What are chordates and non-chordates?
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.
(Image will be Uploaded soon)
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
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.
FAQs on Difference Between Chordates and Non Chordates
1. What is the most fundamental difference between a chordate and a non-chordate?
The single most fundamental difference lies in the presence or absence of a notochord. Chordates have a notochord at some stage in their life, which is a flexible rod providing skeletal support. Non-chordates completely lack this structure.
2. What are the three main characteristics that all chordates share?
At some point during their life cycle, all chordates possess three distinct features:
- A notochord (a supportive rod-like structure).
- A dorsal hollow nerve cord (which develops into the central nervous system).
- Pharyngeal slits (openings in the throat area used for feeding or breathing).
3. Can you give some common examples of animals that are non-chordates?
Non-chordates represent the vast majority of animal species. Common examples include animals from various phyla, such as insects (cockroaches), jellyfish (Cnidaria), earthworms (Annelida), snails (Mollusca), and starfish (Echinodermata).
4. Are all chordates also vertebrates?
No, this is a common misconception. While all vertebrates are chordates, not all chordates are vertebrates. The phylum Chordata also includes invertebrate groups called protochordates, such as tunicates and lancelets. These animals possess a notochord but do not have a true backbone or vertebral column.
5. Why is the notochord considered such a key feature in animal classification?
The notochord is crucial because it marks a major evolutionary advancement. It provides primary body support and defines the phylum Chordata. In vertebrates, the notochord is the structure around which the vertebral column (backbone) develops, making it the foundational feature for the entire vertebrate lineage.
6. How does the central nervous system in chordates differ from that in non-chordates?
The difference is a key distinguishing characteristic. In chordates, the central nervous system is dorsal (located on the back), hollow, and single. In non-chordates that have a complex nervous system, it is typically ventral (located on the belly side), solid, and often paired or double.
7. What are the major groups within the phylum Chordata?
Phylum Chordata is broadly divided into three main subphyla:
- Urochordata (e.g., sea squirts or tunicates)
- Cephalochordata (e.g., lancelets)
- Vertebrata (animals with a backbone, like fish, birds, and mammals)
8. Where do humans fit into this classification?
Humans are classified within the phylum Chordata and the subphylum Vertebrata. We exhibit all the key chordate characteristics, such as a notochord and a dorsal hollow nerve cord, during our embryonic development.
9. How does the position of the heart differ between chordates and non-chordates?
The heart's location is another important point of difference. In chordates, the heart is situated on the ventral side of the body (the front or belly side). In non-chordates that possess a heart, it is typically found on the dorsal side (the back side).
