The external feature of sea turtles looks simple at the first sight with their limbs, head, and the shell, but internally it is quite complex!
Their anatomy is comprised of various organ systems like skeletal, circulatory, respiratory, nervous, digestive, reproductive, and excretory systems as described below.
Skeletal System
Anatomically the body of a sea turtle can be divided into two parts; outer or the Exo-skeleton and inner or the Endo-skeleton.
Exoskeleton
It is comprised of a bony shell, originated from their ribs and covers their body like a shield.
The shell of a turtle is a unique structure and gives a definite identity. It protects them and they take refuge within it in adverse conditions or during hibernation and covers their body except the limbs/flippers and head.
Shells are generally rigid and tough but sometimes soft and rubbery too. They are again divided into two parts; the carapace (the upper parts) and the plastron (the underside) which are laterally joined by bridges.
There are around fifty boney plates in the Carapace but only eleven in the plastron. Interestingly, the shells plates, which give support and strength, are composed of the layers of keratin and are regenerative too.
Endoskeleton
Inner or endoskeleton of turtles is made up of bones with spongy marrow inside. The bones are actually mineralized connective tissues. There are two subsections of the endoskeleton, namely the axial and the appendicular skeleton.
The Axial skeleton consists of the skull, thoracic vertebrae (10 vertebrae, fused with carapace) and cervical vertebrae (8 in number), while the Appendicular skeleton is made up of typical bones to support the pedal like front limbs to swim and rear limbs to steer through water.
Circulatory System
A three-chambered heart along with the artery, veins, and capillaries make this system.
Respiratory System
Their respiratory system is specially featured with Mouth, pharynx, Cloaca, Glottis, Larynx, Trachea, Bronchial tubes and 2 inflatable lungs (right and left) to contain extra oxygen for deep sea diving.
Nervous System
Consists of brain, spinal cord and nerves, neurons.
Digestive System
Mouth, Tongue, Esophagus, Stomach, Liver, Gall bladder, Pancreas, Small and Large intestine and Anus.
Reproductive System
The male and female reproductive organs produce sperm and eggs respectively. The females lay eggs and the sex of the hatchlings depends upon the surrounding temperature.
Excretory System
Two Kidneys with Salt glands, Bladder and Cloaca construct the excretory system of sea turtles.
