Turtles 202

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.

Carapace Bones

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.

Plastron 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 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.

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 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.