In the animal kingdom, the classification of several species is made by taking into account the various physical, structural, functional, behavioral, and biological parameters. One of the biggest classifications known in the animal kingdom is the vertebrates and the invertebrates. This corresponds to the presence of a backbone or a spinal cord. Although this difference is the most fundamental as it structures the definition of the vertebrates and invertebrates, several differences can be taken into account when understanding more about the species that are segregated based on the above-mentioned classification.
Vertebrates also called Chordates are the most advanced species in the animal kingdom. These animals possess a well-defined internal skeleton system including the backbone which is termed as a spinal column or spinal cord. In human beings, the spinal cord runs in the body between the caudal and cranial regions and hence it plays a vital role as it establishes connections between the nerve tissues. Vertebrates have more complex and specialized organ systems when they are compared with invertebrates. Organs or the organ systems like the respiratory systems are very much complex due to many additional functions. Even the sensory organs present in vertebrates are advanced. And these are helping the vertebrates to adapt to their respective environment. Examples of vertebrates are mammals, birds, fishes, etc.
On the contrary to vertebrates, it can be defined that the invertebrates also known as non-chordates are animals that do not have a backbone or spinal column. They can be found almost everywhere, from the hottest deserts and darkest caves to the tallest mountains and the deepest seabed. Invertebrates are animals without a skeletal system. Most invertebrates lack a robust body structure. They cannot grow very large for this reason. In terms of anatomy, invertebrates have an open circulatory system and blood flows inside their open cavities. Invertebrates also possess a simple respiratory system. To compensate for the lack of an internal skeletal structure, invertebrates have an external skeleton to protect their soft, inner body. Such materials are usually made from chitin, a derivative of glucose. Invertebrates are constituting more than 95 percent of all species on the earth. Some main examples are arthropods, annelids, bivalves, squids, octopuses, coelenterates, echinoderms, sponges, and snails .
Despite the obvious differences mentioned by definition between the vertebrates and the invertebrates, several other parameters contributing to the difference between the two classifications of species, some of them are shown below as follows:
|Structural||The organisms that have a skeletal structure or a spinal column||The organisms that do not have a skeletal structure or a spinal column|
|Exoskeleton||The vertebrates do not require exoskeleton; however, some vertebrates do possess exoskeleton as well||Some organisms have exoskeletons in order to maintain their structural integrity|
|Size||Comparatively larger body size as it has structural support||Inherently smaller than vertebrates as there is no structural support|
|Body||All the vertebrates have bilateral body symmetry||Invertebrates have either radial or bilateral body symmetry|
|Nervous System Distribution||The nervous system is well organized for its complexity and distributed through the spinal column||The nervous system is a very simple distribution with an unorganized nervous system|
|Nervous System Structure||In case of vertebrates, the nervous system structure is hollow||In case of invertebrates, the nervous system structure is solid|
|Circulatory System Distribution||The circulatory system in vertebrates is closed with the utilization of arteries and veins||The circulatory system in invertebrates is open as there is no organization in the distribution|
|Classification Distribution||5% of the total animal species are vertebrates||95% of the total animal species are invertebrates|
|Nutrition Acquirement||The mode of vertebrates in acquiring nutrition is heterotrophi||The modes of invertebrates in acquiring nutrition are heterotrophic, parasitic, and autotrophic|
|Reproduction modes||The sexual reproduction is predominant||The asexual reproduction is predominant|
|Body temperature||They can be both cold and warm-blooded||They are all cold-blooded|
|Regeneration||Vertebrates have a low power of regeneration||Invertebrates have a greater power of regeneration|
|Limb Distribution||They are all derived from different segments||They are all derived from the same segment|
|Examples||Mammals, birds, fishes, reptiles, amphibians, and so on||Worms, sponges, arthropods, insects, and so on|
In conclusion, the classification of vertebrates and invertebrates is essential as it maps out the overall functional, behavioral, and biological units of all organisms. It is also worth pointing out that although vertebrates count as more evolved, developed, and complex organisms, they constitute up to 5% of the total animal species. That implies that the lesser developed species or invertebrates are still at their state of further evolution for the next hundreds of thousands of years to come.