The animal kingdom, sometimes known as Kingdom Animalia, is a well-known categorization of living organisms on Earth. Members of this group are divided into a variety of Genus, Family, Order, Class, and Phyla based on their individual traits. The presence or absence of a notochord on an animal's body is one of the most important factors in animal taxonomy. It's worth noting that a notochord is made of a cartilage-like structure and looks like a flexible rod. Chordates and Non-chordates, both the terms are used for animals and they belong to the different phyla of the Animalia kingdom. The major point to differentiate between chordates and non-chordates is that chordates have a spinal cord or backbone in their body structure whereas non-chordates are without backbone or notochord in their body structure.

The article discusses the different parameters based on which chordates and non-chordates are differentiated. The article also encompasses the description of chordates and non-chordates.

Chordates

A notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail are four important traits that arise at some point during the development of Chordata animals. It is important to note that some of these characteristics are present only in embryonic developmental stages in some of the animals. The characteristic features of Chordates are discussed briefly below.

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Notochord

The notochord is a supportive, stiff rod-like structure which is the characteristic of chordates. It runs the length of the body, in between the alimentary canal and the nerve cord, and provides skeletal stability. In certain chordates, the notochord serves as the body's major axial rigidity. The notochord is prevalent in vertebrates in embryonic developmental stages, where it stimulates neural tube formation and acts as a framework for the growing embryonic structure. The notochord, on the other hand, is absent in the postnatal stage of vertebrates; this has been substituted by the vertebral column or spine.

Dorsal hollow nerve-

The dorsal hollow nerve cord is part of the Central Nervous System of chordates and it is concerned with stimulus and nerve impulses. The dorsal hollow nerve cord is made up of ectoderm that becomes a hollow tube as it develops. It is located dorsally to the notochord in chordates. Most chordate embryos have a nerve cord that grows into the brain and spinal cord, which make up the central nervous system.

Pharyngeal gill-

Pharyngeal gill slits are an important part of the respiratory system and it gets perforated with gill slits. Slits in the pharynx that open externally are known as pharyngeal slits. Pharyngeal slits enable the removal of water that is engulfed into the mouth during feeding. They are seen in creatures that dwell in aquatic habitats. The pharyngeal slits are transformed into gill supports in vertebrates and jaw supports in jawed fishes.

Post anal tail-

Post anal tail is present at the end of the anus in chordates in the form of a short extension. A posterior extension of the body that extends beyond the anus is known as the post-anal tail. In aquatic organisms like fishes, the tail comprises skeletal structures and muscles that facilitate movement. The tail also aids balance, courtship, and alerting when danger is approaching in certain terrestrial animals. The post-anal tail is vestigial in humans, meaning it is small and nonfunctional.

Non-chordates

Let us look briefly into the important features of non-chordates for a better understanding of the differences between the chordates and non-chordates. Non-chordates are creatures that lack the notochord, a rod-like structure in their bodies. Members of the phyla Porifera, Hemichordata, Echinodermata, Mollusca, Arthropoda, Annelida, Aschelminthes, Platyhelminthes, Ctenophora, and Coelenterata are predominantly found in this phylum. This phylum is organised on an organ-system level.

The general features of the non-chordates are mentioned below.

Non-chordates are generally cylindrical, triploblastic, coelomate, or pseudocoelomate.
Non-chordates breathe through the gills, trachea, or the surface of their bodies.
The sexes of the members of non-chordates cannot be differentiated.
Both sexual and asexual reproductive modes exist.
Fertilization is external, while some species have internal fertilisation.
Non-chordates' bodies usually have an open circulatory system.

Difference between chordates and non-chordates

Here is the tabular structure to highlight the differences and students will get an easy understanding to distinguish between chordates and non-chordates in their examinations.

