The Turtles Shell
- Turtles shell is divided into two basic parts. The top is called the carapace and the bottom is the plastron.
- These sections are made up of fused bony plates. These fused bony sections are covered by protective shields made of keratin called scutes.
- The pattern of bone and scutes varies, so that the joints in each section do not overlap. This serves to reinforce the overall protection the shell provides.
- The divisions between scutes are called seams.
- Seams often leave impressions on the underlying bone, termed a sulcus.
- Every now and again most turtles will shed their scutes as new ones are grown underneath. They will begin to peal up and then eventually fall off.
- The pattern on the turtles scutes and scales often reflect the substrate that they naturally live in, allowing them to be better camouflaged.
- The Carapace contains about 50 bones.
- The most anterior bone along the mid-line is the Nuchal Bone.
- The nuchal bone is followed by 8 Neurals, 2 Suprapygals, & a Pygal in this order.
- In some species a Preneural may be present between the nuchal and first neural.
- On each side of the neural bones the Coastal Bones are present.
- In some species Precoastal Bones may be present.
- Outside the coastals & extending along each side from the nuchal to the pygal is a series of 11 Peripheral Bones.
- The most anterior bones of the plastron are the 2 Epiplastron Bones.
- The epiplastron bones are followed by a Entoplastron Bone.
- The next set of bones are the 2 Hyoplastra.
- Behind these are set of 2 Hypoplastra and 2 Xiphiplastra, in order.
- In some species a pair of Mesoplastra occur between the hyoplastra & hypoplastra.
Turtles' Respiratory System
- Turtles do not use gular pumping to breath, as some amphibians do.
- Rhythmic contraction and relaxation of some of the muscles between the forelegs and beneath the intestines allow air to be inhaled and exhaled.
- What appears to be gular breathing is actually related to olfactory significance.
- In WATER- inspiration depends on muscular movement and expiration happens virtually spontaneously.
- Turtles lungs are in the form of sacs with a variety of internal folds and chambers.
- Turtles with lighter weight shells have smaller lungs.
- As lung size increases with the intake of oxygen the bladder and cloacal sack secrete fluids to make room inside the body.
- In studies Musk Turtles have survived in a pure nitrogen environment for half a day. A mammal would die in minutes.
Turtles' Circulatory System
- The heart is situated in a fairly forward position, between the two lungs and resting against the inner front part of the plastron.
- Chelonian hearts are comprised of three chambers, although a partial septum is present within the ventricle.
- Temperature changes heart rate. Temp. goes up heart rate goes up. Temp. drops and the heart rate drops.
- Aquatic turtles release oxygen into their tissue quite rapidly.
- Aquatic turtles have high levels of carbon dioxide in their blood, because this helps protect them from the effects of metabolic acidosis.
Turtles' Digestive System
- Turtles do not have teeth. Instead they rely on the sharp cutting edge on their jaw and use their feet to tear food while holding it in their mouth.
- Turtles have a thick vascular tongue that is anchored rigidly to the floor of the mouth. It serves to direct food down to its stomach.
- The digestive tract is adapted to the feeding habits of each particular species.
- Predominantly herbivorous turtles have greatly elongated intestines to help digest their food. Highly domed carapaces help accommodate the extra bulk.
- Age changes the turtles diet. When a turtle is young it is primarily carnivorous but as the turtle ages they turn to a more herbivorous diet.
- Temperature plays a roll in influencing how long it takes food to pass through the digestive tract.
- Turtles have a large Pineal Body. This is their inner clock and helps them in responding to changes in day length and also has hormonal significance.
- Turtles have highly developed vision and can see colors.
- On many aquatic turtles the head markings continue on to the irides of the eye and this disruptive coloration serves a protection function.
- The eyes are protected by heavy eye lids.
- Turtles heavily rely on smell and it is believed that they can smell scents underwater.
- Throat movements(gular pumping) moves scent molecules over the jacobsen's organ in the oral cavity.
- Water drawn in through the nostrils may also pass over olfactory sensors.
- A few species may have taste buds present in their mouth.
- Turtles can only hear low auditory tones.
- Although turtles may not be able to hear the best they easily feel vibrations which help forewarn them to dangers.