Phylum Chordata: What are chordates? The Phylum Chordata is one of the phyla that belong to the kingdom Animalia. These Chordates possess a flexible rod-like structure formed of a material similar to cartilage known as the notochord. Do you have a backbone? Are we egg-laying animals? Do we have wings to fly? All these doubts will be cleared through this article. This article covers topics like the characteristic features of the Phylum Chordata, their classification, examples and much more. Read on to find out more interesting facts about the Phylum Chordata.

What Defines the Phylum Chordata?

Phylum Chordata is one of the phyla that belongs to the Kingdom Animalia which includes all the vertebrates and invertebrates. They possess a bilaterally symmetrical body and are divided into three different sub-phyla called Urochordata, Cephalochordate and Vertebrata.

Characteristics of Phylum Chordata

Animals belonging to phylum–Chordata is characterised by the presence of the notochord, dorsal tubular nerve cord, gill-clefts and a post-anal tail. These four structures are found in the embryological stages of all chordates. Phylum Chordata possesses the following characteristic features:

1. Notochord – It serves as a primitive internal skeleton. It may persist throughout life, as in Cephalochordata, Cyclostomata and some fishes. It may be replaced partially or completely by a backbone or vertebral column.
2. Dorsal Tubular Nerve Cord – It lies above the notochord and persists throughout life in most chordates, but in a few, it degenerates before maturity.
3. Gill Clefts – They appear during the development of every chordate, but in many aquatic forms, they are lined with vascular lamellae, which form gills for respiration.
4. Post-anal tail – It is an extension of the body that runs past the anal opening. In terrestrial chordates which never breathe by gills, traces of gill clefts are present during early development but disappear before adult life.
5. They are true coelomates.
6. These chordates have a paired lateral appendage in the form of limbs or fins.
7. All vertebrates are chordates, but all chordates are not vertebrates because, in vertebrates, the notochord is present in an embryonic stage which is replaced by a vertebral column in adults.

Fig: General Chordata Characters

Phylum Chordata Classification Chart

The Phylum Chordata Classification is shown through a flow chart given below:

Classes of Phylum Chordata

The Classification of the Phylum Chordata are as follows:

Subphylum Urochordata

Urochordata (Greek: Uro – tail; chorde – cord) is one of the subphyla of the Phylum Chordata and exhibits the following characteristics:
i. They possess two openings on their body surface – mouth and atriopore.
ii. The notochord is present only in the larval tail.
iii. The larva undergoes retrogressive metamorphosis to form an adult.

? Do you know this?

Metamorphosis is the process by which a larva undergoes structural, functional, biochemical and physiological changes to be gradually transformed into an adult. If a simple larva is transformed into a complex adult, then the process is called progressive metamorphosis (caterpillar to butterfly). If a complex larva is transformed into a simple adult, then the process is known as retrogressive metamorphosis (tadpole larva to Ascidia)

Subphylum Cephalochordata

Cephalochordata (Greek: Cephalos – head; chorde – cord) is one of the subphyla of the Phylum Chordata and exhibits the following characteristics:
i. The notochord extends from head to tail region, and it is persistent throughout their life.
ii. Animals do not have heads. The body has a trunk and tail. Exoskeleton absent.
iii. Animals are marine and found in shallow water.

Subphylum Vertebrata

This is one of the subphyla of the Phylum Chordata and exhibits the following characteristics:
i. They possess an endoskeleton made up of bone and cartilages.
ii. Presence of cranium or brain box that accommodates the brain.
iii. Presence of dorsal-ventral column formed of vertebrae.
iv. Subphylum Vertebrata is again divided into two sections, namely, Section Agnatha and Section Gnathostomata.

Section Agnatha

i. Agnatha (Greek: Gnathos – mouth; a – without) members have a mouth that is circular and absence of jaws surrounding the mouth.
ii. No paired fins and fins are without fin rays.

Class Cyclostomata

Class Cyclostomata (Greek: Cyclos – circular; stome – mouth) is a class of Division Agnatha and exhibits the following characteristics:
i. They are ectoparasites on some fishes.
ii. They have an elongated body with \(6\) to \(15\) pairs of gill slits for respiration.
iii. They have a sucking and circular mouth without jaws.
iv. The circulatory system is of closed type.

