Animals can be classified into two main groups: Vertebrates and invertebrates. The main difference between vertebrates and invertebrates is that invertebrates do not have a backbone or a spinal column. Examples of vertebrates include humans, birds and snakes while examples of invertebrates include insects and flatworms.
|About||Animals without a backbone||Animals with an internal skeleton made of bone are called vertebrates.|
|Physical Characteristics||Multicellular; no back bone; no cell walls; reproduce sexually; heterotrophic.||Well-developed internal skeleton; highly developed brain; have advanced nervous system; outer covering of protective cellular skin.|
|Examples||Insects, flatworms etc.||Parrots, Humans, snakes etc|
|Classification||30 phyla||Classified into five groups: fish, amphibians, reptiles, birds, and mammals.|
|Size||Small and slow moving.||Big in size.|
|Species||98% of animal species are invertebrates.||2% of the animal species are vertebrates.|
|Number of species||2 million||57,739|
Differences in Physical Characteristics
Invertebrates have no back bone while vertebrates have well-developed internal skeleton of cartilage and bone and highly developed brain enclosed by a skull. Their nerve cord is enclosed by the vertebrae and have well-developed sensory organs and respiratory system with either gills or lungs. A bilateral symmetry with advanced nervous system also distinguishes them from invertebrates.
The traits that make all animals in the vertebrates section special are their spinal cords, vertebrae, and notochords. Vertebrates are subdivided into the jawless vertebrates (Agnatha) and the jawed vertebrates (Gnathostomata). While most vertebrates can move and are heterotrophic (cannot make their own food), some invertebrates may be able to make their own food.
Due to lack of a supportive system, majority of the invertebrates are small and only a few reach an impressive size. Invertebrates have two basic body plans: one is the radial symmetry plan (circular body plan arranged around a central mouth, similar to the way spokes radiate out from the hub of a wheel) which includes animals who spend their adult lives fastened in one place. The other is the bilateral symmetry plan (right and left halves that mirror each other, and they typically have a definite front and back end). This includes animals who move in search of food.
Differences in Habitat
Both type of animals live in a variety of habitats but vertebrates can essentially suit themselves in all habitats easily. The highly developed nervous system and internal skeletons of vertebrates make them adaptable to land, sea, and air.
Nevertheless, Invertebrates are also found in a vast range of habitats, from forests and deserts to caves and seabed mud.
Population of Vertebrates vs Invertebrates
Nearly 2 million species have been identified till date as invertebrates. These 2 million species make up about 98% of the total animals identified in the entire animal kingdom, i.e., 98 out of 100 types of animals in the world today are invertebrates. On the other hand, vertebrates only form 2 % of the animal species. Human beings are vertebrates.
Differences in Classification
Vertebrates are classified into fish, amphibians, reptiles, birds, and mammals. In contrast, invertebrates include sponges, coelenterates (Ctenophora or comb jellies; and the Cnidaria or coral animals, true jellies, sea anemones, sea pens, and their allies), echinoderms (starfish, sea urchins, sea cucumbers), worms, mollusks (squid, octopus, snails, bivalves), and arthropods (insects).
Differences in Size
One of the noticeable differences between vertebrates and invertebrates is their size. Invertebrates such as worms, shellfish, and insects are small and slow moving because they lack effective ways to support a large body and the muscles need to power it. But there are a few exceptions like the squid which may be close to 20 meters in size. Vertebrates have a versatile support system. As a result, vertebrates have the capability to develop faster and bigger bodies than invertebrates.
Adaptation to the environment
In contrast to invertebrates, vertebrates have a highly developed nervous system. With the help of a specialized nerve-fiber system they can react very quickly to changes in their surroundings, giving them a competitive edge. Compared to vertebrates (animals with backbones), most invertebrates have simple nervous systems, and they behave almost entirely by instinct. This system works well most of the time, even though these animals cannot learn from their mistakes. Moths, for example, repeatedly flutter around bright lights, even at the risk of getting burned. Notable exceptions are octopuses and their close relatives, which are thought to be the most intelligent animals in the invertebrate world.
Similarities between vertebrates and invertebrates
The feature uniting all chordates (all vertebrates and some invertebrates like fish) is that at some stage in their lives, all have a flexible supporting rod, called a notochord, running through the length of their bodies. In a majority of chordates, the notochord is replaced by a series of interlocking bones called vertebrae during their early development. These bones form the backbone, and they give these animals their name—the vertebrates—and the others without backbone—invertebrates.
Evolution of Invertebrates
The invertebrates, in being multicellular organisms, represent several steps along the road to the organizational complexity that makes most organisms what they are today. The first life evolved in the form of single cells in water. Invertebrates were the initial few examples of multi cellular organisms that evolved in water. Invertebrates set the path for the evolution of other organisms as simple transformations started taking place. These simple changes led to complex beings in the form of vertebrates.