Describe the eye position of reptiles
Near the front of the skull as predator species
Describe the teeth of reptiles
Peg-like teeth arranged in rows along the jaw
Teeth in mandible not attached in sockets unlike mammals.
What is a pleurodont?
Teeth are continually shed and replaced
What is an Acrodont?
Teeth are not replaced
What is the cloaca?
Chamber into which the GI, urinary and reproductive tracts meet
Describe the skin of reptiles
Thick keratinised epidermis forming scales. It is thin and fragile post-shed (ecdysis)
Describe the respiratory system of reptiles
Rely on their ribcage for inspiration
Cant cough and therefore more prone to aspiration pneumonia
Describe the urinary system of reptiles?
Can produce thick/turbid urine with mineral deposits in it
Have a bladder
No loops of Henle
Describe the reproductive system of reptiles
Oviparous - lay eggs
(some eggs dissolve internally and can appear to birth live young - oviviviparous)
2 ovaries, 2 oviducts, 2 infundibulum, 2 magnum, merge at isthmus, shell gland, vagina, urodeum.
Males have 2 testes cranial to kidneys, 2 vas deferens.
Males have hemipenes (inverted sacs at the base of the tail which evert to reproduce). Dorsal groove.
Reptiles are ectothermic. What does this mean?
Unable to alter their internal body temperature so use the external environmental temp to do so e.g. basking in the sun
Describe the anatomy of snakes body
Coelomic body cavity - no separate thorax or abdomen.
Describe the Skull of the snake
Described as kinetic
Solid and complete brain case
Large nasal cavity
Describe the Jaw of snakes
Separate left and right lower jaw joined by mandibular symphysis. Each half can move independently and are joined by an elastic ligament. There is no temporomandibular joint, the jaw is attached to a quadrate bone which allows further mobility - allows vertical and horizontal rotation of the jaw.
The maxilla is also only loosely attached tot he rostral aspect of the skull allowing nose to be lifted and making the oral aperture wider.
Yawn after eating to realign jaw.
Describe the sensory perception of snakes
Mandible and quadrate bones can pick up vibrations on the ground. Can detect position of prey
Describe the dentition of snakes?
Maxilla has 2 rows of teeth on each side (except fanged snakes which only have 1)
Mandible has 1 row of teeth on each side
Non-venomous snakes don’t have fangs.
Fangs point backward to secure prey and have a groove or are hollow for venom to run down.
All teeth are replaced as required
Fangs can be erect or fixed
Describe the vestigial limbs in snakes
Do not have thoracic limbs but do posses vestigial pelvic limbs. They are seen as external spurs in the pelvic region of species including boas and pythons.
Boas have the remains of a pelvic girdle and hind limbs, more evolved species don’t have a girdle.
Describe the ribs of snakes
Don’t join ventrally - no sternum!
All vertebrae have ribs attached except caudal vertebrae.
Function to protect organs, contribute to respiration and attachment for muscles for movement.
Describe the skin surface of snakes
Keratinised folded outer layer of epidermis covers whole surface.
dorsal and lateral scales are smaller; ventral scales are thicker and larger.
Snakes can have ventral scutes - a single row of scales. The more scutes, the faster the snake
Describe the eyes of the snake
No moveable eyelids
Eyelids have become fused together and become transparent - forming spectacles over the cornea.
Little or no skin glands
Describe the process of ecdysis
Shedding of scales head first.
complete outer layer (including the spectacle) is shed in one section with new skin layer beneath.
Occurs about 1-4 times per year
Snake will be dull and anorexic pre-shed
Protein-rich fluid is secreted between the old and new layers, pushing the old layer off. Once separate, the fluid is reabsorbed and the skin sloughs off.
Describe infrared sensitivity in snakes
Pit organs lie just between nostril and eye.
Used to detect prey by heat changes.
Can also help thermoregulation as can detect the surface temperatures in the environment.
Describe the ears of snakes
Do not have an external ear drum/ tympanic membrane or middle ear cavity.
Describe how snakes smell
Forked tongue provides a directional sense of smell and taste. It is in constant motion and used to detect prey and danger.
Then it passes onto the vomeronasal organ (or Jacobson’s Organ) in the mouth which has many nerve endings.
Describe the digestive system of snakes
The tongue can be forced out of the closed mouth via a labial notch.
The oesophagus is extremely distensible
The stomach is strong, elongated and elastic. It has very powerful juices to digest the whole prey.
The majority of digestion takes place in the stomach with a small amount happening in the small intestine.
The only substance that cannot be digested is hair and this is passed in faeces. Small intestine is relatively short, reflecting a carnivorous diet.
What effects digestive efficiency in snakes?
Temp between 25 &30 degrees will help. Too cold will slow or stop digestion which will cause problems with regurgitation and fermentation of food.
Describe the position of the spleen, pancreas and gall bladder in the snake
Found at the point where the pylorus empties into the small intestine. Some snakes has a splenopancreas - lightly adhered - so close they’re joined together.
Name and describe the 3 chambers of the cloaca in snakes
Coprodeum - faeces from LI received
Urodeum - receives urogenital ducts
Proctodeum - general collecting area for digestive and excretory wastes. The hemipenes also open into this portion
Describe the urinary system of snakes
Snakes have NO bladder
Snakes have no loops of henle and produce uric acid which is part of their adaption to preserving water.
U and F are passed through the same opening.
Describe respiration in snakes
No hard palate
Glottis allows breathing whilst eating by extending out of mouth. The glottis is rigid enough to withstand pressure when swallowing and opens when the snakes breathe.
Trachea has C-shaped cartilage rings
Lungs - large right lung and small or absent left lung. Some snakes have an air sac in place of a left lung.
Only anterior part of the lungs are for gas exchange. The posterior part is avascular and functions as an air sac that may act as a reserve during periods of apnoea.
Tracheal lung also present as an out-pouch of the lining of the trachea - helps breathing when the main lungs are being compressed by a large prey item.
Movement of ribs aids respiration as no diaphragm.
Describe the heart of a snake
3 chambered - 2 atria and one common ventricle
Heart is long and thin and quite mobile so larger prey items can pass by it.
Describe reproduction in male snakes
Testes are cranial to the kidneys. (R more cranial)
They enlarge during the breeding season.
Each has a vas deferens
Empties into the urodeum (where the sperm gets seminal fluid added to it)
Have hemipenes - paired penises. Lie in base of tail just caudal to the vent. Only use one at a time. Have barbs or spines and have a dorsal groove.
Describe reproduction in female snakes
Paired ovaries lie cranial to kidneys (R more cranial)
2 oviducts, 2infundibulum, 2 magnum.
Merges into the isthmus then uterus (shell gland) then opens into the vagina. Vagina empties into the urodeum.
They are seasonal breeders mostly
Describe sexual dimorphism in snakes
Can differentiate between species in some snake species by looking at colours and markings.
Surgical probe can be used. It will insert further towards the tail in males.
Males usually have a longer tail.
Male’s area around the tail can be swollen.
In some species the female is larger
Egg dissolves and absorbed internally and appear to birth live young.
Describe the digestive system of reptiles
Caecum present in herbivore species
Variety of tongue shapes. Tongue is used to ‘taste’ the environment in conjunction with the Jacobsen’s organ.
Simple, elongated stomach
Terminates the cloaca
On the diagram of the reptile skeleton, what bones are at the front of the forelimbs and hindlimbs?
Reptiles can exhibit autotomy. What does this mean?
Can drop body parts e.g. tail