What are invertebrates?
The animals which lack the backbone or the vertebral column are referred to as Invertebrates. All such animals are included in a group called Invertebrata.
Also, animals are often categorized into two major groups : the chordates and the non-chordates. This categorisation or division is based on the presence or absence of the singular character the notochord. It is a stiff rod-like structure which serves as an internal skeleton.
Animals without notochord are called non-chordates and those with vertebral column are called chordates. Non-chordate and invertebrate are the terms often used for each other as synonyms but their meanings differ. For an instance, protochordates are all invertebrates because of the absence of vertebral column but they still are chordates due to presence of notochord. Thus, all the non-chordates are invertebrates whereas all invertebrates are not non-chordate.
Presently, there are about 30 invertebrate phyla which are characterized by the unity of basic structural pattern in each of them. For example, Phylum Arthropoda which includes insects, arachnids, crustaceans, etc. has an estimated 9,99,059 identified species or 85% of total identified animal species. Apart from arthropods, the invertebrates number reaches 12,38,000 or 94% excluding viruses and bacteria.
Significance of invertebrates:
Well-known biologist E. O. Wilson has described the invertebrates as, "little things which run the world". Invertebrates are a portion of nearly every food chain directly as food for fishes, amphibians, reptiles, birds, mammals or indirectly as agents in the continual recycling of nutrients in the soil. Food webs depend on these creatures executing essential procedures such as pollination or seed dispersal. We can't think of living on the earth without the existence of invertebrates.
Importance of study of invertebrates:
The study of invertebrates has acquainted us with their involvement in the significant effects on the sustainability of numerous agrarian products. Invertebrates and microorganisms play an important role in detoxifying pesticides, nurturing and enhancing the fertility, reducing the effects of pollutants and also in biological control of agricultural pests. Many invertebrates are deadly to humans as parasites (nematodes) or as vectors for serious human diseases (mites, mosquitoes).
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