Friday, March 12, 2010

Taxonomy of Chordates

Phylum – Chordata:
Ü Three primary chordate characters are:-
i. Presence of notochord (embryonic, larval or adult).
ii. Presence of single dorsal tubular nerve cord.
iii. Presence of paired pharyngeal clefts.
Ü Bilateral symmetry and metameric segmentation.
Ü Presence of true coelom (schizocoel in vertebrates and enterocoel in protochordates).
Ü Phylum Chordata is divided into two groups Protochordata and vertebrata.

Protochordata (Acraniata):
Ü These are primitive chordates, vertebrae and paired appendages are absent.
Ü All protochordates are marine.
Ü Protochordates are also called invertebrate chordates.
Ü On the basis of the location of notochord, protochordates are divided into three subphyla. Hemichordata, Urochordata and Cephalochordata.

Ü Notochord only in the anterior end.
Ü Notochord of these animals is not homologous to notochord of other chordates, also called as "Stomatochord".
Ü Larva of Balanoglossus is called tornaria.

Ü Commonly called 'tunicates' excusively marine.
Ü Notochord only in the tail region of larva.
Ü Retrogressive metamorphosis results in the degeneration in adult.
Ex. Herdmania, Pyrosoma: emits strongest light among marine organisms.

Ü Adult with notochord extending from head to tail, hence the name Cephalochordata.
Ü Coelon enterocoelous.
Ü Excretion by protonephridia with solenocytes.
Ü Ex. Amphioxus. (Branchiostoma).

Vertebrata (Craniata):
Ü Vertebrates are advanced chordates. They are also known as 'euchordates' or 'higher chordates'.
Ü Vertebrates are divided into two divisions:-
(i) Agnatha (ii) Gnathostomata

1. These are primitive vertebrates.
2. Without jaws and paired appendages.

Class – I Cyclostomata:- Without scales, jaws with rounded mouth and lateral fins present.
Class – II Gnathostomata:- Jaws with mouth and paired appendages. Gnathostomata can be divided into two super classes: (i) Pisces (ii) Tetrapoda.


Super Class I Pisces:- Aquatic vertebrates with fins, gills and scaly skin. Fishes are divided into three classes:
Placodermi: Extinct fishes.
Chondrichthyes: Mostly marine cartilaginous fishes, skin with placoid scales, gills not covered by operculum like Scoliodon (shark).
Osteichthyes: Freshwater and marine bony fishes, skin with cycloid, ctenoid scales etc. gills with operculum like Labeo (Rohu).

Super Class II Tetrapoda:-
Amphibia: Larva aquatic, adult typically, terrestrial, skin moist glandular, no exoskeleton, heart 3-chambered, e.g. Frog.
Reptilia: Terrestrial tetrapods, creeping skin dry covered by ectodermal scales or bony plates, heart incompletely 4-chambered, respiration by lungs, e.g. Lizards and Snakes.
Aves: Typical flying vertebrates covered with feathers, forelimbs modified into wings. No teeth in beak, Heat 4-chambered, e.g. Birds.
Mammalia: Body covered by hair, skin glandular with mammary glands which secrete milk for young. Heart 4-chambered, air breathing vertebrates, e.g., Rabbit, Man etc.
Anamniota: These are the vertebrates without amnion (and other extraembryonic membranes). Anamniota includes Pisces and Amphibia.
Amniota: These are vertebrates with amnion (and other extraembryonic membranes). Amniota includes Reptilia, Aves and Mammalia.

Study of the fishes is lychthyology. (Ichthyophis is not a fish it is an Amphibian)
Ü Pisces is the largest class of vertebrates in number of species.
Ü Fishes originated during Ordovician period of Palacozoic era.
Ü First fish evolved was Ostracoderm.
Ü Locomotion by paired pectoral and pelvic fins along with median dorsal and caudal fin.
Ü Skin is usually provided with scales. Three common types of scales are placoid, cycloid and ctenoid.
Ü Heart 2-chambered (1 auricle and 1 ventricle). It is venous heart pumping impure blood only.
Ü Sinus venosus present. Both renal portal and hepatic portal systems are found.
Ü Kidneys mesonephric. Excretion ammonotelic or ureotelic.
Ü Tympanum, tympanic cavity and ear ossicles are absent.
Ü Lateral line receptors present.
Ü Female oviparous or viviparous.
Ü Eggs large with much yolk (Macrolecithal).
Ü Fishes are cold blooded or poikilothermic animals.

