Chelonia A&P

Question 1

What are chelonia?

Answer 1

Tortoises, terrapins and turtles

Question 2

Describe the shell structure

Answer 2

Hard outer shell = carapace (covered with horny plates or scutes)
Flat ventral shell = plastron

The shell can feel sensation and pain

Question 3

Can they regulate their body temp?

Answer 3

No. They’re ectothermic

Question 4

What do they do to avoid extreme cold?

Answer 4

Brumate
Hibernation-like state that reptiles utilise in very cold weather. e.g. dormancy period.
Slower metabolism but not actually asleep.
Can go a long time without food but have to wake up to drink.

Question 5

What is the maternal care strategy of chelonia?

Answer 5

No maternal care. Oviparous

Occasionally guard the nest

Question 6

Describe the differences in outer appearance between tortoises, turtles and terrapins?

Answer 6

Tortoises - dry land, terrestrial species. Highly domed shell and elephantine feet. Forelimbs clad in large overlapping scales. Largely herbivores

Turtles - marine species. flatter shells. Largely carnivorous. Webbed feet, flipper-like.

Terrapin - freshwater
Webbed feet and claws. (multifunctional)
Largely carnivorous

Question 7

What is cryptodira?

Answer 7

Hidden neck.
Some spp Flex vertebrae vertically to pull neck back into shell. Some retract head straight back into shell.
2 strong muscles attaches the back of the skull to the point of fusion with the cervical vertebrae are responsible for the retraction of the head.

Question 8

What is pleurodira?

Answer 8

Side necked.
Flex vertebrae laterally to pull neck to side under shell.
All are freshwater aquatic

Question 9

Describe the skeleton of chelonia?

Answer 9

Not an exoskeleton but a modified ribcage and vertebrae. Pelvic and pectoral girdles lie within the ribcage (so the can pull the limbs inside the shell).
Ribs and backbones are fused to make the shell, covered in keratinised epidermis.
They do NOT have a sternum

Question 10

Describe the carapace of chelonia

Answer 10

Upper shell. Plates make up the inner bony layer.
Fusion of dermal bones, ribs, thoracic and lumbar vertebrae.
Scutes make up the horny outer layer

Question 11

Describe the scutes (large scales covering shell)

Answer 11

5 central (vertebral) scutes
4 lateral ( pleural/costal) scutes
Numerous marginal scutes
1 Nuchal scute (at head end)

Question 12

Describe the plastron

Answer 12

lower part of shell

also comprised of living dermal bone covered by keratinised epidermis.

Question 13

How are the plastron and carapace joined?

Answer 13

Joined by pillars of shell

Some species have hinges which open and close the shell.

Question 14

Describe the skull

Answer 14

Small to allow retraction
Sturdy with rigid upper and lower jaw
Posses a horny beak edged with keratin. No teeth

Question 15

What is unique about the elbow joint?

Answer 15

Elbow joint is rotated through 180 degrees

Question 16

Describe the toes

Answer 16

Most species have 5 toes.

Horsefield tortoises have 4 toes

Question 17

Describe respiratory anatomy

Answer 17

Paired nostrils
No hard palate
Trachea has complete cartilaginous rings and is short to allow the tortoise to breathe when head is retracted
2 lungs lie dorsal, just under the carapace

No diaphragm

Question 18

Describe respiration

Answer 18

Chelonia are nose-breathers
Lungs are not collapsible or expandable
Aided by head and limb movements which move in and out alternating the internal pressure in the body cavity.

Inspiration is achieved by increasing the lung volume by extending the limbs. This causes a decrease in lung air pressure and air is sucked in.
Expiration is achieved by retracting the limbs causing an increase in soft tissue and pressure within the coelomic cavity which forces air out of the lungs.

Question 19

What unique ability to chelonia have regarding respiration?

Answer 19

They can switch between aerobic and anaerobic respiration.
Respiration is aided by the water pressure which can draw in and out of the lungs.
Some freshwater turtles can absorb O2 via the cloaca
Some can also breathe through their skin.

Question 20

Describe their digestive system

Answer 20

Tongue is tightly attached and cannot protrude.
Rigid jaw and horny beak
Salivary glands only produce mucus - no digestive enzymes.
Simple stomach (spindle-shaped)
Small intestine relatively short
Wide LI for microbial digestion
Caecum present but not well-developed
Passage of food is slow for maximum absorption
Colon ends in the cloaca (3 sections)
Can bromate and go months without food.

Question 21

Describe the heart of the chelonia

Answer 21

3 chambered heart. Auscultation is aided by placing a damp towel over shell. Paired aorta and one ventricle.

Question 22

Describe the urinary system

Answer 22

Paired kidneys, caudally positioned and adhered to the ventral surface on inside of carapace.
Two ureters empty relatively unconcentrated urine into the urogenital sinus (opens into the urodeum) - also connects to the bladder.
Bladder is bilobed (2 lobes) and thin-walled and is capable of some reabsorption of water.

Question 23

Describe the reproductive system in males

Answer 23

Only 1 penis
Lies in the ventral aspect of the cloaca at rest. When engorged, it protrudes through the vent and curves cranially.
2 testes, epididymis, vas deferens, cloaca, vent (penis)

Question 24

Describe the reproductive system in females

Answer 24

Fertile eggs can be carried between 4 weeks and 4 years!
Can also store sperm for long periods.
Oviparous - lay amniotic eggs surrounded by tough protective shell
No maternal care
2 Ovaries - oviducts, magnus, isthmus, shell gland, vagina

Question 25

Describe the sexual dimorphism

Answer 25

Tail length and shell shape.
In tropical species - males are larger
In temperate species - females are larger

Some male terrapins have longer forelimb claws than females
Males may have a more concave plastron

Question 26

How is the sex of offspring determined?

Answer 26

Temperature.

Males are produced at lower temperatures than females - temperatures between can produce a mix

Question 27

Describe the senses

Answer 27

Vision - good colour vision. Have nictitating membrane.
Hearing - no external ear. Have eardrum, but poor hearing.
Have sense of smell and Jacobson’s organ

Question 28

Give examples of defence mechanisms in Chelonia

Answer 28

1. Arfican hingebacks
   - modified bony plates on their shells so they have a hinge
   - allows rear of shell to close inwards, protecting the back legs of the tortoise.
2. Box turtle
   - hinge of the plastron
   - when the turtle retracts the 2 halves close upwards towards the plastron sealing the turtle inside.
3. African pancake turtle
   - unusually soft and flat shell
   - hides in a crevice and expands so unable to remove it.
4. Snapping turtles
   - have a nasty bite