Animalia Kingdom - Classification of Living Beings

Kingdom Animalia is one of the significant divisions among the five kingdoms' classification of living beings. In, Kingdom Animalia, there are two major classifications. They are Vertebrates and Invertebrates.

Kingdom Animalia - Classification of Living Beings

Animalia Kingdom is basically subdivided into vertebrates and invertebrates.

Vertebrates: Vertebrates are animals with a vertebral column (backbone) in their body

Invertebrates: Invertebrates are animals without a vertebral column (backbone) in their body.

Classification of Invertebrates

According to the five-kingdom classification, invertebrates are classified into eight phyla. They are:

Porifera
Coelenterata
Platyhelminthes
Nemathelminthes
Annelida
Arthropoda
Mollusca
Echinodermata

Porifera

Porifera is the first multicellular animals. They have numerous holes in their body called ostia. They also have one big hole called the osculum. The phylum Porifera are aquatic animals that are found sticky to the beds of seas and oceans. The water enters the body through the Ostia and exits from the osculum.

Characteristics of Phylum Porifera

The followings are the characteristics of Porifera Phylum:

Porifera are the first multicellular animals.
No development of tissue.
Phylum Porifera has diploblastic bodies as they develop from the germ layer (two layers).
They respirate from the surface of the body.
They are found sticky to some objects inside the water.
These animals have high regeneration capacity. When their body gets fragmented, a new body forms from the fragment.
They undergo sexual as well as asexual reproduction. Asexual reproduction takes place by budding and regeneration whereas gametes are produced by the animals for sexual reproduction.
The bodies of these animals are radially symmetrical. They can be formed into two equal divisions by cutting them from any direction.

Examples – Sponge, Hylonema, Cliona, Leucosolenia, etc. are the animals that fall under phylum Porifera.

Coelenterata

Animals with hollow bodies and tentacles are classified into the phylum Coelenterata. The tentacles are used to transport the food into the mouth and are also used for transportation. They are named after the word coelenteron, which means the room (hollow) inside the body.

Characteristics of Phylum Coelenterata

These are the characteristics of animals of phylum Coelenterata:

They are multicellular animals with diploblastic bodies.
Animals of phylum Coelenterata are the first tissue-graded animal. They have a hollow room inside their body, known as a coelenteron. Coelenteron helps in digestion. So, they are also known as gastrovascular cavities.
There is only one opening in their body, which is surrounded by the tentacles. Tentacles help them to move and supply food to the mouth. Tentacles are also used to kill the prey.
They respirate from the surface of the body.
They reproduce by sexual and asexual methods. An asexual method is budding (formation of buds) and regeneration.
They are found on the surface of lakes, ponds, and oceans. They have a radially symmetric body.

Examples – Hydra, Coral, and Jelly Fish

Platyhelminthes

Animals in phylum Platyhelminthes are parasites. They have flat bodies like tape or a leaf. Platy means flat and helminths mean insects. So, they are known as flat insects. They depend upon the host cell and are attached to the host cell.

Characteristics of Phylum Platyhelminthes

Animals of phylum Coelenterata possess the following characteristics.

They have flat-shaped bodies like tape or leaves. So, they are known as flat insects too.
Bodies of Platyhelminthes are developed from three layers, so they have triploblastic bodies.
They have a mouth in the front part (anterior part) or a downward surface (ventral surface) but they do not have an anus. They have hooks around their mouth by the help of which it is attached to the host cell.
Their mouth is developed into suckers, which suck the blood or food from the host cell.
Groups of organs can be seen but no full development of the system is seen.
They have tissue name parenchyma between the walls of their body and the organs. It helps in transportation. They don’t have a blood circulation system.
They respirate from the surface of the body.
They are hermaphrodite animals. It means they have both male and female reproductive organs in the same body. Internal reproduction takes place.
They reproduce by sexual as well as asexual methods. Fragmentation and regeneration are the methods of asexual reproduction.
Most of them are endoparasites, and some of them are free-living animals.

Examples – Liver Fluke, Tape Worm, Blood Fluke, etc.

Nemathelminthes

Animals in this phylum have a long and cylindrical bodies with pointed ends. They suck blood from other animals and humans.

Characteristics of Phylum Nemathelminthes

Following are the characteristics of animals that fall inside Phylum Nemathelminthes.

