Parts of a Turtle: Turtle Anatomy and Physiology (External & Internal)

In the wild, where mystery and wonder converge, turtles are fascinated by their appearance and body structure. Their timeless existence, shrouded in resilience and adaptation, beckons us to delve deeper into what is beneath their shells.

So, what are the parts of a turtle? Well, at the core of turtle’s anatomy is their hard shell, which is part of their skeletal structures. Their anatomy doesn’t stop at their shells. They have internal organs like the heart, digestion, and nervous systems, which are critical for their existence.

In this write-up, we will explore the intricate design of turtles, both external and internal. From their resilient shells to the hidden wonders of their physiology, we will journey through the depths of their anatomy.

External Turtle Anatomy and Physiology

Here is the external system of a turtle’s body:

A photo showing the external parts of a turtle [Source: Fauna Fondness]

1. Integumentary System

This system encompasses the external covering of a turtle. It safeguards it, facilitating essential functions. Here are the components of this system and their physiology in turtles:

• Skin and scales

Turtles’ skin varies in composition and texture depending on the species and habitat. Aquatic turtles have smooth and more streamlined skin. Their terrestrial counterparts have rough textured skin that aids in traction. 

As for scales, they are made of a protein called keratin. They provide protection against physical harm, environmental hazards, thermoregulation, and moisture retention. The skin and scales continue to grow throughout their lives and periodically shed for new ones to take shape.

• Shell

This is a defining feature of all turtles. It is a multifunctional component primarily composed of none covered in keratinized plate layers called scutes. The bone provides rigidity and support. The scutes offer additional protection. 

The shell is divided into two parts:

• Carapace: This is the upper or dorsal part of the shell. It forms a protective arch over the turtle’s back. The part also provides defense against predators and external threats. 
• Plastron: This is the lower or ventral part of the shell. Its main function is to protect the soft and vulnerable undersides of turtles. The underside has vital parts necessary for the existence of the animal. 
• Glands

Here is a table illustrating the glands these reptiles have:

Gland	Location	Function
Mucous glands	Distributed across the skin	Moisture retention and protection from parasites and pathogens
Salt glands	Near the eyes	Maintains osmotic balance in saline environments
Rathke glands	Varies by species. Some have two, one in the axillary inframarginal part and the other in the inguinal region.	Scent marking, territory establishment, and communication with other species.

• Coloration and Patterns

These are not mere aesthetics but crucial adaptations that play a critical role in turtles’ survival. Here is the physiology of their coloration and patterns:

• Thermoregulation: Dark-colored portions of the turtle’s skin absorb heat from the sun. This ensures that this cold-blooded animal raises their body temperature effectively to become more active.
• Camouflage: The patterns also blend into their natural habitats. This avoids detection by predators and prey.

Note that the coloration and patterns vary between different species. Common turtle hues include brown, olive green, black, yellow, orange, and red.

• Sensory Receptors

The Integumentary system of turtles is not just about protecting them externally. It also contains sensory receptors integral to a turtle’s ability to perceive and interact with the environment. Here is the anatomy of their sensors:

• Pressure-sensitive cells: These are scattered throughout their skin. The cells can detect changes in the turtle’s environment. When they come into contact with objects or other creatures, they signal the turtle. This is useful in navigating aquatic environments where visibility is limited.
• Olfactory organ: Turtles have two sensors in their nasal cavity. One is on the upper chamber of their epithelium, and the other is on the lower chamber. The two help it detect and respond to odors in the environment.

2. Limbs and Feet

Turtles have 4 limbs. Two front and two rear. They have the following physiology:

• Webbed feet: Aquatic turtles have webbed feet to function like paddles. This allows them to propel through water efficiently. Their terrestrial counterparts do not have webbed feet. 
• Long claws: These are common on terrestrial and semi-aquatic species. They help them have a good grip on floating wood and substances. They also help in ascending riverbanks, climbing over obstacles, and digging nests.
• Retractability: Turtles can retract all their limbs to their protective shell. This enhances their defense mechanism against predators.

3. Head and Neck Parts

Here is the anatomy and physiology of turtles’ head and necks:

• Head: The size and shape of the head vary with species. For instance, the heads of carnivorous turtles will be streamlined, thick, and masculine.

An image showing the size and shape of the heads of various species [Source: Gnaraloo Wilderness Foundation]

• Beak-like mouth: Species like hawksbill turtles have beak-like mouths. This enables them to find nourishment in hard-to-reach cracks and surfaces.
• Eyes: These are positioned on the sides of their heads. This placement gives them a broad vision field for proper navigation and predator detection.
• Nostrils: Nostrils are located on top of their beaks. They allow them to breathe. They can also close tightly when submerged to prevent water in the respiratory system.
• Flexible neck: Turtles have flexible necks, which enable them to reach their heads out for feeding, defense, and retracting them to the shells.
• Ears: These ancient creatures have ears at the sides of their heads. Their hearing is specifically sensitive to low frequencies, from 200 to 640 hertz. Any foreign vibrations within this range will trigger them to withdraw their heads back to the shell.

