Classification of Animal Kingdom

Animal kingdom is a noteworthy categorization of living beings on the surface of the planet which is also termed as Kingdom Animalia. The members included in this category are further categorised based on some specific features into various Genus, Family, Order, Class and phyla. The presence or absence of notochord on the animal body is one of the fundamental means of animal classification. It is to be mentioned here that a notochord is made up of a substance similar to that of a cartilage and appears like a flexible rod. It is believed that if an animal gets a notochord at point of its life, then it will be considered as a chordate. 

Non – Chordates and Chordates

1. Non – Chordates

Animals that do not have the rod – like structure called the notochord in their body are termed as non – chordates. Essentially, this phylum includes the animals like marine species as well as the members of the phylum Porifera, Hemichordata, Echinodermata, Mollusca, Arthropoda, Annelida, Aschelminthes, Platyhelminthes, Ctenophora and Coelenterata. They all are considered to be a part of this non – chordates group. 

Some of the General Features of the Non – Chordates are:

a) They are basically pseudocoelomate, coelomate, triploblastic or cylindrical animals.

b) Usually their body holds a circulatory system, open in form.

c) Fertilization takes place in an eternal manner, where as some species are found to have internal fertilization.

d) The reproduction process includes both sexual as well as asexual means.

e) Among the members of the group, most of the times the sexual distinction cannot be done accurately.

f) Through the use of body surface, trachea or gills; the respiration of the non – chordates takes place.

Some of the very common examples of phylum are Saccoglossus and Balanoglossus.

2. Chordates

Animal bodies that are featured with the presence of notochord during any point of their life span are termed as the chordates. The members of this group are characterised with pharyngeal gill slits and hollow nerve cord. Some of the basic characteristics of these creatures are:

a) The chordates are divided into large number and Protochordates are one of those to be evolved at the earliest times.

b) In some animals, the presence of chordate can be found in the entire body, from head to tail; where as in some animals it is present only in the parts of their larval tail.

c) Unlike the non – chordates, these creatures have a closed circulatory system.

d) They are generally bilaterally symmetrical, coelomate and triploblastic.

e) Their body holds a post-anal tail.

Some of the important and very common examples of this phylum are: Lancelet, Amphioxus, Doliolum, Salpa and Ascidia.

Vertebrates Classification

Classification of Vertebrates

One of the important factors, taken into account while classifying the different kinds of animals in the world is the presence of spine or backbone in their body. An animal that has a backbone is called as the vertebrate animal and they are in the phylum chordata. In terms of the vertebrates, the entire notochord or a part of it is replaced by the hard bones. Vertebrates are generally classified broadly into 7 different parts that includes the following:

Vertebrates ➨  a) Mammals (Class Mammalia)

                              b) Birds (Class Aves)

                              c ) Reptiles (Class Reptilia)

                              d) Amphibians (Class Amphibia)

                              e) Bony fishes (Class Osteichthyes)

                              f) Jawless fishes (Class Agnatha)

                              h) Cartilaginous fishes (Class Chondrichthyes)

Class Pisces (Fishes)

Fish can be considered as “the gill-bearing aquatic craniate animals that lack limbs with digits”. This class has the most diverse and wide variety of vertebrates that includes near about 30, 000 species. 41 per cent of the total population lives in fresh water, 58 per cent in the marine area and the rest 1 per cent moves between these two areas. The body structure of the species generally follows the pattern of head, trunk and tail. All the fishes do not have fins which can be categorised into two parts: paired (pelvic and pectoral fins) and unpaired (anal, caudal and dorsal fins). 

Class Amphibia

Basically amphibians are the animals that live both on land and in water and are considered to have a “double life”. Ranging to almost 3, 900 species; this class of animals consists of caecilians, toads, frogs and salamanders etc. The amphibians are generally not able to generate the temperature of their bodies and their skin types limit the distribution of their residence from moist to warm climates. Both the gills and lungs are important for them as during the larval stage they breathe with gills which is replaced with lungs when reaches the adulthood. 

Class Reptilia

All the turtles, crocodiles, lizards and snakes of the earth come under this classification of animals called reptiles. There are almost 1, 000 species in the planet that are considered to be included in the Class Reptilia. They are further divided into the following ways:

Testudines (almost 3, 000 species of tortoises, terrapins and turtles).

Squamata (9, 150 species of worm lizards snakes and lizards).

Sphenodontia ( 2 tuatara species)

Crocodilia (23 species of garial, alligators, caiman and crocodiles).

Class Aves (Birds)

These are the cold blooded and bipedal feathered animals, able to maintain a constant temperature range of their body. The limbs in the front side of their body are shaped as wings and most of the animals of this class are able to fly high in the sky, although there are a few exceptions as well. Class Aves has got almost 9, 000 species altogether.

Class Mammalia

Warm blooded animals having strings of hair in the body and is able to produce milk, come under this classification. This class of animals is the only one who nourish the off springs with milk and the world has got almost 4, 000 species of mammal altogether. Human beings, Koala, cow etc are considered to be included in this category. 

In Summary

All the animals living on the earth are broadly classified into five types and animal kingdom is one of them.

The presence or absence of notochord on the animal body is one of the fundamental means of animal classification.

Vertebrates are generally classified broadly into 7 different parts.

Class Pisces (Fishes) has the most diverse and wide variety of vertebrates.