CLASSIFICATION OF REPTILES

Written by Friday, 30 June 2017 21:58
Based on characters Reptiles is divided into Four sub class
 
  • ANAPSIDA
  • PARAPSIDA
  • DIAPSIDA
  • SYNAPSIDA
 
1. Sub-class: Anapsida:
 
  1. The skull of Reptiles are made by solid roof.
  2. In these Reptiles temporal vacuities are absent in the skull.
  3. In these Reptiles the quadrate is articulated with Otic bone.
  4. Limbs are strong.
  • Carapace and plastron will form the body covering.
 
This subclass is divided into two orders.
 
  1. Cotylosauria
  2. Chelonia
 
Order: Cotylosauria:
 
  1. These Reptiles are extinct.
  2. They show complete cranial roof.
  3. Pelvic girdle is flat.
  4. In these Reptiles Jaws and teeth are poorly developed.
 
These Reptiles resemble with Labyrinthodont Amphibians.

They became extinct in the triassic period of Mesozoic era.
 
Ex: Seymauria and Lepidosaurus.
 
Seymauria Lepidosaurus thumb12
 
Order: Chelonia:
 
This order includes Turtles and Tortoises.
 
Chelone turtle thumb13
 
  1. These are Terrestrial or aquatic.
  2. Body is covered by shell containing dorsal carapace and ventral plastron.
  3. Neck, limbs and tail are covered with scales.
  4. They show 4 limbs. pentadactyle are, modified into paddles in aquatic forms.
  5. Jaws without teeth.
  6. Jaws show horny sheaths.
  7. Quadrate is immovably articulate.
  8. Nasal opening is single.
  9. Unpaired copulatory organs are present.
  10. Cloacal opening is longitudinal.
  11. These are Oviparous.

Ex: Thonyx (Soft river terrapin), Testudo (Land tortoise). Chelone (Turtle).
 
2. Sub-class: Parapsida:
 
  1. This group includes extinct forms.
  2. Those forms lived from Triasslac period to cretaceous period.
  3. Their skull shows one pair of temporal vacuities. They are supratemporal fossae.
 
Ex: lchthyosaurus, plesiosaurus.
 
3. Sub-class: Diapsida:
 
  1. In these Reptiles skull shows two temporal vacuities.
  2. Modification of typical diapsid condition is common among these members.
 
This subclass is divided into two super orders Lëpidosauria and Archosauria.
 
Super Order: Lepldoauiia:
 
  1. These are primitive reptiles.
  2. Teeth are present on the palate jaw margins. They are not present in Sockets.

This super order includes two living orders.

1) Rhynchocephalia 2) Squamata.
 
Order: Rhinchocephaiia:
 
  1. Teeth are acrodont.
  2. The skull shows two vacuities.
  3. Quadrate bone is immovable.
  4. An epipterygoid bone is present
  5. Vertebrae are Amphicoelous.
  6. Copulatory organs are absent in this order.
 
Ex: Sphenodon (Newzealand)
 
reptiles2 thumb9
 
Order: Squamata:
 
This includes Snakes & Lizards.
 
  1. Their body is covered by epidermal scales.
  2. Single supra temporaI vacuity is seen in lizards and temporal vacuity Is absent In snakes.
  3. Teeth are pleurodont.
  4. Usually procoelous vertebrae are present.
  5. Transverse cloacal opening is piesent.
  6. Male shows a pair of eversible copulatory organs, useful for copulation.
 
This is divided into two suborders.
 
Sub Order: Lacertilia:
 
  1. These are terrestrial, arboreal or burrowing forms.
  2. Limbs &re pentadactyl and are usually present.
  3. Sternum is present.
  4. Eyelids are movable.
  5. Tympanum is present.
 
Ex: Calotes, Chamaeleon, Draco, Varanus, Gecko.
 
Sub Order: Ophidia:
 
This sub order includes snakes.
 
  1. They are terrestrial or aquatic, or arboreal or burrowing forms.
  2. Temporal vacuities are absent.
  3. Limbs and limb girdles are absent.
  4. Sternum is absent.
  5. Eyelids are absent.
  6. Tympanum is absent.
  7. Tongue is bifid.
 
Ex: Python , Lycodon, Naja naja, Hydrophis, Viper.
 
chameleon reptiles thumb17
 
Super Order: Archosauria:

This includes advanced reptiles.
 
