Chordates up to class level

Phylum : Chordata

• Phylum chordata are characterised by the presence of a notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits.
• These are bilaterally symmetrical, triploblastic coelomate with organ system level organization. They posses post anal tail and a closed circulatory system.
• Phylum chordata is divided into 3 subphylum; urochordata, cephalochordata and vertebrata.
• Urochordata and cephalochordata are referred as protochordata and they are exclusively marine animals.
• In urochordata (tunicate) notochord is present only in the larval tail and disappears in adult.
• Larva (ascidian tadpole) undergoes retrogressive metamorphosis (change from better developed larva to less developed adult)
• Examples:
  i) Herdmania (Sea squirt)
  ii) Ascidia
  iii) Salpa
  iv) Doliolum
• In cephalochordata, notochord extends upto anterior end of the body and present through out the life. Pharyngeal gill slits are numerous in number and are better developed.
• Example: branchiostoma (amphioxus lancelet)
• Vertebrata are advanced chordates that have cranium around brain. It posses notochord during embryonic period. Laver it is replaced by vertebral column (back bone in adults)
• They have ventral muscular heart with 2/3/4 chambers, kidneys for excretion and osmosegulation and paired appendages which may be tins / limbs.
• Jawless vertebrates (agnatha) are most primitive of all craniates. Mouth doesn't posses jaws. They don't have paired appendages. They are cold blooded which existing in class named cyclostomata.
• 
• Class cyclostomata (circular mouth) have 6-15 pairs of gilt slits for respiration. Body is eel like tail is compressed, skin is smooth without scales and tins.
• They are marine but migrate for spawning to freshwater. Their larvae after metamorphosis return to ocean cranium and vertebral column are cartilaginous.
• The heart is two chambered. Circulation is closed type kidney is mesonephric. 8-10 pairs of cranial nerves are present. Fertilization is external. Larva is ammocoetes.
• Examples:
  Petromyzon (Lamprey)
  Myxine (Hagfish)
  Class Chondrichthyes (Cartilaginous fish)
• Mostly marine bears cartilaginous endoskeleton exoskeleton consists of placoid scales which are dermal in origin.
• They have 5-7 pairs of lamelliform gills. Gills are not covered by opercula except chimaera. Heart is 2 chambered, kidneys are mesonephric, uricotelic.
• Mouth is centrally placed. 4 spiral valve named scroll valve is present in intestine. Digestive tract leads to cloaca.
• Only inner ear is present, have 3 semicircular ducts, lateral line sense organs are well developed. Kidneys are mesonephric (urea is nitrogenous waste).
• Sexes are distinguishable externally. Fertilization is internal and many of them are viviparous. Some have electric organs (eg: Trygon). They are cold blooded (poikilothermous)
• Examples:
  1. Scoliodon (dog fish)
  2. Pristis (saw fish)
  3. Carcharodon (great white shark)
  4. Trygon (sting ray)
  5. Torpedo (electric ray)
  Class osteichthyes (Bony fishes)
• Osteichthyes includes all members of lung fishes and are both fresh and marine water fishes. Body has three regions, head, trunk and tail. Tail is homocercal.
• Scales of 3 types: ganoid, cycloid, ctenoid. Placoid scales are absent. Mouth is horminal, digestive tract leads to anus. Cloaca is absent in bony fishes.
• Swim/air bladder is present which facilitates floating and may function as respiratory organ gills are 4 pairs and covered by opernaculum.
• Heart is 2 chambered sinus venosus and conus arteriosus is present kidney is mesonephric. (ammonotelic/ureotelic)
• 10 pairs of cranial nerves are present. Well developed lateral line system is present.
• Sexes are separate, fertilization is external mostly oviparous and development is direct.
  Examples:
  Marine - exocoetus (flying fish) can glide in air
              Hippocampus (sea horse) the male has breed pouch.
  Freshwater : Labeo (Rohu), Catla (Katla)
  Aquarium   : Betta (fighting fish)
                     Pterophyllum (Angel fish)
                     Gambusia is predatory of mosquito larvae.
  Class Amphibia (two life)
• They are cold blooded, amphibious in nature present without scales, oviparous, vertebrates, Head distinct, trunk elongated. Neck and tail may present / absent.
• Skull is dicondylic, brain is poorly developed. Cranial nerves (co pairs) are present. Limbs usually 2 pairs (tetra pod) some limbless.
• Pigment cells (chromatophores) are present, exoskeleton is absent, endoskeleton mostly bony. Notochord doesn't persist.
• Heart is three chambed (2 auricles + 1 ventricle) sinus venosus is present. Kidneys are mesonephric (uricotelic)
• Ear consist of middle and inner ear. Tympanum covers middle ear which has single ossicle called columella auris.
• Sexes are separate. Fertilization - external, females are oviparous. Development is indirect. Amphibians are only fresh water animals, not found in sea.
• Examples:
  1. Bufo (Toad)
  2. Rata (frog)
  3. Hyen (Tree frog)
  4. Salamander (salamander)
  5. Ichthyophis (Limbless amphibian)

