Phylum Chordata – Characteristics, Classification And Examples

Phylum Chordata is one of the classifications of Kingdom Animalia. The main feature of Chordata is the presence of a notochord, hollow nerve cord, and paired pharyngeal gill. They are bilaterally symmetric with an internal cavity for true organs.

They have an organization level cell arrangement and closed circulatory system with a tail and post. There are three subphylums – Urochordata, Cephalochordata, and Vertebrata. The first two are simple in nature when compared to complex vertebrates.

This is because vertebrates have more subclasses and features to look at. 

Classification of Phylum Chordata

The first two subphylums are marine and are protochordate. Urochordata have notochord present in the larval tail only. And Cephalochordata has notochord in the entire body. Some examples of Chordata are Ascidia, Salpa, Doliolum, and Amphioxus.

The common elements in all chordates are – a notochord, dorsal nerve cord, are triploblastic and coelomate. The vertebrates are the last classification of phylum Chordata. They have subclasses under them on the basis of different criteria like blood and metabolic activity.

Let’s look at all the subclasses in detail with some important concepts around vertebrates. 

Difference between  Chordates and Non-chordates
Chordates	Non-chordates
Presence of Notochord	Absence of Notochord
Dorsal, hollow, and single nervous system	Ventral, solid, and double nervous system
Presence of gill slits	Absence of Gill slits
Ventral Heart	Dorsal Heart
Tail is present	Tail is absent

Phylum Vertebrata

The animals under this classification have vertebral columns and internal skeleton. There is a proper distribution of muscle attachment for movement. They have a notochord during the embryonic stage. Later cartilaginous replace it in the adult phase.

All chordates are not necessarily vertebrates as some can easily fit under the other two subphylums. Most vertebrates have a muscular heart with 4 chambers, a proper excretion system, and proper limbs.

They are bilaterally symmetric and triploblastic. They also have internal cavities for true organs with complex body tissues and organs. 

Below is the flow chart of different levels of animalia kingdom:

Important Vertebrates Concepts 

Viviparous and Oviparous Animals

The reproduction process is sexual or asexual. And the birth-giving process can include laying eggs or giving natural birth to young ones. Viviparous animals give birth to young ones directly. While the oviparous animals lay eggs for the same process.

The process of metamorphosis in some organisms often leads to changed physical attributes in the young ones. Caterpillar is an example of the metamorphosis cycle.  

Warm-Blooded	Cold Blooded Animals
Most of the mammals and birds are warm-blooded animals	All the reptiles, insects, arachnids, amphibians, and fish are cold-blooded animals
Their body does not change according to the external environment.	Their body changes according to the external environment.
They can survive in different environments because of controlled body temperature	They cannot survive in different environments. For eg a mountain animal will not survive in desserts.
Their food intake is higher in order to maintain body temperature.	Their food intake is lower as it converts to body mass.
They are active in both warm and cool surrounding	They act only in a warm surrounding
Sweating helps them to remain cool like elephants use their ear to do so. Some birds migrate to warmer regions in winters. Ad mammals have fur to stay warm. They can use shivering to generate heat in cold weather.	They increase their metabolism by going to the sun. and bees or dragonflies shiver to remain warm.
The parasites and viruses can easily live on them because of warmness.	Changing temperature makes it tough for parasites to survive.

Hibernation

It is a stage in which the animals become inactive and metabolically depressed. It is common in endotherms like bears and rodents and ectotherms like snakes and turtles. This behavior is most common during harsh winter seasons.

They locate themselves in places like den, burrow, or any shelter before hibernating. Often animals go under true hibernation that makes it tough for them to wake up because of temperature drop.

Warm-blooded animals like bears hibernate in winters mostly. They live on stored food body fat with low body temperature. They usually eat a large amount of food before this. 