Comparison of Cartilaginous and Bony Fishes

Cartilaginous Fishes Bony Fishes
Mostly marine Both marine and fresh water
Placoid scales Usually cycloid or ctenoid
Cartilaginous Mostly bony

Miscellaneous Points:
Ü Scoliodon (Shark or dogfish) is a cartilaginous fish.
Ü Ampulla of Lorenzini present in the snout of shark is a thermoreceptor.
Ü Shark is viviparous.
Ü Air bladder found in bony fish is a hydrostatic organ.
Ü Lung fishes or Dipnoi are freshwater lobed finned fishes. Lung fishes are known as uncle of Amphibian.
Ü Fishes migrate mainly for breeding (spawning). Two main types of migrations are:
Catodromous migration – Fresh water to sea, e.g. Anguilla.
Anadromous migration – Sea to fresh water, e.g. Salmon.
Ü Largest and best aquarium in India is located in Tarapur, Mumbai. Largest zoo of India located at Chennai, largest museum is located at Kolkatta, largest zoo of the world is located at Kruger (South Africa).
Ü Exocoetus (flying fish) is true fish.
Ü Remora (Echeneis) has modified dorsal fin into a sucker. It attaches to the body of sharks, whales, etc. (Commensalism).
Ü Hippocampus (Sea horse) shows parental care. On the belly of male is a brood pouch for incubating eggs.
Ü Gambusia (mosquito fish) eats on the larvae of mosquito (larvicidal fish or top minnow) so it is used in biological control of mosquito.
Ü Exotic fish eg. Cyprinus, caprio (silver carp).
Ü Torpedo (Astrape) is the electric ray. Their electric organs are highly modified masses of muscle cells.

Common Names:
Cartilaginous Fishes:
Scoliodon : Dogfish (shark)
Trygon : Sting ray
Torpedo : Electric ray
Pristis : Sawfish
Chimaera : Rat fish
Bony Fishes:
Clarius : Cat fish
Echeneis : Sucker fish
Hippocampus : Sea horse
Gambusia : Mosquito fish
Exocoetus : Flying fish
Labeo rohita : India carp
Anguilla : Freshwater eel
Oncorhynchus : Pacific salmon
False fishes:
Common Name Genus Phylum
Jellyfish Aurelia Coelenterata
Silverfish Lepisma Arthropoda
Crayfish Astacus Arthropoda
Razofish Solen Mollusca
Cuttlefish Sepia Mollusca
Devilfish Octopus Mollusca
Starfish Asterias Echinodermata
Hagfish Myxine Chordata

Ü Amphibians originated during Devonian period of palaeozoic era from Stegocephalia.
Ü Endoskeleton bony, skull dicondylic (with two occipital condyles).
Ü Heart three-chambered with two auricles and one ventricle.
Ü Sinus venosus present, both renal and hepatic portal system are well developed.
Ü Kidneys mesonephric, urinary bladder large, excretion ureotelic.
Ü Cranial nerves ten pairs.
Ü External ear absent. Middle ear with a single rod-like ossicle, columella auris and a stapedial plate.
Ü Fertilization mostly external.
Ü Female mostly oviparous.
Ü Eggs large with moderate amount of yolk (mesolecithal).
Ü Larva tadpole which metamorphoses into adult.
Ü Amphibians are cold blooded or poikilothermic animals and Anamniotes.
Stegocephalia: All extinct.

Apoda or Gymnophiona:
Ü Limbless, blind elongated worm-like burrowing dermal scales embedded in skin. E.g. Ichthyophis, Uraeotyphlus, Rhinatrema, Typhlonectes.
Ü Ichthyophis is a limbless amphibian showing parental care.
Ü Ichthyophis and found in India.

Urodela or Caudata:
Ü Commonly called as newts and salamanders. E.g. Salamandra, Necturus (mud puppy).
Ü Ambystoma is founding USA and Maxico. Larva is axolotl. It shows neoteny or paedogenesis.

