Do you've any idea about how many animal species are there on Earth? There are as many as 30 million animal species alive. It always excites a person to learn more about these species, but it's quite a challenging task too. As there is enormous number of species, it becomes tough to bear in mind each one of them. So, to have a clearer idea, you could segregate these species of animals into 6 standard classes.

The first class of animals is invertebrates. As the name suggests, these animals lack a spine or vertebral column. Those of you fighting with back pain might be wishing that you were an invertebrate too. Some species that fall into this category encompass flatworms, insects, micro-organisms and the like. 97% of the animals alive today are invertebrates.

Fishes is another animal group. They were the first vertebrates to evolve. Fishes could be broadly classed into cartilaginous fish, ray finned fish and lobe finned fish. Amongst the three, it is ray finned fish that's the most versatile and has 24,000 species. If you want an additional pet along with your pet dog, then fishes are a brilliant selection.

Another group is one of the amphibians that live both- in the water and on the land. Nearly 370 million years ago, 1st amphibian species developed from lobe finned fishes. Frogs, salamanders and many more fall in this category. Besides this, 5,000-7,000 amphibians were alive.

One of the most crucial categories of species of animals is Reptiles. These cold blooded vertebrates exhibit two varying features. One of their features is that they have scales all over their body and the other is that they produce hard eggs. First amphibian came into existence 340 million years ago. Some of the common amphibians are crocodiles, tuataras, squamates, turtles, etc.

Mammals is perhaps the most developed category of animals. They inhibit a diverse array of characteristics and can adjust themselves to a wide variety of habitats. There are at least 5,400 species of animals alive today. Mammals are extremely diverse. They range from the tiny Bumblebee Bat, which is three centimeters to the blue whale, which is 33 cm long. Did you know that humans are also mammals?

When we chat about animals, we also chat about birds. There are a lot of birds which are animals and that can also fly. Moreover, birds have specific characteristics that make them different from the others. These features are furcula, feathers, bills, etc. Flying birds give a feel of happiness. Therefore, bird watching is a hobby for lots of people. You can also enjoy bird watching, with no worries regarding sun tan.

Gaining knowledge about species of animals is an enriching experience for sure.

Here are a few more ways to know about Suffering From Back Pain and Pet Dog.

Author's Bio: 

I am a yoga trainer who has been teaching various yoga poses for more than 10 years now.