The classification of animals largely can be done into two groups: invertebrates and vertebrates. The basic difference between the two is the presence of backbone or a spinal column. Animals like birds, snakes, and human beings are vertebrates due to the presence of backbone and flatworms and insects are the examples of invertebrates. It is worthy to be mentioned here that 98 percent of the animals on the earth are invertebrates and only 2 per cent create the vertebrates. The vertebrates can be classified into five groups like mammals, birds, reptiles, amphibians and fish; whereas the vertebrates are classified as 30 phyla.
The animals that do not possess or develop the vertebral column that is usually grown from the notochord are termed as the invertebrates. Except the subphylum Vertebrata, this class includes all the animals. This class of animals do not possess a backbone and they can exist anywhere on the surface of the earth. In the canopies of wettest rainforests, high reaches of the atmosphere and driest of deserts; these groups of animals can be found. Even under the deepest oceans and frozen Antarctic – these animals can exist. Below mentioned are some of the terrestrial invertebrates; however many others are also found in fresh water as well as marine environments.
- Velvet worms
Invertebrates living in freshwater as well as in the marine environment include the following groups. However, some of these are also found to live on the land as well.
- Lobsters crayfish prawns & crabs.
- Jellies and bluebottles.
- Slugs and snails.
- Corals and anemones.
- Sea urchins and sea stars.
While discussing the meaning of invertebrates, it is evident here to mention some of the important characteristics of the creature in order to have a better understanding of the same:
- The reproduction of these animals takes place through the fission of gametes.
- As they are not able to produce their own food, this group of animals is heterotrophic in nature.
- They respire with the use of their skin; hence the invertebrates do not have lungs.
- It is generally found that these animals do not grow very large and remain small.
- All invertebrates possess an exoskeleton which skirts around their entire body. They do not possess a vertebral column or a spinal cord.
The Invertebrates can Mainly be Classified into the Kinds as Listed by Phylum:
- Phylum Coelenterata
- Phylum Arthropods
- Phylum Annelida
- Phylum Mollusca
Unlike the invertebrates, vertebrates possess the quality of having a spinal cord. The derivation of the term vertebrate takes from the bones that create the spine. The body of a vertebrate is generally found to be divided into several parts; a brief description of the same is given below:
- Gill arches: Gill arches in some amphibians as well as in the fish basically has the purpose of supporting the gills. Some of the arches in most of the vertebrates are found to be evolved in the form of other organs, jaws as for instance.
- Bones: These are helpful in providing points for the attachment of the muscles and protect and support the soft tissues of the body.
- Vertebrae: Separated with the help of the joints, these basically a series of stiff and short vertebrae. It is basically the backbone that is protective towards the spinal cord. The joints existing between the vertebrae allow the backbone to bend.
- Brain case: A brain case, also called cranium is responsible to protect the brain.
Almost 45, 000species around the earth constitute this group of animals. The verbal column is probably the most important feature that makes the difference but it is to be noted here it did not exist in terms of the first vertebrates. It is considered that they probably had only one notochord. The vertebrates are generally found to have three sense organs’ pairs including otic, optic and nasal; a differentiated tubular brain along with a separate head. Generally their body is divided into tail and trunk regions and the presence of gills with pharyngeal slits signify that their metabolic rate is relatively high. Depending on the morphological facts and phenomena, the vertebrates are generally subdivided into the following groups:
- the tetrapods,
- the teleostomes (bony fishes),
- the chondrichthyes (cartilaginous fishes); and
- the cyclostomes (jawless fishes).
The size of the vertebrates is widely varied and involves small fish as well as large whales and elephants. A vertebrate may weigh up to 100 tons. The largest animal that has ever existed on the surface of the planet is a vertebrate. They can be found in the air, on the surface as well as under the ground. The vertebrates are generally found to be dependent on the invertebrates, the plants as well as one another. To human beings, for the purpose of recreation and food, vertebrate faunas are significantly essential. They belong from the kingdom Animalia and possess bilateral symmetry that can be separated into two groups: deuterostomes and protostomes depending on their embryonic development pattern. In all the vertebrates, a stiff runs through the entire body of the animal along with a nervous tissue which actually is a hollow tube – like structure. At the anterior end of the body, there exists a mouth and before the posterior end there exists an anal.
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- Invertebrates do not possess a backbone and they can exist anywhere on the surface of the earth.
- Animals like birds, snakes, and human beings are vertebrates.
- The derivation of the term vertebrate takes from the bones that create the spine.
- The vertebrates are generally found to be dependent on the invertebrates, the plants as well as one another.