Salientia or Anura:
Ü Commonly called as frogs and toads tailless without gills, e.g., Rana, Bufo, Alytes, Rhacophorus.
Ü Bufo marinus is a poisonous amphibian. In midwife toad, male is smaller without vocal sacs. Males show parental care.
Ü Frog is ureotelic.
Ü Functional kidney of frog tadpole is pronephrons.
Ü Poison gland of a toad is modified parotid gland.
Ü 'Horned Toad' (Phrynosoma) is a lizard living in desert, it is not an amphibian.
Ü Hyla is an arboreal frog, adapted for life in trees. It is green in colour. Terminal bones of digits are claw-shaped and swollen basally into glandular adhesive discs which enable them to climb tree.
Ü Batrachology is the study of frog.

Common Name:
Uraeotyphlus : Blindworm
Ichthyophis : Caecilian
Ampystoma : Tiger salamander
Amphiuma : Congo eel
Necturus : Mud puppy
Proteus : Cave salamander
Triton : Newt
Rana tigrina : Indian bull frog
Alytes : Midwife toad
Bufo melanostictus : Indian toad
Hyla : Tree frog
Rhacophorus : Flying frog

Ü Herpetology is the study of reptiles. Greek Herpeton, reptile.
Ü Reptiles originated during Carboniferous period of Palaeozoic era.
Ü The first reptiles are called 'stem reptiles' or 'Cotylosaurs' the genus being Seymouria.
Ü Mesozoic era is called the 'Golden Age of Reptiles'.
Ü Exoskeleton of horny epidermal scales, shields, plates and scutes.
Ü Conical teeth, pleurodont in lizards and snakes, theodont in crocodiles. Teeth are absent and replaced by horny beaks in turtles.
Ü Alimentary canal terminates into a cloacal aperture.
Ü Endoskeleton bony, skull monocondylic (with one occipital condyle).
Ü T-shaped interclavicle present.
Ü Heart is usually 3-chambered or partially 4-chambered. Interventricular septum incomplete. Heart 4-chambered in crocodiles.
Ü Kidneys are metanephric. Excretion uricotelic.
Ü Cranial nerves 12 pairs.
Ü Jacobson's organ (vomeronasal organs) in the rood of buccal cavity concerned with smell, well developed in snakes and lizards.
Ü Female are mostly oviparous.
Ü Eggs are cleidoic, eggs covered with leathery shells.
Ü Fertilization internal.
Ü Eggs macrolecithal (amount), telolecithal (distribution) of yolk.
Ü Cleavage meroblastic, extraembryonic membranes are present (Amniota).
Ü Development direct, no metamorphosis and no parental care.
Ü Reptiles are cold blooded or polkilothermic animals.

Ü Primitive reptiles with a solid skull roof.
Order I Chelonia:
Ü Commonly called turtles (marine), tortoises (terrestrial) and terrapins (edible freshwater).
Ü Certain aquatic turtles perform cloacal respiration, but all other reptiles respire with lungs.
Ü The giant land tortoise, Testudo abingdoni of Galapagos Islands is the largest chelone, 100 kg wt. life span 200-400 years.
Order II Rhychocephalia:
Ü All are extinct except a living species Sphenodon.
Ü Sphenodon is "Tautara" of New Zealand, it is a living fossil and going to become extinct.
Ü An interesting feature of Sphenodon is the presence of pineal or parietal or third eye.
Ü Sphenodon is referred to a "living fossil" because it has retained many primitive characteristics of fossil or stem reptiles.
Order III Squamata:
Ü Commonly called lizards and snakes.
Ü Saurology is the study of lizards.
Ü Serpentology or ophilology is the study of snakes.
Ü Most lizards are oviparous, two viviparous lizards are Phrynosoma and Chameleon.
Ü Draco is lizard which glide with the help of patagium, it is called 'flying dragon'.
Ü Heloderma (Gila monster) is the poisonous lizard in the world.
Ü The glass snake Ophisaurus derives its name from its ability to break off its tail when seized.
Ü The largest living lizard in the world is the ferocious dragon, Varanus.
Ü Python and Boa have vestigial pelvic girdle and hindlimbs.
Ü Snake has long, slender and bifid tongue which is sensitive to both odours and vibrations.
Ü Snakes shed scaly epidermis of skin periodically usually in one piece. This process is termed moulting or ecdysis.
Ü Python is the largest nonpoisonous snake.
Ü Common poisonous snakes are cobras, kraits, vipers, sea snakes and coral snakes.
Ü The poison injection fangs (teeth) are maxillary teeth located on maxilla.
Ü Snake poison is a mixture of enzymes and specific toxins and is a good digestive juice. It is fatal only when mixed in blood.
Ü Neurotoxins cause death by paralysis of respiratory muscles and asphyxiation.
Ü Haemotoxins are typical of vipers. They cause tissue destruction and widespread haemorrhage.
Ü Proteolysin is present in the venom of viper.
Ü The best medicine to treat snake bite is an antivenin or antivenom serum.
Ü An antivenin is prepared by injecting a horse with gradually increasing doses of a snakes venom until the horse becomes fully immunized. Blood serum of horse is collected and preserved.
Ü Kraits are dangerously poisonous because bite inject a very large quantity of poison (three times more than Cobra).
Ü A viper can be easily identified by its triangular, pear-shaped head bearing small cephalic scales.
Ü One of the largest and deadliest venomous snake is the king cobra Naja Hannah, lives in the forest area, 4 metres length, feeds on monitor lizards and other snakes.
Ü Sea snakes are poisonous; two common sea snakes are Hydrophis.
Ü Sea snakes look eel-like with laterally composed flat tails suited for swimming
Ü Sea snakes and vipers are viviparous.
Ü Pit vipers differ from true or pitless vipers is having a loreal pit between the eye and nostril on either side. Loreal pit is a thermoreceptor.

