Phylum Chordata

This phylum is characterized by three unique features, at least during the early stages of their development.

• A rod like structure called notochord lying above the digestive tract.

• A tubular nerve cord lying above the notochord.

• A pair of gill slits in the pharangeal region.

Only the nerve cord persists throughout the life of the organism. The notochord is usually replaced by a vertebral column and the gill slits disappear during the embryonic stage. Phyllum chordata is divided into three subphyla

• Sub phylum urochordata.

• Sub phylum cephalochordata.

Sub phylum Urochordata

Pyrosoma

• Marine in habitat.

• Notochord is found in the tail in the larval form. Hollow nerve cord is also present in the larva.

• Body is covered by a tunic.

• Phyarynx has several gill slits.

Example:

Herdmania, Doliolum, Pyrosoma

Sub phylum cephalochordata

Brachiostoma

• Headless, tiny fish-like chordates.

• Notochord, nerve cord without a distinct brain, gill slits and a port anal tail present.

Example:

Branchiostoma (Amphioxus)

Subphylum vertebrata

• This includes the majority of chordates.

• Head is prominent.

• Nervous system and exoskeleton are highly developed.

• Notochord is replaced by a jointed vertebral column.

• Two pairs of appendages (limbs).

• Aquatic animals have gills.

Subphylum vertebrata is sub divided into seven classes

• Cyclostomata

• Chondrichthyes

• Osteichthyes

• Amphibia

• Reptilia

• Aves

• Mammalia

Class cyclostomata

Petromyzon (lamprey)

• Very primitive vertebrates.

• Do not have jaws. Being ectoparasites, mouth is of the sucking type with the help of which they stick to the host.

• Notochord present.

• Respiration is by gills enclosed in pouches.

• Heart has two chambers.

• Is cold blooded.

• Gonad is single and fertilization is external.

Example:

Petromyzon (Lamprey)

Class chondrichthyes (cartilaginous fish)

Scoliodon

• Large marine organisms.

• Body is flat, disc shaped or spindle shaped.

• Body is covered with placoid scales.

• Skeleton is cartilaginous.

• Respiration is through gills.

• Heart is two chambered.

Example:

Scoliodon (Indian shark), Torpedo (electric ray), Trygon (sting ray)

Class Osteichthyes (bony fish)

Labeo rohita (rohu)

• Found in lakes, rivers and seas.

• Spindle shaped body covered with cycloid or tenoid scales.

• Mouth is anterior.

• Skeleton is partly or completely bony.

• Gills are filamentous.

• Heart is two chambered.

Example:

Labeo (carp), Exocoetus (flying fish), Hippocampus (sea horse),

Anabas (climbing perch), Protopterus (lung fish)

Class amphibia

Dendrobates

• Live in both water and on land.

• Respiration is by gills, lungs or skin.

• 3 chambered heart.

• Is cold blooded.

• Have two pairs of pentadactyl (5 digit) limbs which may be absent in some cases.

Example:

Rana (frog), Bufo (toad), Hyla (tree frog), Necturus

Class Reptilia (creeping vertebrates)

Flying lizard (Draco)

• Mostly terrestrial.

• Heart is 3 chambered, is cold blooded.

• Breathe through lungs.

• Body covered with scales.

• Have two pairs of pentadactyl (five digit) limbs which are absent in snakes.

Example:

Hemidactylus (wall lizard), chameleon, Draco (flying lizard)

Class Aves (birds)

Sparrow

• Arboreal in habitat i.e, they live on trees.

• Warm blooded. 4 chambered heart.

• Body covered with feathers.

• Lungs have membranous extensions called air sacs to make the body light.

• Mouth is surrounded by a beak. Teeth are absent.

• Fore-limbs are modified into wings.

Class mammalia (mammals)

Chimpanzee

• Most intelligent of all organisms.

• Warm blooded with 4 chambered heart.

• Give birth to young ones.

• The mother suckles her young ones on milk secreted by special glands called mammary glands.

• Body covered with hair.

• Have two pairs of pentadactyl limbs.

• Breathe through lungs.