Class reptilia

• First Class of vertebrates which has dry horny scales or scutes covered skin. This class name refers to the mode of cocomotion. Study of reptiles are called as herpetology.
• They are terrestrial, creeping / burrowing oriparous, cold blooded, tetrapodal vertebrates. Limbs are two pairs, and pentadactyl. (limbs are absent in few lizards and all snakes)
• Mouth is terminal bearing conical teeth - pleurodont in lizard and snake, thecodont in crocodiles. Teeth are absent / replaced in turtles.
• Endoskeleton is bony. Skull is monocondylic alimentary canal terminates into cloacal apertune. Two systemic arches are present.
• Heart is 3 chambered (usually), except cnecodile (4 chambered). Respiration by lungs throughout life. Kidneys are metanephric (uricotelic). Cranial nerves are 12 pairs.
• Jacobson's organ (vomeronasal organ) is present on roof of mouth act as olfactory (smell) organ. It is well developed in snake and lizard.
• Sexes are separate, male has copulatory organ fertilization is internal mostly oviparous, embryonic membrane appears during development. No metamorphosis, parental care is absent.
• Examples:
  Calotes (Garden lizard)
  Hemidactylus (wall lizard)
  Chelone (Turtle)
  Testudo (Tortoise)
  Naja (Cobra)
  Bungarus (Krait)

Class Aves

• Birds are feathered bipeds, air breathing, freely flying warm blooded vertebrates often they are described as "glorified reptiles".
• Body is boat shaped and streamlined. It is divisible into head, neck, trunk and tail. Bean is present which lacks teeth.
• Limbs are two pairs, forelimbs are modified as wings for flying. Hind limbs / legs are large and adapted for walking, wading, hopping and swimming.
• Legs bear horny epidermal scales. Skin is dry without any glands. Only cutaneous gland is uropygial or preen gland at the base of the tail. Sweat glands are absent. Oil/preen glands are absent in ostrich and parrot.
• Endoskeleton is bony but delicate and light. Bones are pneumatic / hollow and have no marrow. The largest and most powerful muscle is pectoralis major.
• Skull is monocondylic. The last 3/4 fused tail vertebrate form a structure called pygostyle. Synsacrum is formed by fusion of posterior thoracic, lumbar, sacral and anterior caudal vertebrae.
• The forked bone furcula formed by fusion of two chlorides and inner clavicle is called wishbone.
• Alimentary canal contains crop for storing and softening food. Gizzard is for cuisine, food. Respiration takes place in lungs, which contains of major air act.
• Voice box lies at the junction of trachea and bronchi is called as syntax. Larynx is without vocal cord.
• Heart is completely 4 chambered. Sinus venosus is absent. Only right aortic arch is present in adults renal portal system is vestigial.
• Kidneys are metanephric excretion is uricotelic. Urinary bladder is absent. Cranial nerves are 12 pairs middle ear contains single ossicle.
• Eyes posses nictitating membrane. Pecten present in this helps in the nutrition of eye ball. It is found in all birds except kiwi.
• Sexes are separate. All are oripavous with only single functional ovar and oviduct (mullerian duct). Development is direct birds are homeotherms.
• Examples:
  Corvus (crew)
  Psittacula (Parrot)
  Paro (Peacock)
  Neophron (rupture)

Class Mammalia

• They are terrestrial warm blooded animals. Some have gone back to water eg: whales. Occur is all sorts of habitats. Skin is glandular and covered with epidermal hair.
  Glands
  Sudorfic glands → Sweat
  Sebaceous glands → Oil
• There are two pairs of pentadactyl limbs which helps for doing various activites endoskeleton is bony, mouth is small. Buccal cavity has true salivary glands. Teeth occur in both jaws.
• External ear/pinna with an external auditory meatus inner and middle ear present. Respiration occurs by lungs. Heart is 4 chambered (2 auricles, 2 ventricles)
• Fertilization is internal sexes are often distinguishable except egg layering monotreme, mammals are viviparous. Development is direct. Body temperature is regulated (Homeothermy)
• Examples: Oviparous - Ornithorhynchus (platypus) Viviparous Macaca (Monkey), Equus (Horse), Elephants, Felis (Cat), Panthera leo (Lion), Pteropus (flying fox) etc.