Phylum- Chordata

Phylum- Chordata :

• Have supporting notochord in their body. 
• All chordates are included in the same phylum. 
• The phylum Chordata is classified in to three subphyla. 

Important characters of phylum Chordata :

• Notochord is present - during at least any developmental stage.
• Pharyngeal gill slits are present - during at least any developmental stage. 
• Single, tubular spinal cord is present on dorsal side of body. 
• Heart is present on ventral side. 

A. Sub phylum - Urochordata 

• Marine animals.
• Body is covered by skin-like test or tunic. 
• Larvae of these animals are freely swimming and notochord is present in only tail region of larvae. 
• Larvae metamorphose into adults after settling down at bottom of the sea. 
• Hermaphrodite. 
• Examples: Herdmania, Doliolum, Oikopleura, etc.

B. Sub phylum -Cephalochordata

• Small, fish-like, marine animals. 
• Notochord is present throughout the body length.
• Pharynx is very large and contains gill-slits.
• Unisexual.
• Ex.: Amphioxus.

C. Sub phylum -Vertebrata/Craniata

• Notochord is replaced by vertebral column.
• Head is well developed.
• Brain is protected by cranium.
• Endoskeleton is either cartilaginous or bony.
• Jaw-less chordates - Agnatha
• Chordates with jaws - Gnathostomata.

Subphylum- Vertebrata is divided into six classes as follows-

a. Class- Cyclostomata :

• Jaw-less mouth provided with sucker. 
• Skin is soft and without any scale.
• Paired appendages are absent.
• Endoskeleton is cartilaginous.
• Most - ectoparasites.
• Examples: Petromyzon, Myxine, etc. 

b. Class- Pisces

• Cold blooded (Poikilotherms) aquatic animals.
• Body is spindle shaped to minimize water-resistance.
• Paired & un-paired fins for swimming. 
• Tail fin is useful as a steering organ during swimming.
• Exoskeleton - scales & endoskeleton - either cartilaginous or bony.
• Respiration - gills.
• Examples.: Rohu, Pomfret, Sea  horse, Shark, Electric ray, Sting ray, etc.

c. Class- Amphibia :

• Strictly aquatic during larval life.
• Perform only aquatic respiration in water 
• On land during adult life  perform aquatic as well as aerial respiration. 
• Have two pairs of appendages. 
• Digits are without claws.
• Exoskeleton is absent. 
• Skin usually kept moist for respiration.
• External ear is absent but tympanum is present.
• Neck is absent. 
• Eyes are prominent with eye lids.
• Ex.: Frog, Toad, Salamander, etc.

d. Class- Reptilia :

• First true terrestrial animals with creeping movement.
• Cold blooded (poikilotherms).
• Skin is dry and scaly.
• Neck is present between head & trunk.
• External ear is absent. 
• Digits are provided with claws.
• Examples: Tortoise, Lizard, Snake, etc.

e. Class- Aves : 

• Completely adapted for aerial life.
• Warm blooded (Homeotherms) i.e. they can maintain their body temperature constant.
• Body is spindle-shaped to minimize air resistance during flight.
• Forelimbs are modified into wings. 
• Digits are covered with scales and bear claws.
• Exoskeleton -feathers.
• Neck is present.
• Jaws are modified into beak.
• Examples: Peacock, Parrot, Pigeon, Duck, Penguin, etc.

f. Class- Mammalia : 

• Presence of mammary glands is typical character of mammalia.
• Warm blooded.
• Body is divided into head, neck, trunk and tail.
• Digits are provided with nails, claws, or hooves.
• Exoskeleton - hairs or fur.
• Examples: Elephant, Human, Kangaroo, Dolphin, Bat, etc.