Section Gnathostomata

i. Gnathostomata (Greek: Gnathos – jaw; stome – mouth) members are animals with jaws, i.e., the mouth is guarded by the upper and lower jaw.
ii. Their skeleton is made up of bones.
iii. Respiration is by lungs or gills.
iv. The division Gnathostomata is divided into superclass Pisces and superclass Tetrapoda.

Superclass Pisces

It includes fishes and is classified into subclasses, namely, Chondrichthyes and Osteichthyes.

Chondrichthyes	Osteichthyes
1. They are known as cartilage fishes with a cartilaginous endoskeleton.	1. They are known as bony fishes with a bony endoskeleton.
2. They are marine habitats.	2. They are both fresh and marine water habitat.
3. Mouth ventrally placed in the head.	3. Mouth at the tip of the head.
4. The air bladder is absent.	4. The air bladder is present.
5. Gills are not covered by the operculum.	5. Gills are covered by an operculum
6. They are unisexual and fertilization is internal.	6. Sexes are separate and fertilization is external.

Superclass Tetrapoda

It includes Vertebrata characterized by two pairs of limbs. It includes four classes, namely, Amphibia, Reptilia, Aves and Mammalia.

Class Amphibia

The name indicates that amphibians can live in both aquatic as well as land habitats.
i. They exhibit the following features: Their skin is moist and smooth due to mucus glands.
ii. They are poikilothermic animals, i.e., cold-blooded animals.
iii. They have two pairs of limbs, a pair of forelimbs with four digits and hindlimbs with five digits.
iv. Respiration is through gills in tadpoles and by lungs and skin in adults.
v. The tympanum represents the ear, and eyes are provided with movable eyelids and a nictitating membrane.
vi. The heart is three-chambered with two auricles and one ventricle.
vii. Sexes are separate, animals are oviparous, and fertilization is external. Development is indirect with a tadpole larva.

Class Reptilia

These are the first true terrestrial vertebrates and exhibit the following characters:
i. Their skin is dry, the tough glands and it is covered by epidermal scales.
ii. They are poikilothermic animals, and the body is divisible into head, neck, trunk and tail.
iii. Two pairs of pentadactyl limbs with a claw that help in crawling locomotion.
iv. The heart is three-chambered with two auricles and one ventricle. The crocodile is an exception as it has a four-chambered heart.
v. Respiration is by lungs.
vi. Sexes are separate, fertilization is internal. Development is direct, and they are oviparous.

Class Aves

The members of this class are commonly known as birds and exhibit the following characters:
i. They have a streamlined, or boat-like or spindle body that offers resistance while flying.
ii. They are homeothermic animals, i.e., warm-blooded animals with aerial habitat.
iii. The forelimbs are modified into wings that function as an organ of flight.
iv. The body in birds is covered by feathers made up of keratin protein.
v. Hind limbs are shifted forward to balance the body while walking.
vi. The jaws are modified into a toothless beak.
vii. Respiratory organs are lungs, which are spongy, compact and contain thin-walled extensions called air sacs.
viiI. The heart is four-chambered with two auricles and two ventricles.
ix. Bones are air-filled or pneumatic; hence they are light and adopted for easy flight.
x. In the excretory system, the urinary bladder is absent to reduce body weight.
xi. Nitrogenous waste is eliminated in the form of uric acid.
xii. Members are oviparous, fertilization is internal.
xiii. Members can be divided into two groups, namely, flying birds like parrots, pigeons, etc., and flightless birds like ostrich, kiwi, etc.

Class Mammalia

The members are commonly called mammals as they narrate their young ones with the help of mammary glands. They exhibit the following characters:
i. The body has an exoskeleton made up of epidermal hair.
ii. They are homeothermic animals, and some are secondarily adapted for living in water – Whales.
iii. The eyes have movable eyelids with eyelashes.
iv. The ears have a fleshy ear pinna.
v. Limbs are typically pentadactyl, adapted for walking, running, climbing, swimming, etc.
vi. The alimentary canal opens to the exterior by the anus.
vii. A muscular diaphragm is present, which divides the body onto the upper thorax and lower abdominal cavity.
viii. Different types of teeth are present (heterodont condition) embedded in sockets of the jawbones (thecodont). Two sets of teeth occur during a lifetime, a milky set and a permanent set (diphyodont condition).
ix. The brain is well developed, and respiration is by the lungs.
x. The heart is four-chambered, maintains complete double circulation and RBCs are enucleated.
xi. They are viviparous, sexes are separate, and fertilization is internal and development is direct.
xii. There are some mammals that are oviparous, like Platypus and Echidna (spiny ant-eater).