Order IV Crocodilia:
Ü Commonly called crocodiles, alligators and gavials.
Ü Teeth numerous, thecodont, lodged in sockets.
Ü Only reptile in which heart is completely 4-chambered.
Ü The lung cavity of crocodile is separated from rest of body cavity by a muscular diaphragm, analogous to that of mammals.
Ü Pineal gland is absent in crocodiles.
Ü Gavial or gharial, Gavialis gangeticus is found only in India. It lives in Ganges and Brahmputra rivers and grow to 8 metres.
Ü Dinosaurs originated along primitive mammals during Triassic period of Mesozoic era.
Ü Dinosaurs became extinct cretaceous period of Mesozoic era.
Ü Mesozoic is also called 'Golden Age of Dinosaurs".
Common Name:
Testudo : Tortoise
Trionyx : Turtle
Sphenodon : Tuatara
Hemidactylus : Wall/house lizard
Draco : Flying dragon
Phrynosoma : "Horned toad"
Varanus : Monitor lizard
Heloderma : Gila monster-Beaded lizard
Ophisaurus : Glass snake
Snakes (Nonpoisonous)
Typhlops : Blind Snake
Tropidonatus : Pond Snake
Snakes (Poisonous)
Naja naja : Cobra
Naja Hannah : King cobra
Bungarus : Krait
Viper ruselli : Pitless viper
Ancistrodon : Pit viper
Hydrophis : Sea snake

Ü Ornithology is the study of birds.
Ü Phenology is the study of bird migration.
Ü Birds originated towards the end of Jurassic period of Mesozoic era from aerial reptiles called 'Pterosaurs'.
Ü Archaeopteryx was a primitive bird. Its fossil was discovered by Andreas Wagner from Bavaria, Germany.
Ü Archaeopteryx was a connecting link between reptiles and birds.
Ü Archaeopteryx became extinct during Cretaceous period.
Ü Birds are feathered bipeds, air breathing, truly flying vertebrates.
Ü Young called birds as master of air and Haeckel called birds as glorified reptile.
Ü Jaw bones are prolonged into toothless beak or bill.
Ü Only cutaneous gland is uropygial gland or preen gland at tail base.
Ü Skull is monocondylic like reptiles.
Ü Vertebrae are heterococlous or saddle-shaped.
Ü A synsacrum is formed by fusion of posterior thoracic, lumbar, sacral and anterior caudal vertebrae.
Ü Both clavicles and a single interclavicle fused to form a V-shaped bone called furcula or wishbone or merry-thought bone.
Ü Crop secretes 'pigeon milk' during breeding season.
Ü Stomach is divided into a glandular proventriculus and a muscular gizzard.
Ü Respiration with compact, spongy, nondistensible lungs continuous with thin walled air sacs.
Ü A sound box or syrinx producing voice, lies at or near the junction of trachea and bronchi.
Ü Heart is completely four-chambered (also in mammals).
Ü Kidneys metanephric and three-lobed. Ureters open into cloaca. Urinary bladder absent. Excretion uricotelic.
Ü Cranial nerves 12 pairs.
Ü Eyes posses nictitating membrane. Pecten is a comb-like structure found in the eyes blindspot. Pecten helps in the nutrition of eyeball.
Ü Females are oviparous with a single (left) functional ovary and oviduct (Mullerian duct).
Ü Eggs of birds are cleidoic (with calcareous shell), macrolecithal (amount of yolk), telolecithal (distribution of yolk).
Ü Cleavage discoidal and meroblastic.
Ü Extraembryonin membranes present (Amniota).
Ü Feathers are found only in birds. Feathers are made up of protein Keratin.
Ü Quill feathers in the wings are called 'remiges'.
Ü Quill feathers in the tail are called 'rectrices'.