4. Tail

Do turtles have tails? Yes, and just like the rest of their anatomy, a turtle tail is a distinct feature finely tuned to fit their way of life. It has the following functions:

• Locomotion and balance
• Powerful propeller through water
• Houses sensory organs and receptors for environmental awareness

And just like the rest of the external parts, the tail is retractable to the shell. 

5. Reproductive Organs

Male turtles have hemipenes just beneath their tails. Female reproductive organs are also at the same spot. During reproduction, the male extends one of its hemipenes to transfer sperm to the female tract.

Internal Turtle Anatomy and Physiology

Below, we delve into the internal body parts of these aquatic and terrestrial reptiles:

1. Respiratory System

The respiratory system comprises the following parts and functionalities:

• Lungs: Turtles breathe through their lungs. Their lungs consist of multiple chambers separated by thin partitions. The design maximizes surface area for efficient gas exchange.
• Trachea: The main airway transports oxygen from the external environment to the lungs. And they do not have a diaphragm. For air to move through this tube, it relies on muscle contractions. 
• Glottis: The part is located at the base of the tongue. It connects the mouth cavity to the trachea. Its function is to control the flow of air. 
• Cloaca: All species have cloaca on their tail region. It enables them to extract oxygen from water. It enables them to survive in oxygen-depleted aquatic environments. 

2. Musculoskeletal System

This system is pivotal in supporting the turtles, enabling them to move and survive. It includes the following main parts:

• Endoskeleton: This is an internal framework made of bones. It provides support and protection to the internal organs. 
• Spine and ribs: The vertebral column runs along the dorsal aspect of a turtle. It is infused into the upper and lower shell, contributing to the turtle’s unique shell structure. 
• Limb bones: As mentioned earlier, turtles have four limbs, each with bones. They include the humerus (forelimb), radius, ulna, femur (hindlimb), tibia and fibula. All these bones provide support, mobility, and power for digging. 
• Scapula: Also known as the shoulder blade, this bone supports the forelimb, connecting it to the ribcage. 
• Ilium: This is a part of the turtle’s pelvic girdle. It forms the hip joint and connects the hindlimbs to the axial skeleton.

View of other parts of a turtle’s musculoskeletal system [Source: Ecomar Belize]

3. Cardiovascular System

Venturing further into their internal anatomy, we uncover the intricacies of their cardiovascular system. It includes the following main parts:

• Heart: At the core of this system is the heart. A turtle’s heart has three chambers, two atria, and one ventricle. The design separates oxygenated and deoxygenated blood. 
• Circulatory loops: These reptiles have two separate loops, the pulmonary and systemic circuits. The former transports blood between the heart and lungs. The latter carries blood to the rest of the body. 
• Blood vessels: Turtles have a network of veins and arteries. These carry blood to and from different body parts.
• Blood composition: Their blood has white cells, plasma, and platelets. It also has hemoglobin to transport oxygen.

4. Nervous System

The Central Nervous System (CNS) is at the heart of Internal physiology. CNS comprises:

• Brain: The turtle brain is small but complex also. It is located in the head cavity and is divided into specific regions, each having specific functions. For instance, the cerebrum is involved in complex behaviors and sensory processing. The cerebellum coordinates balance and motor skills. Other regions control functions like breathing and heart rate. 
• Spinal cord: It extends from the base of the brain down through the vertebral column. It is a crucial relay center for sensory and motor information. 

The nervous system also comprises the Peripheral Nervous System (PNS), which extends the CNS to the rest of the body. It includes neurons that transmit signals between the body and the CNS.

5. Gastrointestinal System

The gastrointestinal system is responsible for digestion and nutrient absorption. It comprises the following main parts:

• Oral cavity: The digestive journey begins in the oral cavity. This is where food captured by their beaks enters. But do turtles have teeth? Well, no. Their beaks can do most of the functions teeth have.
• Esophagus: Once ingested, food travels down to the esophagus. This is a muscular tube that connects to the stomach. It has contractions, known as peristalsis, to push food down. 
• Stomach: Turtle stomach is simple. It secretes gastric juices like hydrochloric acid and digestive enzymes that break down the food for digestion. 
• Small intestines: Here is where the majority of nutrient absorption occurs. The tube connects to large intestines. 
• Cecum: This is a pouch-like structure at the junction of small and large intestines. It contains symbiotic microorganisms that aid in digesting cellulose. 
• Large intestines: This tube absorbs water and electrolytes from the remaining undigested material.
• Cloaca: This is basically their anus. But it’s known as cloaca (Latin word for “sewer”) because it also functions as a gaseous exchange medium in aquatic environments. 

Conclusion

The above parts of a turtle: Turtle anatomy and physiology of their external and internal parts have opened your understanding of these mesmerizing creatures. These ancient beings have lots of systems in their body that have many body parts. 

From their integumentary system,  you now know their inner workings, consisting of their intricate skin and scales and internal marvels. The odyssey through the above turtle anatomy and physiology reaffirms the boundless wonders of the natural world.