  1. Teeth are on jaw margins and are set in muscular sockets.
  2. This super order includes a single living order Crocodilia.
 
Order: Crocodilia:
 
  1. These are fresh water and predatory forms.
  2. Body is covered by an exoskeleton made by horny’ scales & scute.
  3. Teeth are thecodont.
  4. Quadrate is immovable.
  5. Vertebrae are procoelous.
  6. Spongy lungs are seen.
  7. Longitudinal cloacal opening is present.

Ex: Crocodilus, Alligator, Gavialis
 
Crocodilia Gavialis thumb18

4. Sub-class: Synapsida:
 
  1. This group includes all extinct forms.
  2. They lived from carboniferous to permen period.
  3. Their skull shows one pair ot Vacuities. These vacuities are infratemporal fossal.
 
Ex: Dimetrodon, Cynognathus.

GENERAL CHARACTERS OF REPTILES

Written by Friday, 30 June 2017 21:25
AN INTRODUCTION TO REPTILES
 
In the carboniferous period of palaeozoic era “Reptiles” arose from Labyrinthodont Amphibians. In the Mesozoic era “Reptiles” dominated the entire world and that era is called "GOLDEN AGE OF REPTILES".
 
Cotylosauria’ is considered as “stem - reptiles”. They closely resemble the Labyrinthodont amphibians. It is not easy to distinguish these two groups separately.
 
In the Mesozoic era giant dinosaurs dominated the earth. In the late cretaceous period of Mesozoic era they became extinct.
 
In the present day world nearly 5,000 known species of reptiles are living. Reptiles are poikiothennic vertebrates. They are first true land vertebrate’s. They are the first amniotic group of vertebrate animals.
 
The Present day reptiles are sphenodon, lizards, snakes, turtles and crocodiles.
 
The Reptiles origin from labyrinthodont Amphibians in the carboniferous period of Paleozoic era. Present day living Reptiles are 5,000 species. They have an endoskeleton of dry epidermal scales and in some, bony dermal plates are present.
 
The Reptiles flourished in the Mesozoic era. Gant Dinosaurs dominated the earth and seas. Mesozoic era is the “Golden age of Reptiies”. Most of the giant Reptiles became extinct in late cretaceous period of Mesozoic era era.
 
GENERAL CHARACTERS OF REPTILES
 
  1. Reptiles are cold blooded Vertebrates.
  2. Reptiles are terrestrial (or) aquatic animals.
  3. The body of Reptiles is covered with horny scales (or) bonyscutes.
  4. In Reptiles Skin is dry.
  5. Glands are absent in the skin of Reptiles.
  6. Four limbs are present. They are pentadactyl (having 5 fingers).
  7. Skull occipital incompletely.
  8. In Reptiles Vertebrae are gastrocentrous.
  9. In Reptiles Ribs from a true sternum.
  10. Respiration is carried on by the lungs.
  11. In Reptiles Heart is divided into two auricles and ventricle is divided into2 chambers incompletely.
  12. Right & left aortic arches are completely formed.
  13. Red blood corpuscles are nucleated in Reptiles.
  14. In Reptiles Kidneys are meta nephric. Each kidney is provided with separate ureter.
  15. In Reptiles Twelve pairs of cranial nerves are seen.
  16. Cloaca is present.
  17. Fertilization is internal. Eggs are laid on land.
  18. In Reptiles Extra embryonic membranes are present during the development of the embryo.

PARENTAL CARE IN THE MEMBERS OF CLASS AMPHIBIA

Written by Friday, 30 June 2017 20:28
Amphibian include anurans, urodelans and apodans. In all these groups of amphibians we come across with a great deal of parental care. Amphibians show several mechanisms to protect their eggs and developing young ones because of the they lay few eggs.
 
Parents protect the eggs and early developmental stages in two ways.
 
  1. They construct nests
  2. Direct Nursing.
 
The female Icthyophis glulinosa will dig a hole in the moist soil near a pond. It will deposit eggs in it. Around this egg mass the mother will coil and. protect the egg mass from the enemies.