Distinguish Between Chordates and Non-Chordates

Parameters	Chordates	Non-Chordates
Notochord	Presence of cord or notochord.	Absence of cord or notochord.
Limbs	Limbs are two pairs.	Limbs may be more than two pairs.
Heart	The heart is ventral with haemoglobin, RBC and limbs.	The heart is in a dorsal or lateral position with limbs.
Examples	Frog, fish, birds, reptiles, amphibians and mammals.	Cockroach, earthworms, flatworms, jellyfish, sponges, insects, water bears, and other arthropods, annelids and protozoans.
Post anal tail	They have post-anal tails associated with them.	No post anal tail is present in non-chordates.
Circulatory System	Chordates have a closed circulatory system.	Usually, open circulation of blood takes place in non-chordates.
Nerve Cord	Dorsal, hollow and single nerve cord is present in chordates. The nerve cord is without ganglia.	Ventral, solid and double nerve cord is present. The nerve cord of non-chordates has ganglia.
Gill slits	Pharyngeal gill slits are present.	Pharyngeal gill slits are absent.
Respiration	Respiration occurs through the gills or lungs in chordates.	Respiration occurs through the trachea, gills or body surface in non-chordates.
Body fluid	Haemoglobin is present in chordates.	Haemoglobin is absent, instead, hemolymph is present which is analogous to blood in the vertebrates.
Germ layer	Talking about the germ layer, chordates are triploblastic.	Talking about the germ layer of non-chordates, they can be diploblastic, triploblastic or neither.
Symmetry	These animals are bilaterally symmetric.	These animals can be bilateral, bi-radial, asymmetrical or radial.
Coelomates	They are true coelomates.	They can either be true coelomates, acoelomates or pseudocoelomates.
Exoskeleton	The exoskeleton is present in some of the chordates, for example, tortoises.	The exoskeleton is present in all non-chordates.
Endoskeleton	Endoskeleton is present in chordates.	The endoskeleton is absent in non-chordates.
Regeneration	Chordates have poor regeneration.	Non-chordates have good regeneration, mostly.
Anus	The anus of these animals is differentiated and opens before the last segment.	Anus in these animals is usually absent and if present, it opens on the last segment.
Brain	The brain of chordates is present and located dorsal to the pharynx in the head.	The brain is not as complex as that of chordates if present in some of the animals.
Organization	They have a body with an organ system.	Their body organization is protoplasmic to the organ system.

In conclusion, we have learnt about the differences between the two important classifications of the animal kingdom. We have also learnt about the parameters of differentiation.

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FAQs on Difference Between Chordates and Non Chordates

1. Do Chordates Also Include Invertebrates?

Yes, some of the invertebrates fall under the category of chordates as notochord is present in them, however a proper backbone is lacking. Examples of these types of invertebrates include tunicates and lancelets.

2. How is Animal Kingdom Classified? Differentiate Between Chordates and Non Chordates.

Animalia kingdoms are classified as chordates and non-chordates where notochord is present in the former type and it is absent in the latter type.

3. Give Some Examples of the Non-Chordates.

Examples of the non-chordates are present in the phylum including Porifera, Cyonopera, Platyhelminthes, Aschelmenthis, Cyonophera, Annelida, Mollusca, Echinodermata, Hemichordata and Arthropoda. It includes earthworms, flatworms, sponges, jellyfish, cockroaches, etc.

4. What are the Divisions of Chordates?

Chordates can be divided into Urochordates, Cephalochordates and Vertebrates. Vertebrates are classified further into Agnathostomes and Gnathostomes. Gnathostomes can be Pisces (fish) and Tetrapoda on the basis of locomotive structure.

5. What are Some Examples of Different Phyla of Non-Chordates?

Sponges belong to Phylum Porifera, Hydra and Jellyfish belong to Coelenterata; Tapeworm belongs to Platyhelminathes; Earthworm and Leech to Annelida; Snail, Octopus and Pila to Mollusca; Fish, frog, snake, birds, monkey to Chordata; and Scorpion, fly and insects to Arthropoda, and so on.