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Chordata

Phylum Chordata is one of the most well-known and diverse phyla in the Animal Kingdom. It includes animals ranging from simple marine organisms to highly complex vertebrates like humans.

1.0Introduction

Organ system level of organisation
Bilaterally symmetrical, triploblastic, and coelomate animals
Notochord
Dorsal hollow nerve cord
Paired pharyngeal gill slits
Closed circulatory system
Post anal tail

2.0Characters of Chordates

All the chordates possess four diagnostic characters either in the embryonic or adult stage.
Notochord: It is a solid un-jointed, stiff but flexible rod-like structure situated on the dorsal side between the dorsal hollow nerve cord and the alimentary canal.
Dorsal Hollow Nerve Cord: The nerve cord of chordates is always hollow and lies dorsal to the notochord.
Pharyngeal Gill Slits: All the chordates have at some stage of life, a series of paired narrow openings, the gill slits on the lateral sides of the pharynx.
Tail: It is a post-anal part of the body.Which is reduced or absent in many adult chordates.

Other Characters of Chordates

These include bilateral symmetry, three germinal layers, segmentation, organ-system level of organisation, cephalization, coelom, endoskeleton, complete digestive tract, special organs for respiration and excretion, closed circulatory system, separate sexes, gonads with gonoducts and without asexual reproduction.

Phylum Chordata can be divided into two groups:

Acrania (Protochordata)
Craniata (Euchordata) which show contrasting characters.

Acrania (Protochordata)

All are marine, small, primitive or lower chordates.
No cranium, jaws, vertebral column, paired appendages.
About 2,000 species.
The Acrania is divided into three subphyla- Hemichordata, Urochordata and Cephalochordata.

3.0Subphylum I. Hemichordata

The body is divided into 3 regions- proboscis, collar and trunk.
Notochord doubtful, short confined to proboscis and non-homologous with that of chordates.

Class 1. Enteropneusta

Body large and worm-like. Gill-slits numerous and paired.
Alimentary canal straight. Acorn or tongue worms.
Enteropneusts include 3 families, 15 genera and 70 species.
Examples- Balanoglossus, Saccoglossus, Ptychodera.

Class 2. Pterobranchia

The body is small and compact.
Gill-slits one pair or none, never U-shaped.
Alimentary canal U-shaped.
Pterobranchs include 2 orders, 3 genera and 20 species.
Examples- Cephalodiscus, Rhabdopleura.

Class 3. Planctosphaeroidea

Transparent, round and specialised tornaria larva possessing extensively branched ciliary bands.
Alimentary canal L-shaped.
Planctosphaera pelagica is a representative of this class.
This form is supposed to be specialised tomaria larva of some unknown hemichordate.

Class 4. Graptolita

The fossil graptolites (e.g., Dendrograptus) were abundant in Ordovician and Silurian periods.
These are often considered as an extinct colonial class of Hemichordata.
Their tubular chitinous skeleton and colonial habits show an affinity with Rhabdopleura.

4.0Subphylum II. Urochordata or Tunicata

Notochord and nerve cord in tail only in minute free-swimming tadpole larva.
Adult sac-like, covered with tunic (test) often transparent; usually no notochord nerve cord reduced to ganglion; no coelom, segmentation or nephridia.

Class 1. Ascidiacea

Sessile tunicates with scattered muscles in tunic. Solitary, colonial or compound. Gill-slits many; tunic well developed, permanent.
Ascidians or sea squirts. Include 3 orders, 12 families, 37 genera and 1,200 species. Examples- Herdmania, Ciona and Molgula.

Class 2. Thaliacea

Free-swimming or pelagic tunicates with circular muscle bands in tunic.
Salpians and chain tunicates.
Include 3 orders, 5 families, 9 genera and 30 species.
Examples- Salpa, Doliolum, Pyrosoma.

Class 3. Larvacea or Appendicularia

Tiny, transparent, free-floating. Adults retain many larval features including tails. Only two gill-slits.
Tunic not persistent.
Include 2 orders, 2 families, 5 genera and 3 species.
Examples- Oikopleura, Appendicularia.

5.0Subphylum III. Cephalochordata

Notochord and nerve cord present throughout life along the entire length of the body.
Include 1 class, 1 family, 2 genera and 30 species.

Class Leptocardii

Body fish-like, segmented with numerous gill-slits.
Free-swimming and burrowing. Lancets.
Examples- Branchiostoma (= Amphioxus), Asymmetron.

Group B. Craniata

Aquatic or terrestrial, usually large-sized, higher chordates or vertebrates with distinct head, a vertebral column, jaws and brain protected by a cranium or skull.
The craniata includes a single subphylum Vertebrata.

6.0Subphylum IV. Vertebrata

Notochord supplemented or replaced by a vertebral column or backbone consisting of overlapping vertebrae.
Body divisible into head, neck, trunk and tail. Usually dioecious.
Vertebrata is the largest chordate subphylum including about 45,000 species.

Frequently Asked Questions

Join ALLEN!

(Session 2026 - 27)

Name

Mobile Number

Class

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Goal

Choose your goal

Preferred Programs

Preferred Mode

State

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I agree to

I authorise ALLEN Career Institute Pvt Ltd to send me regular updates via Phone calls, Whatsapp, SMS, Robocalls (Automated Calls), Emails, or on postal address.

Chordata

Phylum Chordata is one of the most well-known and diverse phyla in the Animal Kingdom. It includes animals ranging from simple marine organisms to highly complex vertebrates like humans.

