Reptilia

Introduction:

• The class name refers to creeping or crawling mode of Locomotion. (Latin reptum - To creep or Crawl).
• The Mesozoic era was known as the “Golden age of Reptiles”.
• Study of reptiles is known as "Herpetology".
• Study of snakes is known as “Serpentology” or “Ophiology”.
• There are about 6000 living species of Reptiles in this World.

Detailed explanation:
 

General characteristics of class reptilia
 

Habit and habitat

• They were the first successful terrestrial vertebrates.
• Some are also found in aquatic habitat.

Body

• Their body is divided into the head, neck, trunk and tail.
• Their skin is dry, rough, cornified and without glands (to prevent evaporation and to adapt to terrestrial habitat)
• Snakes & Lizards shed their scales as skin casts.

Digestive system

• A well developed and complete alimentary canal along with digestive glands are present in the digestive system.
• Teeth are acrodont, pleurodont and thecodont type.
• Tongue is protrusible.
• Complete alimentary canal opens into a common chamber called cloaca, which opens to the exterior.

Respiration

• Pulmonary respiration i.e., respiration takes place by lungs throughout their life

Circulatory system

• Usually, a three-chambered heart is present i.e., 2 auricles and 1 partially divided ventricle.
• A four-chambered heart i.e. 2 auricles and 2 ventricles is present in crocodiles.
• Sinus venosus is ill developed and truncus arteriosus is absent.
• RBCs are oval,nucleated and filled with haemoglobin.
• Well developed hepatic portal system while ill developed renal portal system is present.

Excretion

• Kidneys are metanephric type which helps in excretion and osmoregulation.
• Urinary bladder may be present.
• They are mostly uricotelic for the conservation of water.

Skeleton System

• Body is covered by horny epidermal scales or scutes.
• Endoskeleton is bony.
• Monocondylic type skull is present i.e the skull has single occipital condyle.
• Ribs are present in the neck and thorax region

Locomotion

• If present, two pairs of limbs are present and each limb has five digits. Each digit has incurved nails. (Snakes are limbless)

Nervous system

• Brain is well developed.
• 12 - pairs of cranial nerves are present.
• Lateral line system is absent.
• They do not have external ear openings.
• Tympanum represents the ear.
• Jacobson's organ (olfactory) is present at the roof of the buccal cavity in Snakes.

Reproductive System

• Reproduction is sexual.
• They are unisexual i.e sexes are separate.
• Fertilisation is internal.
• One or two penis (Hemipenis) are found in male animals as copulatory organs.
• These are mostly oviparous.
• Eggs are leathery and cleidoic, i.e. eggs are covered by a shell made up of CaCO3, to prevent dessication.

Development

• Development is direct i.e. larval stages are not formed.

Special adaptive features

• Parental care is a well marked characteristic.
• In reptiles, birds and mammals, all the three embryonic membranes amnion, chorion and allantois are present in the embryo. Yolk sac is also attached with embryos.
• These classes are grouped under the Amniota group, so reptiles are first amniotes.
• They are Poikilotherms (cold blooded animals) i.e. they can’t regulate their body temperature.

Classification of Reptilia
 

Living Reptiles are divided into the following subclass -
 

1. Sub - class Anapsida

• Skull has a solid bony roof.
• It includes only single living order chelonia
• Example - Chelone (turtle), Testudo (Tortoise)
  
  
   

2. Sub - class Diapsida

• Skull has two temporal vacuities.
• It is divided into three living orders

(a). Order Rhynchocephalia

• Example: Sphenodon (Tuatara) - a living fossil.

(b). Order Squamata

• It includes lizards and snakes.
• Examples of Lizards

1. Chameleon (Tree lizard) - Show metachrosis
 

2. Calotes (Garden lizard)
3. Hemidactylus (Wall lizard)
4. Draco (flying lizard)
5. Heloderma (gila monster)
6. Varanus (monitor lizard/chomododrago) - largest living lizard
7. Ophiosaurus (limbless lizard/ Glass snake)

• Examples of snakes

1. Naja Naja (Cobra)
 

2. Bangarus (Krait)
3. Vipera (Viper)
4. Hydrophis
5. Crotalus (rattlesnake)
6. Python (Ajgar)

(c) Crocodilia

Examples -
1. Crocodilus (Crocodile)
 

2. Alligator (Alligator)
3. Gavialis (Gharial)

Frequently Asked Questions: FAQs
 

Q1. Which era is known as the era of “Golden age of Reptiles”
Ans :

• The Mesozoic era was known as the “Golden age of Reptiles”.

Q2. How many chambered hearts do crocodiles have ?
Ans :

• A four-chambered heart i.e. 2 auricles and 2 ventricles is present in crocodiles.

Q3. What is the exoskeleton of reptiles made up of ?
Ans :

• The exoskeleton of reptiles is made up of horny epidermal scales or scutes.

Q4. Name any two poisonous snakes.
Ans : Naja Naja (Cobra) and Bangarus (Krait)

Q5. What is the egg shell of Reptiles made up of ?
Ans :

• The egg shell of Reptiles is made up of the crystals of CaCO3

Q6. Name any one living fossil of class Reptiles.
Ans : Sphenodon (Tuatara) - a living fossil.

Q7. What is the connecting link between amphibians and reptiles ?
Ans: Seymouria

Q8. Name the extra - embryonic membranes of Reptiles.
Ans :

• The three embryonic membranes of Reptiles are amnion, chorion and allantois are present in the embryo. Yolk sac is also attached to embryos.

Q9. Define metachrosis.
Ans :

• They show camouflage by changing the colour of the body according to their surroundings.

Q10. What is the study of snakes known as ?
Ans :

• Study of snakes is known as “Serpentology” or “Ophiology”.