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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  

    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

    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' 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' Senses

  • 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.
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