Class – Cyclostomata

• All the organisms are ectoparasites under this class of vertebrates. 
• They mostly live on fish’s bodies. 
• They have 6-15 gills for respiration in an elongated body. 
• Their mouth is circular for sucking without jaws. 
• They have cartilaginous vertebral columns and cranium. 
• They have scales on their body and paired fins.
• Their blood circulation system is close.
• They are aquatic animals and migrate often for freshwater to lay eggs. 
• This process is spawning and they die after laying eggs. 
• Their larvae follow metamorphosis and go back to the ocean.
• Some examples are Petromyzon and Myxine. 

Class – Pisces

• They are the fishes under this class with scales and plates.
• They are oviparous animals and use gills to respire. 
• These have a streamlined body and a muscular tail for movement.
• They are cold-blooded animals with two chambers in the heart. 
• They have two types Chondrichthyes and Osteichthyes.
• The Chondrichthyes have a cartilaginous skeleton.
• The Osteichthyes have bony skeletons.

a. Chondrichthyes

• They are marine animals that have a cartilaginous endoskeleton.
• They have a ventral mouth with a streamlined body. 
• The notochord is present in them throughout life.
• They have separate gills without a cover. 
• They have tough skin with placoid scales.
• These have very powerful jaws and are predaceous.
• They swim continuously to avoid drowning as there is no air bladder. 
• They have two chambers in their hearts and are cold-blooded.
• Some of them have electric organs and a poison sting.
• They have different sexes with internal fertilization. 
• Some examples are Scoliodon, Pristis, Trygon, etc. 

b. Osteichthyes

• Fishes from fresh and marine water with bony endoskeleton are under this subclass.
• They have a streamlined body with a terminal mouth.
• They have four pairs of gills with operculum cover on each side.
• These have cycloid scales on their skin. 
• To maintain buoyancy, they have an air bladder.
• They have two chambers in the heart and are cold-blooded animals. 
• The sexes are different from external fertilization.
• They are mostly oviparous animals with direct development.
• Some examples are flying fish, Sea horse, Angelfish, etc.

Class – Amphibia

• This class can easily survive in aquatic and terrestrial environments. 
• They have moist skin without scales and eyelids for eyes. And the ear is tympanum. 
• They have a well-developed alimentary canal, urinary and reproductive tracts that open in the exterior through the cloaca. 
• Their heart has three chambers and is cold-blooded. 
• The respiration process is by lungs, skin, and gills. 
• The reproduction by different sexes and internal fertilization takes place. 
• They are oviparous animals with indirect development. 
• Some examples are toads and frogs

Class – Reptilia

• They are creepers and crawlers under this phylum.
• They are mainly terrestrial with dry and confined skin cover.
• These have epidemic scales or scutes on their skin. 
• Snakes and lizards at the time skin shed to remove the scales. 
• There is no ear opening and the Tympanum acts as an ear. 
• They have three chambers in their hearts and crocodiles have four.
• Reptiles are cold-blooded animals.
• They can lay eggs outside water as it has a hard covering. 
• The male and female sexes are different from internal fertilization. 
• They are oviparous animals with direct development. 
• Some examples are Turtle, Crocodile, Alligator, Wall lizard, Vipera, etc.

Class – Aves

• They have four chambers in their hearts and use lungs for breathing.
• All the birds are Aves.
• They have feathers and can fly except flightless birds like Ostrich.
• Their wings act as their forelimbs.
• The scaled hind limbs enable them to walk, swim, and climb trees. 
• They only have oil glands at the tail, making the rest of the skin dry.
• Their bones are hollow with air cavities. 
• The crop and gizzard are digestive tracts of them.
• They come under warm-blooded animals. 
• They use lungs to respirate and air sacs near them.
• These have different sexes with internal fertilization.
• They are oviparous animals with direct development.
• Some examples are Crow, Pigeon, Vulture, etc.

