In the vast realm of the animal kingdom, two distinct groups emerge: chordates and non chordates. These two animal groups are differentiated primarily by the presence or absence of a notochord, a flexible rod-like structure that runs along the length of the body. Chordates include vertebrates such as fish, amphibians, reptiles, birds, and mammals. Non chordates include invertebrate groups such as arthropods (insects, crustaceans), mollusks (snails, squids), and annelids (earthworms, leeches). Understanding the contrasting characteristics of chordates and non chordates is important for unraveling the complexities of animal diversity.
Last updated date: 25th Sep 2023
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Anatomy of Chordates
Notochord: Chordates possess a notochord, a stiff, yet flexible structure located along the dorsal side of the body. It provides support and allows for efficient movement.
Dorsal Nerve Cord: Chordates have a dorsal nerve cord, a hollow neural tube located above the notochord. This cord gives rise to the central nervous system, including the brain and spinal cord.
Pharyngeal Slits or Clefts: Chordates possess pharyngeal slits or clefts, which are openings in the pharynx. In some chordates, these structures are involved in respiration, while in others, they play a role in filter-feeding or are modified for other functions.
Post-anal Tail: Chordates have a post-anal tail that extends beyond the anus. This tail helps in locomotion and provides balance in aquatic species. In some terrestrial species, it is reduced or lost during development.
Anatomy of Non Chordates
Absence of Notochord: Non chordates do not have a notochord. Instead, they have other support structures like an exoskeleton (arthropods), or a hydrostatic skeleton (worms).
Ventral Nerve Cord: Non chordates have a ventral nerve cord, located along the ventral side of the body. This cord gives rise to the nervous system and runs along the length of the body.
Different Body Plans: Non chordates exhibit various body plans, including bilateral symmetry (insects, worms), radial symmetry (jellyfish, sea anemones), and asymmetry (sponges).
Various Appendages: Non chordates possess various appendages specialized for different functions, such as locomotion, feeding, or sensory perception. Examples include legs, antennae, tentacles, and wings depending on the specific group of non chordates.
Reproduction in Chordates
Chordates exhibit various reproductive strategies, but the most common method of reproduction is sexual reproduction. Different sexual reproduction methods in chordates are:
External Fertilization: Some chordates, especially fish and amphibians, follow external fertilization. Here, eggs released by the female are fertilized by the sperm released by the male outside the body. Both eggs and sperm are released at the same time.
Internal Fertilization: Many chordates, including reptiles, birds, and mammals, follow internal fertilization. Here, the sperm is deposited directly into the female’s reproductive tract, allowing for internal fertilization of the eggs. This method offers protection to the developing embryos and increases the chances of successful reproduction.
Oviparity: Oviparous chordates lay eggs that develop and hatch outside the mother’s body. Examples include reptiles, birds, and monotremes. The eggs contain all the nutrients required for embryonic development until they hatch.
Viviparity: Viviparous chordates give birth to live young ones. In this case, the embryos develop inside the mother’s body, receiving nourishment through a placenta or other specialised structures. Most mammals, including humans, exhibit viviparity.
Reproduction In Non Chordates
Non chordates employ a range of reproductive strategies depending on their specific characteristics and adaptations. Different ways by which non chordates reproduce are mentioned below.
Asexual Reproduction: Many non chordates reproduce asexually, where they produce offspring without the involvement of gametes or the fusion of genetic material. This type of reproduction enables rapid multiplication and colonization in some species. Different asexual reproduction methods in non chordates are:
Binary fission: In binary fission, a single parent cell replicates its DNA, enlarges in size, and then divides into two daughter cells.
Budding: Budding involves the development of a bud (a new individual) from an existing parent organism. The bud grows on the parent organism and eventually detaches to become an independent organism.
Fragmentation: Fragmentation involves the breaking of an organism into two or more fragments, each of which can develop into a new individual.
Parthenogenesis: In parthenogenesis, an organism develops from an unfertilized egg, without the involvement of sperm. It is observed in certain reptiles and fish.
Sexual Reproduction: Sexual reproduction is also prevalent among non chordates and involves the fusion of gametes. Different sexual reproduction methods in non chordates are:
External Fertilization: Some non chordates follow external fertilization, where eggs and sperm are released into the environment simultaneously. Marine invertebrates, including many species of fish, crustaceans, and mollusks, commonly reproduce through external fertilization.
Internal Fertilization: Certain non chordates, including some insects, arachnids, and certain mollusks have evolved through internal fertilization. The male transfers the sperm inside the female’s reproductive tract and fertilization occurs internally.
Hermaphroditism: Many non chordates are hermaphrodites, possessing both male and female reproductive organs. They can produce both eggs and sperm. Some hermaphroditic species can self-fertilize, while others engage in reciprocal mating, exchanging gametes with other individuals.
Complex Reproductive Strategies: Some non chordates, such as bees and ants, exhibit complex social structures and specialized reproductive strategies. These species have reproductive castes, with a queen responsible for egg-laying and specialized individuals (drones) responsible for fertilizing the queen.
Difference Between Chordates and Non Chordates
Notochord is present.
Notochord is absent.
The heart is in a ventral position with hemoglobin, red blood cells, and limbs.
The heart may be in a dorsal or lateral position with the limbs.
They have a closed circulatory system.
They usually have an open circulatory system.
Respiration is via the gills or lungs.
Respiration is via gills, trachea, or body surfaces.
Hemoglobin is present.
Hemoglobin is absent. Instead, hemolymph is present.
They are bilaterally symmetric.
They can be radial, bi-radial, asymmetrical, or bilateral.
Some examples include fishes, birds, reptiles, amphibians, and mammals.
Some examples include insects, sponges, annelids, protozoans, and arthropods.
This article aims to explain chordates and non chordates. Chordates and non chordates represent two distinct groups within the animal kingdom. Chordates, with their notochord, backbone, complex nervous system, closed circulatory system, diverse reproductive strategies, and specialized sensory organs, have evolved to be highly adaptable and exhibit a wide range of anatomical and physiological variations. Non chordates, lacking a notochord and true backbone, display diverse characteristics and mechanisms that have allowed them to thrive in various ecological niches. Understanding chordates and non chordates difference provides valuable insights into the vast diversity of life on Earth.
FAQs on Difference Between Chordates and Non Chordates
1. What is a notochord?
A notochord is a flexible rod-like structure found in the embryos of chordate animals. It has several important functions: providing structural support, induction of neural tissues, and development of vertebrates. During later stages of embryonic development, the notochord largely regresses and is replaced by the vertebral column or backbone in vertebrates.
2. What are the characteristics of chordates and non chordates?
Chordates possess a notochord, while non chordates possess an exoskeleton or hydrostatic skeleton instead of a notochord. Chordates have a dorsal nerve cord, while non chordates have a ventral nerve cord. Chordates have pharyngeal slits or clefts, thyroid glands, and post-anal tails, while non chordates do not have them.
3. Why is it important to know the chordates and non chordates difference?
Understanding the difference between chordates and non chordates is important for several reasons: to know the taxonomy and classification, to understand the evolutionary significance, to compare anatomy and physiology, to understand ecological roles and interactions, and to contribute to medical and scientific research.