slow digestive process. The purpose of the slow digestion is to allow time for the microbial digestion of the plant cell walls so as to release the nutrients within and the production of additional nutrients by the microbes themselves for absorption in the colon like certain B vitamins, vitamin K and fatty acids.

The amino acids, proteins and certain other nutrients generated by these microbes are mostly lost as there is no means for them to be absorbed in the posterior (distal) colon.

Overall, hindgut fermentation does not produce great quantities of nutrients responsible for energy production. Although up to 30% may occur in the anterior (proximal) and mid colon, the majority occurs in the small intestines and ‘functional’ caecum (an eccentric dilation of the anterior colon in tortoises).

The relatively low energy available precludes hindgut fermentation from providing long-term sustenance. In almost all cases, prolonged activity during periods of extended fasting is fueled by fat reserves.

Once digested, the large masses of material are reduced considerably in volume. Interestingly, most food items are largely composed of water which is absorbed.

The utilized components of the diet comprise a surprisingly small percentage of the total mass consumed. Depending upon the food materials consumed defecation may occur from once every several days to multiple times per day.

Click to read more about Tortoise Gut Flora.


The main difference between a turtles’ respiration and ours is the volume of CO2 they can contain in their blood. Normally when we hold our breath, the CO2 in the blood makes us want to start breathing again, but tortoises are much more tolerable of this, allowing them to inhale less frequently.

If you startle a turtle or tortoise, its first reaction is to retract into the shell and the only way a tortoise can do this is by emptying its lungs. A frightened tortoise will consequently remain for some time with almost empty lungs whilst in this state.

Click to read more about Cloacal Respiration in Turtles.

Click to read more about CPR in Turtles and Tortoises.

Click to read more about Turtle and Tortoise Breathing Techniques.

Circulatory System and Heat Exchange

Turtles and Tortoises, like other reptiles, are cold-blooded or also known as being endothermic. This means they need to seek an external active heat source to keep their body at an optimum temperature range, enabling their vital organs to function properly.

Turtles do this by positioning their carapaces toward the sun or an artificial radiant heat source in captive situations. Reptiles have demonstrated this behavior long before evolution had even considered creating a mammal.

The coloration or “melanism” of a tortoise’s carapace varies by its geographical surroundings i.e. tortoises from extremely hot places like parts of Egypt and Morocco tend to be lighter in color.

This remarkable sign of evolution thus reflects some of the burning heat. Turkish Testudo Ibera, for example, is extremely melanistic, enabling them to absorb more heat.

A tortoise’s carapace incorporates tiny pores that help to trap in the radiant heat. Most noteworthy, you should never use any oils on their pet shell, as this will significantly hinder its thermoregulation capabilities.

However, there comes a time when one must treat topical fungus. One should wait until the weather is permitted before bathing and applying medications if possible.

Click to watch how we treat fungus at the reptile rescue we operate! It can take years to get these reptiles to rid their shells of this issue.

Just as ours, a tortoise’s heart pumps blood to all the vital organs and muscle groups, but a large amount of blood is also effectively sent underneath the carapace to “warm-up” before continuing to circulate the body.

An external basking temperature range of between 85-95°f is needed to allow the animal to internally thermoregulate its body temperature to the 90°f required for optimum metabolic efficiency.

The Senses


Turtles are extremely sensitive creatures. Despite popular belief, they can feel the slightest touch to their skin and shells. It was once thought that a tortoise’s carapace was void of any nerve endings, and as such horrific acts were often carried out and even recommended by media and literature of that time. This included drilling holes through the shells and tethering the animals.

Turtles CAN feel things that come in contact with their shells because they have nerve endings there, but they can not feel pain like you or I as they do not have those types of nerve endings. 

According to ZSL Publications, Neural impulses in response to tactile stimulation of the shell were recorded from afferent nerve fibers in tortoises T. graeca and T. hermanni. 

It was found that there is a mechanoreceptive innervation in the superficial layers of the shell which is sensitive to transient stimuli, particularly to vibration at frequencies up to 100 Hz.

Receptive fields pertaining to single and small groups of individual afferent fibers were mapped: the fields were sharply circumscribed and distributed in relation to the scutes of the shell.

The tactile innervation that was found would be consistent with a capacity for recognition and accurate localization of innocuous stimuli and may play a central role in courtship and mating behavior.


At the time of writing, there has been little study on the effectiveness of a tortoise’s eyesight. We know that tortoises have good all-around vision due to having their eyes at the side of their head as opposed to having a binocular vision like humans, but we do not know how sensitive or acute their vision is.

It is thought that tortoises certainly use their eyes to catch movement but perhaps have difficulty picking out detail. Some tortoise owners insist that their pet is fond of certain colors, often red.

Although whether it is an actual color preference or whether the animal is merely associating it with a favorite food item is open to debate.

Research shows that turtles see white light best; they are most attracted to the blue and green colors of the spectrum and turtles are least attracted to yellow.


Numerous publications have tried to give the impression that tortoises are virtually deaf, although it is fair to say that their hearing is significantly different from ours and perhaps less sensitive to high-frequency sounds, they are no means deaf.

The ears themselves have no external auricle and can be best described as simple ear “flaps” or “scales” which are located behind the tortoise’s eyes towards the rear of the head.


This is the primary sense that tortoise uses and it considerably more acute than most owners realize.

A tortoise relies heavily on scent for its daily activities including finding food, finding a mate, finding appropriate nesting areas, smelling for predators, etc. A tortoise uses smell for everything it does.


Despite their strange appearance and clumsy-looking way of rambling around, tortoises are very agile. They are incredible diggers and even better climbers; this is due, in part, to their excellent sense of balance. The sense of balance becomes even finer as the tortoise matures.

Hatchlings observed in captive situations always notoriously seem to end up on their backs, while adults seem to be sturdier on their feet, although this does vary from one individual to another.

What Is The Anatomical Difference Between Turtles and Tortoises?

One way to distinguish tortoises from other turtles is to look for certain anatomical features. The testudinids all share unique hind-limb anatomy made up of elephantine hind limbs and hind feet.

Their forelimbs are not flipperlike, and their hind feet are not webbed. Each digit in their forefeet and hind feet contains two or fewer phalanges. 

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