Archaeornithes: All extinct.

Neornithes: Modern as well as extinct post-Jurassic birds.

Flightless Birds:
Common Name Distribution
African ostrich Africa and Arabia
Rhea South America
Cassowary Australia and New Guniea
Emu Australia
Kiwi New Zealand
Ü African ostrich is the largest living bird. They are polygamous as one male attends several females.
Ü Egg of ostrich weight nearly 1.5 kg and requires about 50 minutes to boil it. It is the largest egg among the animals.
Ü Ostriches are easily domesticated.
Ü Kiwi is the smallest living flightless bird.

Some Important Birds:
Ü Dodo is a recently extinct bird from Mauritius. It became extinct during 17th century.
Ü Humming bird (Sunbird) is the smallest bird found in Cuba.
Ü Humming bird is a bird which can fly backwards.
Ü Wagtail is a famous migratory bird of India. It comes to India from Siberia.
Ü Cuckoo is the bird which lays eggs in the nest of other birds.
Ü Galapagos finches are associated with Charles Darwin.

Bird Sanctuaries:
Sulthanpur (Lake) Bird sanctuary, Gurgaon, Haryana.
Govind Sagar Bird sanctuary, Bilaspur, H.P.
Keoladeo Ghana Bird Sanctuary Bharatpur, Rajasthan.
Chilka Lake Bird Sanctuary Balagaon, Orissa.

Ü Mammology or Therology is the study of mammals.
Ü Mammals are the dominated animals of Coenozoic, so this ear is known as 'age of mammals'.
Ü Mammals are hair-clad, mostly terrestrial tetrapod vertebrates.
Ü Most important character of mammals is presence of mammary glands. (modified sweat glands).
Ü Skin is richly glandular containing sweat and sebaceous glands.
Ü Presence of a muscular diaphragm separating thoracic cavity from abdominal cavity.
Ü Skull dicondylic with two occipital condyles (also in Amphihia).
Ü Each half of lower jaw with a single dentary bone.
Ü Vertebra with flat centrum called amphiplatyan or acoelous.
Ü Presence of seven cervical vertebrae.
Ü Presence of 12 pairs of ribs (also 12 pairs of cranial nerves).
Ü Absence of cloaca.
Ü Teeth heterodont, thecodont and diphydont.
Ü Larynx with vocal cords.
Ü Heart completely 4-chambered (also in birds and erocodiles).
Ü Renal portal system absent.
Ü Kidneys metanephric. Ureters open into a muscular urinary bladder. Excretion ureotelic.
Ü External ear with ear pinna. Middle ear with ossicles malleus, incus and stapes.
Ü Testes mostly in scrotal sacs for sperm development.
Ü Eggs small, microlecithal, homolecithal, without shells (non cleidoic).
Ü Mammals are viviparous, except egg-laying monotremes.
Ü Extraembryonic membranes (amnion, chorion and allantois) present (amniota).
Ü Placenta is formed by chrio-allantois.
Ü Body temperature is constant, warm blooded (homoiothermous) average temperature 38oC or 98.4oF.