2. PARENTAL CARE IN E ORGANISMS CF URODELA:
 
In some urodela amphibians the eggs are very small. They hatch end directly develop into larvae. In those organisms parental care is not required.
 
a) Protection by Nests:
 
  1. Salamandrella keyserlingi will construct a gelatinous bag like structure. It is attached to an aquatic plant below the water. In this bag eggs are stored. Thus they are protected by the Nest.
  2. Autodax will lay eggs in a dry hole on the soil or in a hole on a free. The parents also live in the hole and protect the egg and the larvae developed from them.
 
b) Direct Nursing by Parents:
 
  1. Amphiuma, (Congoeel) The mother will coil around the eggs and protect them.
  2. Desmognathus fuscus, (the dusky Salamander) The mother will carry the eggs. They are attached around its neck.
  3. Salamandra salandra, (the European fire salamander): The mother will retain few eggs in its body. It liberates the larvae into water. They complete their development in the water.
  4. Salamandra atra, (the European alphine salamander): The mother keeps the eggs in its uterus. It liberates only the young ones which are completed their metamorphosis.
 
3. PARENTAL CARE IN ANURA AMPHIBIANS:
 
In Mura amphibians the parental care is reached its peak. Many organisms will exhibit parental care.
 
a) Protection by Nests:
 
Many frogs and toads build nests in which the eggs are laid and developed. This is a primitive method of parental care. In these organisms the larva comes out in a very early embryonic stage which requires some kind of protection in the very early stages of development, hence the parent will build nests.
 
  1. Hyla Faber: It is Brazilian free frog. The female will construct the nest in the shallow waters of a pond. The female will dig a hole of 8 to 10cm depth. The mud which comes out of it is used by the female Hyla to construct a wall around the hole. This wall is raisd’above the level of water. Female Hyla will make the inner surface of this Nursery smooth and even the female will lay eggs in this nursery. The eggs and larval forms are protected inside this structure.
  2. Rhacophorus malabaricus: It is called chunam frog. It lays eggs on the branches or leaves of a tree which will be hanging over a pond. These larvae after hatching from eggs will fall into the pond water and undergo metamorphosis.
  3. Rhacophorus schlegeli: It is called Japan free frog. Both male and female frog will make a burrow in the moist soil near a pond edge .This hole is filled with foam by female. Then female lays eggs in this foam. The male and female animals will make an exit tunnel into the pond from the hole. The larvae developed from eggs will be carried by the liquid formed from the foam into the pond through these exit tunnels.
  4. Hyla resinfectris: It is a free frog. It will make use of holes in the frees. It will line the hole of free trunk with beewax brought from bee comb. Female animal lays eggs in this hole when filled with rain water.
  5. Leptodactylus mystacinus: It digs a hole in the moist mud near a pond. This hole is filled with foam which is secretes by the oviducts of the female. Female lays eggs in it. These eggs hatch into larvae then the pond will get good amount of water from rain. Then these holes are also sunounded by the pond water, Then the larvae will enter the pond and grow.
  6. Hyla nebulosa: It lays its eggs in a nest. This nest is made by dry leaves. The eggs hatch and develop into small adults. Larval form is absent.
  7. Hylodes: It is an American frog. It deposits its eggs in moist places or under the stones. The eggs hatch and give tiny adults in perfect condition.
 
b) Direct Nursing by Parents:
 
This method is more advanced than protecting the eggs and larvae by constructing nests.
 
  1. Alytes: It Is called Mid-wife-toad. When the eggs are laid by the female frog winds the strings of eggs round his back and thighs. This male frog lives in a shallow pit of the moist soil, It will came out of the pit now and then for feeding and to make the eggs moist. When the eggs are ready to hatch the male frog moves to a near by pond and the larvae are released.
  2. Gastrotheca: It is called New World brooding (or) Marsupial frog. It has a special pouch in its skin. It opens out through an opening near the cloaca. Fertilized eggs are transferred into this pouch. The eggs are stored in this pouch where they ‘undergo development and tadpoles are liberated out.
  3. Pipa americana: It is called surinam toad. During breeding season the skin of the back of the female becomes soft and spongy. During copulation the oviducts will come out of the female. Because of the movements of male the eggs are forced out of the oviduct. Each egg sinks into a small pocket of the skin. It gets coveted by an operculum. In the soft maternal tissue the young one can develop safely. The developing embryo has a tail and yolk sac. It has no gills. The tail may work like placental connection to draw nutrition from the mother. Nearly after 80 days small individuals may come out.
  4. Rhinoderma darwini: It is called little South American frog. The fertilized eggs are transferred into its vocal sacs the development takes place. Then the completely developed young individual will jump out from the mouth of the male frog.
 