Class – Mammalia

• They have four chambers in their hearts and use lungs for breathing.
• They are warm-blooded animals.
• Most of them reproduce young except platypus who lay eggs. 
• They are mostly terrestrial animals except a few who can fly and live underwater.
• They have milk-producing glands for infants’ nourishment. 
• These have two limbs for walking and other activities. 
• Their skin has hair, external ears, and types of teeth in their jaws.
• They have different sex with internal fertilization and direct development. 
• They are mostly viviparous animals except for kangaroo, dolphins, and blue whales.
• Some examples are Platypus, Viviparous – Kangaroo, Flying fox, Delphinus, etc.

Salient Features of Different Subclasses in the Phylum Vertebrata 

Subclasses	Heart	Reproduction	Fertilization	Development	Respiration	Blood
Cyclostomata	Two Chambers	Oviparous	External	Indirect	Gills	–
Pisces	Two Chambers	Oviparous	Internal/ External	Direct	Gills	Cold Blooded
Amphibia	Three Chambers	Oviparous	Internal	Indirect	Lungs/Gills	Cold Blooded
Reptilia	Three Chambers	Oviparous	Internal	Direct	Scales	Cold Blooded
Aves	Four Chambers	Oviparous	Internal	Direct	Lungs	Warm-Blooded
Mammalia	Four Chambers	Viviparous	Internal	Direct	Lungs	Warm-Blooded

Important Animal Kingdom Point to Remember

• The organism under this kingdom is multicellular eukaryotes without any cell walls. They are heterotrophs and depend on plants for food. 
• They have a fixed growth cycle with a definite shape or size for each phase or cycle. These can locomote or follow a clear movement and follow sexual reproduction.
• The Porifera have cellular levels of an organization and are multicellular. They are attached to a solid support as they are non-motile. There is minimal differentiation in body design with tissue division. 
• The Platyhelminthes have a bilaterally symmetric body. They are triploblastic and have a tissue level organization. They are flatworms as they have a flat body top to bottom. 
• The Ctenophora are aquatic and diploblastic. They also have a radical symmetry body structure. They have a tissue-level organization of cells.
• The Aschelminthes have a cylindrical shape and are not flat. They have an organ system level cell arrangement. They are triploblastic with a body cavity presence.
• The Annelida are marine or terrestrial. They can be free-living or parasitic. It has a segmented body surface. They have an organ system level cell arrangement.
• The Mollusca have an organ system level cell organization. They have a bilaterally symmetric structure and are triploblastic. The circulatory system is open and a kidney-like organ for waste excretion. 
• Echinoderms have an endoskeleton of calcium carbonate. They are marine animals and free living. They have an organ level cell arrangement and are triploblastic with a cavity for true organs. 
• Hemichordata has worms like marine organisms with an organ level cell arrangement. They are bilaterally symmetric with triploblastic organization and cavity for true organs. 
• The main feature of Chordata is the presence of a notochord, hollow nerve cord, and paired pharyngeal gill. They are bilaterally symmetric with an internal cavity for true organs. 
• The vertebrates are an important subphylum under Chordata. They further have subclasses – Cyclostomata, Pisces, Amphibia, Reptilia, Aves, and Mammalia.
• The mammals have milk-producing glands for infants’ nourishment. 
• The Aves have feathers and can fly except flightless birds like Ostrich.
• The reptilia are creepers and crawlers under this phylum.
• The amphibians class can easily survive in aquatic and terrestrial environments. 
• Pisces are the fishes under this class with scales and plates.
• Cyclostomata is the ectoparasite that survives on fishes underwater. 

Conclusion

All the subclasses of the phylum Vertebrata have a few similarities. This is because they come under the same kingdom and somehow connected to the same origin. Thus they evolved over time to create different classes.

The main difference comes from their diversity which is greater in the Mammalia subclass. This article will guide you on their features, structure, classification, and characteristics with examples. 

There are details for each subhead mentioned before with light on all features. The UPSC Prelims may have a question from this topic as it comes under basic science.

Other competitive exams like RRB, SSC, Banking, and more will also have an interest in this to check the candidate’s general knowledge. All the UPSC Aspirants must go through this article once to understand basic science topics.