They have a long and cylindrical-shaped body with pointed ends.
They have a bilaterally symmetrical body. Their body can be divided into two equal parts.
They have a triploblastic body.
They have sucking organs, mouth, and anus with complete development of the digestive system.
There is no development of respiratory and circulatory systems. They respirate through the surface of the body.
They are unisexual animals.
They only reproduce by sexual methods. Reproduction is internal.
Most of them are parasites while some of them are free living. Parasites are responsible for causing disease.

Examples – Ascaris, Hookworm, Pinworm, etc

Annelida

Animals of phylum Annelida have long, rounded, and fragmented bodies. They are usually found in moist places.

Characteristics of Phylum Annelida

Here are some of the Characteristics of animals of phylum Annelida.

They have a bilaterally symmetrical and triploblastic body.
They have moist skin.
They respirate from the surface of the body.
They have developed nephridia for the ejection.
They have developed a circulatory system. Blood contains Haemoglobin.
They have a well-developed digestive system.
Some of the Annelida are hermaphrodites and some of them are unisexual animals.
They have high regeneration capacity.
They have developed a nervous system along with a nerve ring.
Some of the Anneliada are found in most places and water, while some of them are found as external parasites.

Examples – Earthworm, Leech, Nereis, etc.

Arthropoda

Arthropoda is the largest phylum of Animal Kingdom. They are terrestrial, aquatic, and well as aerial animals. All Arthropods have jointed legs.

Characteristics of Phylum Arthropoda

The following are characteristics of Phylum Arthropoda.

They have fragmented bodies and jointed legs.
The bodies of arthropods are covered by a hard surface known as an exoskeleton. These are formed by chitin.
They have bilaterally symmetrical and triploblastic bodies.
Most of the Arthropods have compound eyes, an antenna, and mouth parts in their head.
They are unisexual animals and only reproduce by sexual methods.
They are found in air, water, and land and respirate through the skin. gills or trachea.
They have developed circulatory, muscular, nervous, and digestive systems. They also eject.
Bodies of Arthropods are divided into three parts. They are the head, thorax, and abdomen.

Examples – Butterfly, Crab, Spider, Centipede, etc.

Mollusca

Mollusca is the seventh phylum in the classification of the invertebrates. Some of the animals of the Mollusca phylum are found in moist places and some of them are found in seas and oceans. They have tentacles around their head and their legs are developed from muscles, which helps them in transportation.

Characteristics of Phylum Mollusca

Following are the characteristics of Phylum Mollusca.

They have a soft body. The body is divided into the head, visceral mass, muscular foot, and mantle.
Most of the Mollusca have a protective shell made up of calcium. They hide inside their shell in case of any danger.
They have eyes along with tentacles in the head.
They have an asymmetrical body, which can’t be divided into two parts.
The muscular foot helps in transportation.
They respirate through the surface of the body, gills, or pulmonary sac.
They have developed Circulatory System, Digestive System, and Nervous System in their body.
Most of them are unisexual while some of them are hermaphrodites.
They are found in both land and water.

Examples – Slug, Snail, Octopus, etc.

Echinodermata

Animals in this phylum have spiny skins. They are mostly found in seas and oceans.

Characteristics of Phylum Echinodermata

Following are the characteristics of Phylum Echinodermata.

Their bodies are covered by spiny shells, made up of calcium carbonate.
They do not have distinct heads.
They have a triploblastic and radially symmetrical body.
They transport with the help of tube feet.
They have developed digestive systems.
They undergo sexual reproduction.
They also have regeneration capacity.
They respire through the help of gills.
They have star-shaped, round, or flat bodies.

Examples – Starfish, Sea Cucumber, Sea Urchin, etc.

Classification of Vertebrates

There is only one phylum in the vertebrates.

Phylum: Chordata

Most developed animals of the Animal Kingdom fall in this phylum. All the animals with notochord are divided into this phylum.

Characteristics of Phylum Chordata

Following are the major characteristics of animals of phylum Chordata

They have developed notochord.
The skeleton system is covered by the muscles.
They have a closed circulatory system.
They have developed gill silts around the external neck during the fetus condition.
The hollow part inside the vertebrae is filled with tube-like nerves.

Phylum Chordata is also divided into four subphylum. They are:

Hemichordate
Eurochordata
Cephalochordate
Vertebrata

The first three subphyla are also called primary Chordata or protochordate. They are less developed than the last subphyla vertebrate.