Thus in Amphibians a good  amount of parental care is seen.

PAEDOGENSIS OR NEOTENY IN AMPHIBIANS

Written by Friday, 30 June 2017 20:03
Neoteny is defined as the failure or delay of larva to metamorphose while becoming sexually mature. It is character of some amphibians.
 
The best example is axolotl larva of Amblystoma. It is aquatic. It has gills. It develops gonads. It lays eggs and attains large size. Amblystoma on the other hand, is terrestrial and without gills. It was considered the axtolotl as a separate genera in the beginning, with the administration of thyroxine, axtlotl lost its gills and develops lungs. It metamorphosed into the adult. Metamorphosis of axolotl can be induced by reducing the water level.
 
Proteus. and Necturus are permanently neotenous forms. They retained the larval features and reproduce sexually like a mature animal.
 
Kollman has distinguished two types of neoteny:
 
  1. Partial neoteny: Tadpoles of Hyla arborea, Rana escülenta during winter will show simple retardation of metamorphosis beyond the normal period.
  2. Total neoteny: It will retain its gills and becomes sexually mature.
 
Ex: Amblystoma.
 
Formerly full neotenic forms with external gills were considered as most primitive amphibians. But now it is believed that it is the result of secondary adaptive modifications in their larval stage.

CLASSIFICATION OF AMPHIBIA

Written by Friday, 30 June 2017 18:39
Based on characters of amphibians the present day (extant) amphibians are classified Into 3 orders.
 
  • Order 1. Anura - (Frogs and Toads)
  • Order 2. Urodela - (Salamanders)
  • Order 3. Apoda - (Limbless amphibians)
 
Order 1. Anura
 
This order Anura includes frogs and toads.
 
  1. They can live in water and on land.
  2. The fore limbs are small, the hind limbs are long.
  3. In the adult stage tail is absent
  4. They show a pair of eyes. tympanic membranes.
  5. Their Life history includes a larval stage called tad-pole larva.
 
Eg: 1. Alytes (Mid wife toad), 2. Cacopus (Burrowing frog), 3. Xenopus (Clawed Toad), 4. Bufo.
 
Order 2. Urodela
 
This order includes Salamandars and newts. These urodelans are more in North America. Hence North America is called Head Quarters of Urodela
 
  1. The body is divisible into head, trunk and tail. Only In these amphibians tail is present. Hence these are called Urodela.
  2. The fore limbs and hind limbs are equal.
  3. The body’s not covered by scales.
  4. In some adults the gills are presents
  5. Some forms show neoteny and paedogenesis. In North India only one species is available. Tilototriton venvcosa. In South India urodelan animals are absent.
 
Eg: 1. Necturus, 2. Proteus (Mud puppy), 3. Molge (Newt), 4. Amblystoma
 
Order 3. Apoda
 
  1. These animals are limbless. Hence they me called Apoda.
  2. The body is long and snake like. Hence it Is called gymnophiona. The body is divisible into head and hunk. Tail is absent
  3. On the head two eyes are present. They covered by skin and scales. Hence they are blind (Cecaelians).
  4. Lungs are asymetrical.
  5. The skin shows minute cycloid scales. in the male apoda animals copulatory organs present.
  6. Fertilization is internal.
 
Eg: 1. lchthyophis (Limbless amphibian), 2. Gegenophis (Limbless amphibian), 3. Ureotyphlus.

GENERAL CHARACTERS OF AMPHIBIA

Written by Friday, 30 June 2017 18:22
Amphibians are cold blooded vertebrates. In the Devonian period of palaeozoic era they were originated from fishes, in the carboniferous period, they increased their number, hence that period is called ‘Age of amphibians’.
 
According to Romer Dipnoi fishes are the “uncles of Amphibians” According to Newman “Dipnoi and amphibians had same grand father.”
 