? Did you know?

?The hippocampus is a seahorse and is called a sea horse, because it looks like a small horse.
? The scientific name of Rohu fish is Labeo rohita.
? Mangur is also known as cat fish. Its scientific name is Clarias batrachus).
? Shark or scoliodon is known as dog fish and torpedo is known as electric ray.

Phylum Chordata Examples

The examples of the phylum Chordata are given below:

Phylum Chordata: Examples are lamprey, lancelets, dog, human etc.

Fig: Lamprey

Subphylum Urochordata: Examples are Ascidia and Salpa.

Fig: Ascidia

Subphylum Cephalochordata: Examples are Amphioxus and Asymmetron.

Fig: Amphioxus

Subphylum Vertebrata: Examples are Shark, frog, lizard, etc.

Fig: Shark

Division Agnatha: Examples are Petromyzon (Lamprey) and Myxine (Hagfish).

Fig: Hagfish

Division Gnathostomata: Examples are fish, birds, etc.

Fig: Fish

Class Chondrichthyes: Examples are Dogfish, Stingray, etc.

Fig: Stingray

Class Osteichthyes: Examples Labeo rohita and Catla catla.

Fig: Labeo rohita

Class Amphibia: Examples are a frog, Salamandra, etc.

Fig: Frog

Class Reptilia: Examples are garden lizard, snake, crocodile, etc.

Fig: Snake

Class Aves: Examples are crow, peacock, parrot, etc.

Fig: Peacock

Class Mammalia: Examples are cats, dogs, human beings, etc.

Fig: Cat

Some Major Marine Animals and Their Associations

Sea Anemones	Cnidaria
Sea Hare	Molska
Sea Cucumber	Echinoderm
Sea Fan	Cnidaria
Sea Cow	Mammals
Sea Horse	Pieces
Sea Lily (Sea LIly)	Echinoderm
Sea Urchin	Echinoderm
Sea Mouse	Annelida
Sea Pen	Cnidaria

Important Facts Related to Phylum Chordata

Here are some of the important facts related to phylum chordata:

Which era is called the era of reptiles?

• Mesozoic era

Which is the only poisonous lizard in the world?

• Hiloderma

Which is the only snake that builds a nest?

• King Cobra

Which is the most poisonous terrestrial snake?

• King Cobra

Birds that cannot fly

• Kiwi, Emu

Which is the largest living bird?

• Ostrich

Whose blood temperature is the highest in the mammal category?

• Goat

Which is the only venomous mammal?

• Duck Wild Platypus

Summary

Phylum Chordata is a vast phylum as it includes many subphyla, superclass and classes. All vertebrates are chordates, but all chordates are not vertebrates. The notochord is an elongated rod-like flexible structure extending the length of the body. These possess a backbone and possess many special features like a nictitating membrane, movable eyelids, where birds have wings that are modified forelimbs. All mammals, birds, reptiles, amphibians come under the phylum Chordata.

FAQs

Q.1. What is the major difference between chordates and non-chordates with respect to the nerve cord?
Ans: All chordates have dorsal hollow nerve cords. Conversely, non-chordates have ventral, solid nerve cords.

Q.2. Which class do humans belong to?
Ans: Humans belong to the class Mammalia.

Q.3. What is Notochord?
Ans: This is the first skeleton laid during the embryonic development of the chordates. The notochord is an elongated rod-like flexible structure extending the length of the body. The phylum Chordata have the characteristic notochord, dorsal nerve cord and pharyngeal slits.

Q.4. What are the \(5\) characteristics of chordates?
Ans: The \(5\) characteristics of chordates are as follows:
I. They possess a notochord.
II. They have a dorsal tubular nerve cord.
III. Pharyngeal gill slits present in the embryonic stage may be functioning throughout the life or replaced by lungs.
IV. They are true coelomates.
V. These chordates have a paired lateral appendage in the form of limbs or fins.

Q.5. Explain phylum Chordata with an example?
Ans: The members of the phylum Chordata have notochord; a dorsal hollow tubular nerve cord filled with cerebrospinal fluid and also present pharyngeal gill slits. Example – Lamprey.

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