We will only learn about subphyla Vertebrata.

Sub Phylum- Vertebrata

All the animals of vertebrates have a vertebral column (backbone). The initially developed notochord in these animals is later displaced by the vertebral column. These are the most developed animals. Some of the characteristics of this subphylum animals are similar while some of them are different.

Characteristics of subphylum Vertebrata

Following are the characteristics of the subphylum Vertebrata.

They have a bilaterally symmetrical body.
Respiration takes place through the skin, gills, or lungs.
Those animals whose body temperature changes according to the surrounding temperature are called cold-blooded animals, and those animals whose body temperature doesn’t changes according to the surrounding temperature are called warm-blooded animals.
They have well developed circulatory system, with a heart that is two to four-chambered.
They reproduce by producing eggs or direct reproduction.
Oviparous – Those who reproduce by producing eggs.
Viviparous – Those who directly give birth to infants.

Based on the similarity in characteristics, body structure, and reproduction, Vertebrata is further divided into five classes. They are:

Pisces
Amphibia
Reptilia
Aves
Mammalia

Class – Pisces

Those animals that fall in the class Pisces are aquatic animals with streamlined bodies and spines on their skins.

Characteristics of Class pieces

Following are the characteristics of class Pisces.

Streamlined body with spiny skins.
The bodies of pieces are divided into head, trunk, and tail. They do not have a neck.
They respire through gills, which are developed on both sides of the head.
They are aquatic animals and they can swim with the help of the pairs of fins.
They have air sacs inside their body.
They are unisexual animals.
They are poikilothermic animals.
They have two-chambered hearts.
Some of the Pisces are oviparous and some of them are viviparous.
Most of the Pisces undergo external fertilization while some of the Pisces undergo internal fertilization.
Examples – most types of fish, sea horses, etc.

Class – Amphibia

The animals that live in both land as well as water are classified into this class and they are also called amphibians.

Characteristics of Class Amphibia

Following are the classification of Amphibians.

Bodies of amphibians are covered by moist skins.
The body of an amphibian is divided into two parts. They are head and back. Some amphibians also have tails.
They have four limbs.
They are poikilothermic animals.
They respire through gills during the tadpole stage and they respire through skin or lungs during the adult stage.
Amphibians have three-chambered hearts.
They are unisexual animals.
They are oviparous animals. They lay eggs in water. They undergo external fertilization.
Water is required for reproduction.
Examples – Frog, Toad, Salamander, etc.

Class – Reptilia

Animals that fall under this class are called reptilians. They might be aquatic or terrestrial. They move by crawling and are cold-blooded animals.

Characteristics of Class Reptilia

Following are the characteristics of class Reptilia.

The body of the reptilians is dry and covered by dry and thorny scales.
The body of reptilians can be divided into four parts. They are the head, neck, back, and tail.
They are poikilothermic animals.
They respire from the lungs.
They are unisexual, oviparous, and undergo internal fertilization.
They have three-chambered hearts, except the crocodile. Crocodiles have four-chambered hearts.
Some of them live in water and some of them live in land. They respire in lands.
Examples – Snakes, Tortoise, Crocodile, etc.

Class – Aves

Aves are those animals whose forelimbs are transformed into wings. They have pointed mouths called beaks or bills. The body of the Aves is covered by feathers.

Characteristics of Class Aves

Following are the characteristics of class Aves.

The body is divided into the head, neck, body, and tail.
The forelimbs are transformed into wings for flying and hind limbs are used to walk.
They are homeothermic animals.
They respire with the help of their lungs.
They have a four-chambered heart.
They are unisexual, oviparous, and undergo internal fertilization.
They have hollow bones and air sacs in their body which helps them to fly.
Examples – Most the birds

Class – Mammalia

Mammals are those animals, whose bodies are covered by furs, they give birth and also breastfeed the babies.

Characteristics of Class Mammalia

Following are the characteristics of class mammalia.

The bodies of mammals are covered by fur.
Most mammals’ bodies are divided into head, body, tail, and neck.
They have mammary glands.
They respire with the help of their lungs.
They are not homeothermic animals.
They have a four-chambered heart.
They are unisexual, viviparous, and undergo internal fertilization.
Examples – Man, Cow, Horse, Whale, etc.