Ü Prototherians are primitive mammals, egg laying mammals, oviparous mammals, reptile-like mammals, confined to Australian region.
Ü Young ones are fed on milk from mammary glands without nipples.
Ü Prototherians are connecting link between reptiles and mammals.

Order: Monotremata:- Ex. Echidna (Tachglossus) Spiny anteater found in Australia, New Guinea and Tasmanis. Ornithorhynchus, duckbilled platypus found in Australia and New Zealand.

Theria: Theria is divided into two infraclasses. Metatheria and Eutheria.

Ü Metatherians are pouched mammals young born in very immature state.
Ü Gestation short, complete development in the abdominal pouch or marsupium.
Ü Corpus callosum absent.

Order: Marsupialia: Macropus (Kangaroo) found in Australian region. Didelphis (Opossum) tree dwelling, found in America.

Ü Eutheria includes viviparous placental mammals.
Ü On the basis of characteristics like skull, teeth and limbs, eutheria is arranged into 16 orders.
Insectivora: Smallest and most primitive eutherians e.g., Talpa (Mole), Erinaceus (hedgehog).
Chiroptera: Flying capable of echolocation, a type of radar system(Sonar system or natural radar system) e.g., Pteropus (Flying fox) fruit eating, frugivorous Desodus (Vampire bat) sanguivorous.
Rodentia: Largest order of mammals in number of species, small gnawing mammals. No canines e.g., Rattus (Rat), Muss (Mouse), Fanambulus (Squirrel).
Lagomorpha: Oryctolagus (Rabbit), Lapus (Hare), Tailless.
Ü Predatory flesh-eating mammals.
Canis familiaris : Dog
Felis domestica : Cat
Panthera leo : Lion
Panthera tigris : Tiger
Aeinonyx jubatus : Cheetah
Ü In India, lions are found in Gir forests of Gujrat.
Ü Tiger is the 'National mammals of India'.
Ü Aquatic mammals, breathe by lungs, blubber or subcutaneous fat present which helps in heat conservation, skin gland absent, forelimbs modified into paddle-like flippers. Hair only on snout nostrils on the top of the head teeth often lost, even very small, bones spongy, mostly gregarious and carnivorous.
Delphinus : Common Dolphin
Platanista : Ganges Dolphin
Ü Balaenopetra musculus (the blue whale) is the largest animal ever lived. Length 35 metres, weight 150 ton, feeds in arctic and Antarctic waters on microscopic animals or plankton.
Ü Herbivorous aquatic mammals with paddle-like forelimbs, no hindlimbs, no external ears, no pinna present testes abdominal.
Eg. Rhytina : Sea cow
Ü Largest land living animals. Hairless skin (pachyderm), nose upper lip modified into proboscis.
Ü Two upper incisors modified as tusks.
Ü Ivory is obtained from the tusk of elephant. Mammoths and mastodons were extinct elephants.
Loxodonta Africana : African elephant
Elephas maximus : Indian or Asiatic elephant
Elephas cyclotis : Pigmy African elephant
Ü Odd-toed hoofed animals, incisors present in both jaws.
Ü A Mule is a hybrid between Male ass (Jack) and Female Horse.
Ü A Hinny is a Hybrid between Male Horse (Stallion) and Female ass.
Ü In India Rhinoceros are found in Kaziranga National Park Jorhat Assam.
Equus caballus : Horse
Rhinoceros unicornis : Indian rhinoceros
Rhinoceros bicornis : African rhinoceros

Ü Even toed hoofed animals, incisors and canines in upper jaw usually absent, stomach 4-chambered. All except pig ruminate or chew their cud. Many with antlers or horns.
Ü Hippopotamus is called Riverine Horse (Horse of the River) found in Nile river of tropical Africa.
Ü Camels one well adapted for desert life and they are known as ship of desert.
Ü Camels are state animal of Rajasthan province.
Hippopotamus amphibious : Hippopotamus
Giraffa camelopardalis : Giraffe
Primates: Gibbon is the smallest man like ape.
Chimpanzee is the most intelligent ape.
Macaca mulatta : Rhesun Monkey
Pan : Chimpanzee
Papio : Baboon.
Homo sapiens : Human.


  1. What information is available about the kidney function of anadromous fish such as hilsa?

  2. What information is available about the kidney function of anadromous fish such as hilsa?