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

OLFACTORY LOBES IN SHARKS

Written by Friday, 30 June 2017 16:31
In Scoliodon the olfactory lobes are olfactory organs or nasal sacs.
 
They are present in the olfactory sacs of cranium. They develop from the ectoderm. They open out through the exterior by external nostrils. Each nostril is divided into two parts. In current siphon and excurrent siphon.
 
Sharks Olfactory lobes thumb4
 
The olfactory lobe is lined by olfactory epithelial This epithelium Is called schneiderian membrane. it shows spindle like olfactory cells, sup porting cells and gland cells. The olfactory cells connected with a nerve fiber. All of them are united and olfactory nerve is formed. It will meet the olfactory lobe of the brain. Schneiderian membrane is folded. Hence the olfactory surface is increased.
 
The folds of two series are set a part by medina raphae. The olfactory cells are sensitive to the chemicals in the water.
On the lateral sides of think and tall lateral line canals are present. They are present deeply In the dermis. In the head region there are connected by transverse canals. In the head region cephalic canals are present
 
Neuromast thumb16
 
  1. Infra orbital
  2. Supra orbital
  3. Hyo mandibular
  4. Mandibular
 
Neuromast orgnan thumb18
 
From these lateral line and cephalic canals small tubes win arise and open on the skin. These canals are lined by epithelium. They contain gland cells. Recreceptors are present. The Chemoreceptor is (neuromast) group of spindle shaped neuro sensory. They are connected will nerves. The nerves connected with VII Cranial nerve.
 
The lateral line system detects waves and currents in water.

CLASSIFICATON OF PISCES (FISHES)

Written by Friday, 30 June 2017 00:44
The super class Gnathostomata includes craniates, in which one pair of the visceral arches is modified into this jaws. They how internal ear with three semi-circular canals and provided with paired 4, apdages (fins or limbs). Sexes are separate. The super class is divided into, two groups.
 
1) Pisces and 2) Tetrapoda.
 
Pisces Include three classes.
 
  1. Placodemi,
  2. Elasmobronchi (Chondrichthyes),
  3. Osteichthyes.
 
Muller, Goodrich. Berg, Romer etc, classified the Pisces. There is no agreement among many authors with respect to the classification of fishes.
 
Class 1: Placodermi (Aphstohyoids)
 
  1. It includes extinct fishes.
  2. They are all armored fishes. Their exoskeleton Is in the form of bony plates or shields.
  3. Their endoskeleton is bony:
  4. The hyoidean gill-slits are complete. It is not reduced.
  5. The autodiastylic jaw suspension is seen in these fishes.
  6. Heterocercal caudal fin is seen.
  7. Hyoid arch will not support the jaws.
  8. Primitive jaws are seen.
  9. They survived up to Permian period of Paleozoic era.
 
Ex: Climatius, Bothriolepis.
 
Class 2: Chondrlchthys or Elasmobranchi
 
  1. These fishes are exclusively marine.
  2. The exoskeleton in the form of placoid scales.
  3. Their endoskeleton is cartilagenous and are called Cartilage
  4. Jaw suspension is amphistylic or hyostylic.
  5. 5-7 pairs of gills are present.
  6. External gill openings are separate. They are not covered by operculum.
  7. Heterocercal caudalfin is seen.
  8. Males show claspers for copulation.
  9. Air-bladder is absent in these fishes.
 
The Class Elasmobranchi is divided into two sub-classes.
 
1. Sub-class Selachi:
 
In these fishes the pectoral fin has cartilagenous rods. Fins are well developed. The caudal fin is hetetocercal. This subclass has four orders in which only two are living.
 
Order 1. Proto selachi
 
  1. Jaws show many pointed teeth.
  2. Nasal openings are paired.
  3. Hyostylic or Axnphistylic jaw suspension.
 
It is represented by few living species.
 
Ex: Heteroloatas
 
Order 2. Euselachi
 
  1. Skin contains placoid scales.
  2. These fishes are exclusively marine.
  3. 5 pairs of gill slits. They open separately. It is divided into two
 
1. Sub-order Pleurotremata:
 
  1. Gill slits on the lateral sides of the body.
  2. Pectoral fins are distinct.
  3. It includes sharks and dog fishes.
 
Ex: Scoliodon, Sphyrna (Hammer headed shark), Stegostoma (Tiger shark).
 
2. Sub-order Hypotermata:
 
  1. It includes skates And Rays.
  2. The body is flattened dorso-ventrally.
  3. Pectoral fins are enormously expanded anterio posteriorly and gill openings are ventral and five in number.
  4. Dorsal fins, if present are seen on the tail.
 
Ex: Pristis (Saw fish), Rhinobatus (Guitar fish), Torpedo (Electric ray), Raja (Skates), Trygon (sling rays), Myliobatis (Eagle rays)
 
2. Sub-class Bradyodonti:
 
It includes fossil and modern chimaeras.
 