General Characters of Amphibians
 
  1. Amphibians are cold blooded vertebrates which can hue on land and in water.
  2. Amphibians show four limbs with which they can swim in water and jump or walk on the land, (But in apoda limbs are absent.)
  3. In Amphibians  animals exoskeleton is absent. But in apoda animals small cycloid scales are present.
  4. In Amphibians the adult animals lungs are present. Gills are absent. But In some urodelans the gills are present.
  5. Amphibians Skin is a respiratory organ.
  6. The Amphibians skull is dicondylic.
  7. Amphibians Ribs are absent.
  8. In Amphibians The body divisible into head and trunk Tail is present in, urodela animals.
  9. Amphibians  Digestive system is well developed. A well developed liver Is present
  10. External ear is absent. Middle and inner ears are present, the middle ear columella auris Is present.
  11. Amphibians Heart is 3 chambered with 2 auricles and 1 ventricle The blood contains R.B.C. They are nucleated. They contain hemoglobin.
  12. Blood vascular system contain hepatic and renal portal systems.
  13. Amphibians Kidneys are mesonephric. Urinary bladder is present. It stores urine.
  14. Central nervous system is well developed. The brain occupies completely the cranial cavity. The brain is divided into fore, mid and hind brains. Brain continuous as spinal cord.
  15. 10 pairs of cranial nerves will arise.
  16. Sexes are separate.
  17. Male and female can be indentified - Sexual dimorphism.
  18. In Amphibians the life history a larva stage may be present.
  19. Amphibian Eggs are telolecithal, Cleavage is holoblastic unequal.

AN INTRODUCTION TO AMPHIBIANS

Written by Friday, 30 June 2017 18:07
Amphibians are the earliest tetrapods. They were descended from fish like ancestors. They were developed in the Devonian period. They flourished during carboniferous period. It is called “Age of Amphibians”.
 
AMPHIBIANS thumb16
 
Amphibians can lead their life on land and in water. They are cold blooded vertebrates. They show four pent dactyl limbs. They are supported by pectoral and pelvic girdles.
 
Their skin is soft. It is glandular. They do not how exoskeleton. They perform respiration by lungs and skin. In some amphibians gills are also seen. They show three chambered head. Their R.B.C. are nucleated. Sexes are separate.
 
In the present day world nearly 15000 species are living. They belong to only three order
 
1) Anura 2) Urodela 3) Apoda

AMPULIAE OF LORENZINI IN FISHES

Written by Friday, 30 June 2017 17:55
On the upper and lower surfaces of the head a number of tin- branched structures are present. They are called ampullae of lorenzini.

Each ampulla contains two parts.
 
  1. Expanded ampullary sac and
  2. A long narrow ampullary canal.
 
The ampullary sac contains 8 to 9 chambers. They are separated by septal walls. They are arranged around a central axis. These chambers contain sensory papillae. These sensory papillae are connected with nerve fibers.
The ampullary canal is long and narrow. It is filled with mucus. It opens out through a pore.
 
These sense organs will work as thermo receptors. They detect the temperature changes of the water. They also detect the changes in the pressure.

INTERNAL EAR OF SHARK (OR) MEMBRANOUS LABRYTH

Written by Friday, 30 June 2017 17:19
It lies in the auditory capsule of the skull. It is useful for maintenance of equilibrium. In the fish external and middle ears are absent. Internal eats covered by cartilaginous labyrinth. A space is present between membranous and labyrinth is filled with perilymph.
 
The membranous labyrinth shows laterally compressed sac. It is divided into utriculus and sacculus. At the end of the sacculus lagena is present.
 
The internal ear shows 3 semi circular canals.
 
  1. Anterior vertical semicircular canal.
  2. Posterior vertical semicircular canal.
  3. Horizontal semicircular canal.
 
These semicircular canals end with ampullae.
 
From the dorsal side of the internal ear duct arises. This is called saccus endolymphaticus. It opens out on the skin.
 
In the ampullae sensory patches are present, they will be acoustic in nature, in the utriculus and sacculus otholiths are present. They are mainly useful for maintenance of balance. Thus the internal ear is useful for caring and maintenance of balance.

CLASPERS IN SHARKS

Written by Friday, 30 June 2017 16:50
In male shark claspers are present. The claspers are rod like copulatory organs present on the inner borders of the pelvic fins. They are supported by carfilages. Each clasper has a groove on its dorsal side. The groove is opened at both the ends. Its anterior opening is called the apopyle and the posterior opening the hypopyle communicates with the cloaca. It receives the sperms from the cloaca. The hypopyle is as an exit for the sperms into the cloaca of the female.
 
CLASPERS SHARKS1 thumb8
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