Classification of Chordata

Pisces

General characteristics

• They are completely aquatic found in freshwater and marine water.
• The body is streamlined or boat-shaped and laterally compressed. It helps the fishes to swim.
• The body is covered with cycloid or placoid scales which protects from external disturbance.
• It is cold blooded or poikilothermic (body temperature is not fixed but is variable according to environment)
• Locomotion takes place by paired (pectoral and pelvic pins) and unpaired fins(dorsal, anal, and caudal fins.)
• The digestive system is well developed. It possesses mouth with two jaws and teeth. Cloaca is present in the cartilaginous fishes but absent in bony fishes.
• Respiration takes place by gills. Gills may or may not be covered by the operculum.
• The heart is two-chambered, one auricle and one ventricle. Blood is red due to hemoglobin.
• Ten pairs of cranial nerves. The lateral line is present on the lateral sides, detecting water pressure.
• Sexes are separated. Fertilization is external or internal.
• Development is direct.
• Eg; Rohu(Labeo rohita), Seahorse(Hippocampus), flying fish((exocoetus)etc.
  

  

Amphibia

General characteristics

• They are amphibious, live both in water as well as on land.
• Skin is moist, thin, smooth and glandular. It does not bear scales. It makes the surface slippery.
• They are cold blooded or poikilothermic.
• Some amphibians undergo hibernation and aestivation periods during unfavorable conditions.
• The body is cylindrical and divided into head and trunk.
• It has a triangular head and bears a pair of eyes, external nostrils and tympanum. Eyes are protected with the nictating membrane.
• Locomotion takes place by fore and hind limbs. It enables the animals to walk and jump on land and swim in water. Claws are absent. Forelimbs have 4 fingers and hind limbs have 5 fingers. Hind limbs are longer and webbed toes.
• Respiration takes place by body surface, lungs and buccal cavity. Larval forms respire through gills.'
• The heart is into three chambers, two auricles, and one ventricle. RBCs are biconvex, oval and nucleated. Sinus venous and trunchus arterioscus present.
• Excretion takes by the mesonephric kidney.
• There are 10 pairs of cranial nerves arising from the brain.
• Reproduction is unisexual, sexual dimorphism is distinct.
• Fertilization is external. Development is indirect.
• Eg; Frog, Toad, Tree frog etc.
  

  

Reptilia

General characteristics

• They are elongated, cylindrical and can walk by crawling. They are creeping animals.
• They are mostly terrestrial and some are aquatic.
• Their skin is dry, rough and non-glandular. It is covered with scales or bony plates.
• It is poikilothermic.
• The body is elongated and cylindrical. It is divisible into head, neck, trunk and tail.
• They have two pairs of pentadactyl limbs except snakes. Horny claws are present in the aquatic forms. Limbs are modified into paddles.
• The tongue is short, sticky and protrusible.
• Respiration takes place by lungs. In turtles, gas exchange takes place through the cloaca.
• The heart is incompletely divided in four-chambered heart. Sinus venosusis absent but trunchus anterioscus is present. RBCs are nucleated, biconvex and oval.
• Excretion takes place by the metanephric kidney.
• There are 12 pairs of cranial nerves arising from the brain.
• Sexes are separate. Males have copulatory organs. Fertilization is internal. They are oviparous and lay eggs on land.
• Development is direct without metamorphosis.
• Eg; wall lizard, garden lizard, green turtle etc
  

  

Aves

General characteristics

• The body is covered with feathers adapted to live in air.
• The body is streamlined. The body is divisible into head, neck, trunk and tail. Head is small and round. The neck is long and flexible. The tail is short and stumpy.
• They are warm blooded. The body temperature is constant. They regulate body temperature.
• They have two pairs of limbs. The forelimbs are modified into wings for flying. The hind limbs support the body.
• A permanent beak is present without teeth.
• Skin is dry and devoid of glands except oil or preen glands at the root of the tail.
• It is fully ossified and light. Bones are pneumatic or hollow and porous without bonemarrow.
• Respiration takes place by spongy and inelastic lungs. It consists of many air sacs.
• The heart is completely divided into four-chambered. The renal portal system is vestigial.
• Excretion takes place by the metanephric kidney. The urinary bladder is absent. They are uricotelic.
• Flight muscles are well developed.
• The brain is large. It has 12 pairs of cranial nerves.
• Sexes are separated. Sexual dimorphism is often well marked.
• Fertilization is internal, preceded by copulation and courtship.
• Example; Sparrow, pigeon.
  

  

Mammalia

General characteristics

• The body is elongated, covered with fur. They have pinnae and mammary glands.
• They live in all habitats.
• The body is divisible into head, neck, trunk and tail.
• The skin is covered with hair or fur. It possesses sweat glands and oil or sebaceous glands.
• Locomotion takes place by two pairs of pentadactyle limbs, modified for various forms.
• Respiration takes place by a pair of elastic and spongy lungs. The larynx is the vocal cord.
• The heart is completely divided into four-chambered.
• Excretion takes place by metanephric kidneys. They are ureotelic.
• The brain is highly developed having 12 pairs of cranial nerves.
• Sexes are separate.
• Fertilization is internal. They are viviparous except Prototheria.
• Development is direct without metamorphosis.
• Eg; Rabbit, Squirrel.

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fig:Mammalia