  1. Mouth is small and bounded by lips.
  2. Holostylic jaw suspension is seen.
  3. Gill opening are enclosed in boneless operculum.
  4. Male possesses a frontal clasper on the head.
 
It is divided into 2 orders.
 
Order 1. Eubradyodonti
 
‘It includes Helodus’.
 
Order 2. Holocephali
 
It includes chimaera. These are called devil fishes. Chimaera also called king of Hernngs.
 
Chimara king of herrings thumb16
 
Class 3: Osteichthyses a Telostomi
 
  1. These fishes are marine, fresh water and bracldsh water niem hers.
  2. Cycloid, ctenoid or ganoid scales will form the exoskeleton.
  3. Endoskeleton bony.
  4. Jaws suspension is autostylic
  5. Operculum is present.
  6. Claspers are absent
  7. Usually air bladder is present
 
This class is divided Into two sub-classes.
 
  • Sub-Class I. Crossopterygii
  • Sub-Class II. Actinopterygii
 
1. Sub-class Crossoptenygii:
 
In this sub-class bony fishes are Included which show lobed and massive fins. The sub-class includes two orders,
 
Order 1. Rhipidistia
 
This order includes extinct fishes. But in 1938 one coelacanth fish was caught. This was identified as, Rhipidistian fish by Miss. Latimer. The fish is called Latimeria. It is the oldest living fossil.
 
coelacanth Latimer thumb17
 
Order 2. Dipnoi
 
This order Includes living fishes. In the present day only 3 genera are living. They show discontinuous distribution.
 
Ex: 1. Neoceratodus (Australian lung fish), 2. Protopterus (African lung fish), 3. Lepldosiren (South American lung fish).
 
Dipnoi discontinuous distribution thumb24
 
2. Sub-class Actinopterigii:
 
These fishes will live in fresh water or marine water. They not show internal nostrils. This subclass is divided into three super orders.
 
Super Order 1. Chondrostei
 
This super order includes 3 orders, only fishes of one order or surving
 
1. Order Polypterifonnes
 
The fishes wtth ganoid scales Caudal fin is symmetrical. Dorsal fin has many peculiar fin-lets.
 
Ex: Polypterus.
 
Super Order 2. Holostel
 
This include 2 orders.
 
1. Order Amiiformes
 
Caudal fin is heterocercal. Ex Antia (Bowin).
 
2. Order Lepldoeteiformes
 
Nasal opening at the end of the much elongate snout. Caudal fin is abbreviate heterocercal.
 
Ex: Lepidpsteus (Gar pike).
 
Super Order 3. Telosteti
 
This is a very important super order. It includes nearly 25,000 species. They are divided into many orders.
 
1. Order Clupelfonnee
 
Caudal fin is homocercàl.
 
Ex: 1. Hilsa hisha (Herrings), 2. Salmon.
 
hilsa Herrings1 thumb16
 
salmon fish thumb36
 
2. Order Cypriniformes
 
Weberian ossicles connecting the ear with air bladder is present. Mr-bladder is connected with duct to the alimentary canal
 
Ex: Carps. (Labeo, Cinhina, Barbus).
 
3. Order Anguilllformes
 
Body eel like, air-bladder, If present connected with intestine by a duct.
 
Ex: Anguilla.
 
4. Order Beloniformes
 
Physoclistic fishes in which fins are without spines.
 
Ex: Exocoetus (flying fish), Cypsilurus
 
5. Order Syngnathlformes
 
Physoclistic fishes in which the first dorsal fin, if present, is spinous.
 
Ex: Hippocampus (Sea horse), Syngnathus (Pipe-fish)
 
6. Order Syinbranehiformes
 
Eel like body, air-bladder is absent spines absent In fins.
 
Ex: Asnphinuous.
 
7. Order Psrciformes
 
Physoclistic fishes fins usually with spines. Usually two dorsal fins.
 
Eg: Fierasfer, Anabas (Climbing perch).
 
8. Order Pleuronectiformes
 
Both eyes are situated on one side skull is asymmetilcal. Fins usually without spine. Adults without air bladder.
 
Ex: Cynogiossus
 
9. Order Echenelformes
 
The spinous dorsal fin is t into an adhesive disc placed on the head. Air bladder is absent.
 
Ex: Echenis (Sucker fish).
 
10. Order Ophiocephaliformes
 
Physoclisfic fishes in which are Without spine, scales are cycloid, air bladder is very long.
 
Ex: Channa or opiocephalus.
 
11. Order Tefradontiformes
 
Gill openings restricted air bladder is present or absent.
 
Ex: Tetrodon, Diodon (Porcupine fish).
 
12. Order Gadiformes
 
Physoclistic fishes in which fins are without spines, scales cycloid.
 
Ex: Gadus (cod).
 
Gadus cod fish thumb13

GENERAL CHARACTERS OF FISHES (PIECES)

Written by Friday, 30 June 2017 00:12
Fishes are first evolved in silurian period of palaeozoic era. They increased their number in Devonian period. Devonian Period is Called Age of Fishes.
 
