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Phylum Chordata
1. Chordates possess 4 characters at least once during their life time (in embryo or larva or adult):
a) Notochord – an elastic chord, is replaced by vertebrae in most chordates called Vertebrates
b) Dorsal and hollow nerve tube – develops into brain and spinal cord in vertebrates
c) Pharyngeal Gill Clefts or pouches – are slit like openings in sides of pharynx and help in respiration in lower
chordates.
d) Post-anal Tail – is present in all chordates.
Urochordate – Sea Squirt
Cephalochordate – Amphioxus
Vertebrates –fishmammal
Notochord and nerve tube in
tail of larva. Uro = tail
Notochord extends into
anterior end. Cephalo = head
Notochord of embryo or larva
replaced by vertebrae
Body covered by test with
spicules. No head or eyes.
Fish like body has no head.
Distinct head, eyes, fins or
limbs
Fixed to sea rocks
Burrowed or free swimming
Free swimming
Filter feeder
Filter feeder
Mostly Predators or herbivores
2. Vertebrates have jawless fishes Cyclostomes or Agnatha and Gnathostomates the vertebrates with jaws in mouth.
3. Agnatha – Cyclostomes are jawless fishes only having unpaired fins. The circular mouth act as a sucker a rasping
tongue helps in feeding. Lamprey is an ectoparasite of sharks. Hag fish is slimy and usually enters dead or dying
animals and feeds on the soft viscera. Cyclostomes lack jaws and paired fins/limbs of other vertebrates.
4. Gnathostomates include fishes – animals with paired fins and Tetrapods – animals with 2 pairs of limbs. Fishes live in
water, respire with gills, skin covered with scales, have 2 chambered heart both paired and unpaired fins. Fishes
have 2 main classes Cartilaginous fishes and Bony fishes.
Fish Class 
Chondrichthyes=cartilaginous fishes
Osteichthyes = bony fishes
Position of mouth
Ventral, below the snout
terminal
Pharyngeal gill-slits
Exposed and easily seen
Covered by gill cover
Scales
Indistinct, small
Distinct, large
Tail fin
Lobes asymmetrical
Lobes symmetrical or unlobed
Swim bladder – to
regulate buoyancy
absent
Present in many fishes, helps to gain
or lose depth in water
For example
Sharks and rays
Salmon, Tuna, and gold fish
5. Amphibians (amphi = both, bios = living, can breathe in air as well as water) are naked vertebrates lacking
scales/feathers / hair. They use skin as respiratory organ and developed lungs. Amphibians moved freely on land but
have to return to water to release eggs. Fertilization is external and eggs hatch to form larva. The larva is the 1st
feeding stage and is fish like having gills. It undergoes metamorphosis to become adult amphibian. Frog  Egg
tadpole larva  Frog. For example Frogs, Toads, Salamanders, and mud puppies.
Class 
Fishes
Amphibians
Reptiles
Aves = birds
Mammals
Skin cover
scales
absent
scales
feathers
hair
heart
2 chambered
3 chambered
3 chambers
4 chambered
4 chambered
Respiration by
gills
Skin, lungs
lungs
lungs
lungs
2 pairs of
fins
legs
legs
legs
legs
Teeth used for
Holding food
holding
holding
Absent replaced
by bill or beak
Chewing food
ears
absent
Ear drum at
skin level
Ear drum in
Ear canal
Ear drum in Ear
canal
Pinna outside
ear canal
Eggs
Need water
Need water
Laid on land
Laid on land
Give birth
6. Reptiles developed the amniotic egg and became 1st true land vertebrates. Amnion is a fluid filled sac and protects
embryo from desiccation (drying up) on land. This eliminated the need of external water, like amphibians, for
fertilization. They have scales on skin to prevent water loss, and also have claws on digits and a 3-chambered heart.
Eggs with lot of yolk and hatch into adults. No larval stage present. Reptiles include turtles, lizards, snakes, alligators
and crocodiles. Dinosaurs, the most famous extinct animals, belonged to reptiles. Birds evolved as a direct line from
dinosaurs.
7. Birds are endotherms and maintain high body temperature and can live in extreme cold climates like Antarctica. The
bones are very light but strong. Body has feathers and wings. Feet are covered with scales to indicate close
relationship to reptiles. Birds also lay amniotic eggs with large yolk and no larva needed. Due to marked parental
care for the eggs and hatchlings most birds lay only 2-3 eggs. The evolution of beak or bill helped them to specialize
for different kinds of food. Sternum developed a high flat vertical bone, keel, to accommodate bulky flight muscles.
Lungs are supported by air sacs to get oxygen even during expiration (breathing out). Due to brilliance of colors
Huxley called them ‘Glorified Reptiles’.
8. Mammals – body covered by hair, mammary glands to feed milk, specialized teeth (incisiors for cutting; canines for
tearing; premolars and molars for chewing), ear canal covered with Pinna = auricle, and 7 vertebrae in neck.
9. Mammals include egg laying mammals, marsupials and placental mammals.
10. Monotremes = the egg laying (Oviparous) mammal – live only in Australia, lay eggs and feed hatchlings with milk.
Duck bill platypus and spiny ant eater are only 2 examples. They are the connecting link between early reptiles and
mammals.
11. Marsupials live only in Australian and South American regions. They give birth Viviparous) to premature babies and
many carry them in an abdominal pouch = marsupium. Mammary glands are present in the pouch. Well known
examples are Kangaroo, Koala and Opossum.
12. Placental Mammals – are most successful and most evolved animals including humans. Give birth (viviparous) to
mature babies. Endotherms – maintain body temperature. Most live on land. Aquatic mammals include Whales,
dolphins, seals etc and flying mammals are bats. In viviparous animals developing embryo draws nutrition and
oxygen from mother’s blood and pass out wastes to it. Bear is omnivore but lion, tiger, wolf, cat and dog are
carnivore mammals. Cattle, deer, zebra , and giraffe are grazing animals. Monkeys, apes and humans are primate
mammals.