1.0Introduction

Organ system level of organisation
Bilaterally symmetrical, triploblastic, and coelomate animals
Notochord
Dorsal hollow nerve cord
Paired pharyngeal gill slits
Closed circulatory system
Post anal tail

2.0Characters of Chordates

All the chordates possess four diagnostic characters either in the embryonic or adult stage.
Notochord: It is a solid un-jointed, stiff but flexible rod-like structure situated on the dorsal side between the dorsal hollow nerve cord and the alimentary canal.
Dorsal Hollow Nerve Cord: The nerve cord of chordates is always hollow and lies dorsal to the notochord.
Pharyngeal Gill Slits: All the chordates have at some stage of life, a series of paired narrow openings, the gill slits on the lateral sides of the pharynx.
Tail: It is a post-anal part of the body.Which is reduced or absent in many adult chordates.

Other Characters of Chordates

These include bilateral symmetry, three germinal layers, segmentation, organ-system level of organisation, cephalization, coelom, endoskeleton, complete digestive tract, special organs for respiration and excretion, closed circulatory system, separate sexes, gonads with gonoducts and without asexual reproduction.

Phylum Chordata can be divided into two groups:

Acrania (Protochordata)
Craniata (Euchordata) which show contrasting characters.

Acrania (Protochordata)

All are marine, small, primitive or lower chordates.
No cranium, jaws, vertebral column, paired appendages.
About 2,000 species.
The Acrania is divided into three subphyla- Hemichordata, Urochordata and Cephalochordata.

3.0Subphylum I. Hemichordata

The body is divided into 3 regions- proboscis, collar and trunk.
Notochord doubtful, short confined to proboscis and non-homologous with that of chordates.

Class 1. Enteropneusta

Body large and worm-like. Gill-slits numerous and paired.
Alimentary canal straight. Acorn or tongue worms.
Enteropneusts include 3 families, 15 genera and 70 species.
Examples- Balanoglossus, Saccoglossus, Ptychodera.

Class 2. Pterobranchia

The body is small and compact.
Gill-slits one pair or none, never U-shaped.
Alimentary canal U-shaped.
Pterobranchs include 2 orders, 3 genera and 20 species.
Examples- Cephalodiscus, Rhabdopleura.

Class 3. Planctosphaeroidea

Transparent, round and specialised tornaria larva possessing extensively branched ciliary bands.
Alimentary canal L-shaped.
Planctosphaera pelagica is a representative of this class.
This form is supposed to be specialised tomaria larva of some unknown hemichordate.

Class 4. Graptolita

The fossil graptolites (e.g., Dendrograptus) were abundant in Ordovician and Silurian periods.
These are often considered as an extinct colonial class of Hemichordata.
Their tubular chitinous skeleton and colonial habits show an affinity with Rhabdopleura.

4.0Subphylum II. Urochordata or Tunicata

Notochord and nerve cord in tail only in minute free-swimming tadpole larva.
Adult sac-like, covered with tunic (test) often transparent; usually no notochord nerve cord reduced to ganglion; no coelom, segmentation or nephridia.

Class 1. Ascidiacea

Sessile tunicates with scattered muscles in tunic. Solitary, colonial or compound. Gill-slits many; tunic well developed, permanent.
Ascidians or sea squirts. Include 3 orders, 12 families, 37 genera and 1,200 species. Examples- Herdmania, Ciona and Molgula.

Class 2. Thaliacea

Free-swimming or pelagic tunicates with circular muscle bands in tunic.
Salpians and chain tunicates.
Include 3 orders, 5 families, 9 genera and 30 species.
Examples- Salpa, Doliolum, Pyrosoma.

Class 3. Larvacea or Appendicularia

Tiny, transparent, free-floating. Adults retain many larval features including tails. Only two gill-slits.
Tunic not persistent.
Include 2 orders, 2 families, 5 genera and 3 species.
Examples- Oikopleura, Appendicularia.

5.0Subphylum III. Cephalochordata

Notochord and nerve cord present throughout life along the entire length of the body.
Include 1 class, 1 family, 2 genera and 30 species.

Class Leptocardii

Body fish-like, segmented with numerous gill-slits.
Free-swimming and burrowing. Lancets.
Examples- Branchiostoma (= Amphioxus), Asymmetron.

Group B. Craniata

Aquatic or terrestrial, usually large-sized, higher chordates or vertebrates with distinct head, a vertebral column, jaws and brain protected by a cranium or skull.
The craniata includes a single subphylum Vertebrata.

6.0Subphylum IV. Vertebrata

Notochord supplemented or replaced by a vertebral column or backbone consisting of overlapping vertebrae.
Body divisible into head, neck, trunk and tail. Usually dioecious.
Vertebrata is the largest chordate subphylum including about 45,000 species.

Frequently Asked Questions

What is Phylum Chordata?

What are the major classes of Chordata?

Are humans part of Phylum Chordata?

What is a notochord?

What is the difference between vertebrates and invertebrate chordates?

Do all chordates have a backbone?

What are pharyngeal slits?

What are examples of chordates?

What are the three subphyla of Chordata?

Why is Phylum Chordata important?

Join ALLEN!

Chordata

1.0Introduction

2.0Characters of Chordates

3.0Subphylum I. Hemichordata

4.0Subphylum II. Urochordata or Tunicata

5.0Subphylum III. Cephalochordata

6.0Subphylum IV. Vertebrata

Table of Contents

Frequently Asked Questions

What is Phylum Chordata?

What are the major classes of Chordata?

Are humans part of Phylum Chordata?

What is a notochord?

What is the difference between vertebrates and invertebrate chordates?

Do all chordates have a backbone?

What are pharyngeal slits?

What are examples of chordates?

What are the three subphyla of Chordata?

Why is Phylum Chordata important?

Join ALLEN!

Chordata

1.0Introduction

2.0Characters of Chordates

3.0Subphylum I. Hemichordata

4.0Subphylum II. Urochordata or Tunicata

5.0Subphylum III. Cephalochordata

6.0Subphylum IV. Vertebrata

Table of Contents