Fishes are first jawed vertebrates. They live in water. They are cold blooded vertebrates.
 
CHARACTERS
 
  1. Fishes are aquatic; cold blooded vertebrates.
  2. Their body is divisible into head, trunk and tail. Neck is absent.
  3. It has a spindle shaped body. It is helpful in swimming.
  4. The body is covered by scales. They are placoid scales, cycloid scales, ctenoid scales, ganoid scales etc.
  5. Respiration is by gills. Gills are the extensions of the pharynx. In the elasmobranches fishes, the gills will open separate. In bony fishes the gill slits are covered by operculum.
  6. On the head a pair of nostrils are present internal nostril are absent. In Dipnoi Internal nostrils are present
  7. On the head a pair of eyes is present.
  8. On the lateral sides of the body LATERAL LINE SENSE organs are present. They detect the pressure changes of water.
  9. The body shows paired and unpaired fins. Pelvic and pectoral fins are paired. Dorsal and ventral fins are unpaired. They maintain balance in water. They are useful for locomotion.
  10. The digestive system is well developed. In the intestine of shark scroll valve Is present. The nervous system contains brain and spinal cord. Brain is small & it will not occupy the entire cranial cavity.
  11. 10 pairs of cranial nerves are present.
  12. Kidneys are mesonephrlc.
  13. Urinary bladder is absent
  14. The skeleton of some fishes is made by cartilage. They are called cartilage fishes. In some fishes the skeleton is made by bone. They are called bony fishes.
  15. In some fresh water fishes accessory respiratory organs are present. They will take up aerial respiration.
  16. Sexes are separate. In male sharks claspers are present.
  17. Many fishes are oviparous. Some fishes are viviparous.
  18. In the development of fishes amnion is not developed. Hence these animals are called anamniotes.

AMMOCOETES LARVA

Written by Wednesday, 28 June 2017 17:35
Ammocoetes Larvae: Matamorphosis
 
In the life history of Petromyzon a larval form is seen. It is called Ammocoetes larva.
 
  • Ammocoetes larva is transparent and 1 cm., in length.
  • Ammocoetes larva lives in U shaped burrows of mud.
  • Ammocoetes larva comes out of the burrow at night only to change its feeding ground, then it buries again.
  • Ammocoetes larva has an eel like body and it differs from the adult In several characters.

    ammocoetes larvae thumb14

  • It has no buccal funnel.
  • Around the mouth a semi circular oral hood is present
  • Below the mouth short transverse lower lip is present and it has no teeth.
  • Paired eyes are covered by thick skin.
  • Behind the buccal tentacles, a velum with a pair of cup-shaped muscular flaps are seen.
  • Surrounding the mouth buccal tentacles are present.
  • The pharynx is associated with seven pairs of gill pouches.
  • The pharynx is continued into the oesophagus posterioily.
  • The endostyle is present on the ventral side of the pharynx.
  • The mucus secreted by the endostyle passes into the peripharyngeal grooves of the pharynx.
  • Food particles like unicellular algage, bacteria which enter with the incurrent of water and entangled with the mucous. Thus the food associated with mucous carried into the oesophagus from the pharynx. Because of muscular movement of velum and pharynx, the ammocoetes larvae feeds.

Metamorphosis of Ammocoetes Larva
 
  • After a long period of larval life, the Ammocoetes larva metamorphoses into the adult.
  • The endostyle modifies into the thyroid gland.
  • The oral hood changes into the buccal funnel with horny teeth,tongue and a round mouth.
  • Paired eyes are developed completely.
  • The velum degenerates by leaving a rudiment.
  • The continuous dorsal fin breaks into dorsal and a single caudal fin.
  • The young lamprey migrates to the open sea from rives and becomes carnivorous adult animals.
 
The ammocoetes larva exhibits striking similarities with Amphioxus. it is a very primitive and generalised vertebrate. It may be regarded as the connection link between Amphioxus and cyclostomes.

BRANCHIAL BASKET OF PETROMYZON

Written by Wednesday, 28 June 2017 17:24
Branchial Basket
 
In Petromyzon the visceral skeleton contains branchial basket. It lies external to the gill pouches. It shows 9 irregular vertical bars and 4 longitudinal bars on either side. The first vertical bar lies just behind the styloid cartilage. The second is in front of the first gill slit. The remaining seven vertical bars are behind the 7 gill slits. The last vertical bar Is joined to a cup like pericardial cartilage. It supports the posterior and lateral walls of the pericardium. The longitu1nal bars are called subchordal, epitrematic, hypotrematic and median ventral. The subchordal bar runs along the notochord. Ft is joined to the cranium In front. The epitrematic and hypotrematic bars lie above and below the gill slits. The median ventral bar is placed in the midventral line and partly fused with the corresponding bone of the other side.
 
Functions of Branchial Basket
 
In Petromyzon branchial basket give support to the gills. It will keep the gill slits open throughout.
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