Kingdom Animalia-Classification, Characteristics & Examples

The classification of the animal kingdom or the Kingdom Animalia, based on characteristics, along with examples is as follows:

• Vertebrates – animals with a backbone and skeleton system
  • Pisces (Fishes) – Rohu and Shark
  • Amphibia – Toads and frogs
  • Reptiles – Snake and Lizard
  • Aves (Birds) – Peacock and sparrow
  • Mammals – Elephant, lion, and whale

• Invertebrates – animals without a backbone
  • Porifera (Porous animals) – Sponges and Sycon
  • Coelenterata or Cnidarians (Hollow sac animals) – Hydra and Sea Anemone
  • Helminths (Flatfworm and Roundworms) – Tapeworm and Ascaris
  • Annelida (Segmented worms) – Earthworms, and Leech
  • Arthropoda (Joint-footed animals) – Butterfly, Cockroach, and Scorpion
  • Mollusca (Soft-bodied animals) – Snail and Octopus
  • Echinodermata (Spiny-skinned animals) – Starfish and Sea Urchin

TOPICS COVERED:

• Introduction
• Common features of animals
• Classification of the Animal Kingdom
  • Vertebrates
  • Invertebrates
• Other Criteria for Classification of the Animal Kingdom

1.0 INTRODUCTION

There are 8.7 million living organisms on the planet Earth. Out of these, mankind has studied and classified approximately 1.3 million as of date. The Animal Kingdom or the Kingdom Animalia comprises 76% of the total species studied to date. In numbers, it comes out to be nearly 988,000. Isn’t it large?

Animals exhibit great diversity in characteristics. Some of them are as small as an ant and then there are others as large as an elephant. Due to their large number and varying characteristics, it is impossible to study them individually. So, to help, all members of the animal kingdom with similar characteristics are clubbed together to form groups. We call this process – the classification of the animal kingdom or the kingdom Animalia.

In this post, we will learn about the different basis used for the classification of the animal kingdom, along with examples and characteristics of each group.

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2.0 COMMON FEATURES OF ANIMALS

Before continuing with the classification of the animal kingdom. It will be interesting for you to know that although all animals have different features, they show certain common features as well. For example,

• Animals are heterotrophic, that is, they cannot prepare their food by themselves, they feed either on plants or on other animals.
• Most animals move from one place to another, mainly in search of food or shelter. Such a movement is called locomotion.

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3.0 CLASSIFICATION OF ANIMAL KINGDOM OR THE KINGDOM ANIMALIA

The classification of the animal kingdom is carried out based on the characteristics they exhibit. For example, if you pick up a worm, it feels soft. It has no bones in its body. Whereas, fish or frog feels hard. They have bones, all joined together with a bone in their back, to keep their body in shape. Therefore, depending on the presence and absence of the backbone, animals are broadly classified into two groups – invertebrates and vertebrates.

The backbone is the long, hard bone starting from below the neck till the end of the back. It consists of small bones called vertebrae. You can feel its presence by running over your back in its center with your hand. The hard structure which you feel is the backbone.Invertebrates are those animals that have no backbone or bony skeleton. Examples of invertebrates are – Amoeba, Euglena, sea anemones, starfish, cockroaches, snails, earthworms, etc. On the other hand, vertebrates are animals that have a backbone or bony skeleton. Examples of vertebrates are – fish, frogs, snakes, lizards, birds, monkeys, cows, cats, elephants, kangaroos, humans, etc.

Likewise, there are also other characteristics, which we use for the classification of the animal kingdom. These are:

• Body type – hollow, flat, round, porous, soft, etc.,
• The temperature of blood – cold or warm,
• Type of body covering -scaled, segmented, etc.,
• Mode of reproduction – laying of eggs, giving birth to the young ones, etc.,
• Mode of nutrition – herbivores, carnivores, omnivores, and parasites.

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3.1 CLASSIFICATION AND EXAMPLES OF ANIMAL KINGDOM BASED ON THE PRESENCE OF BACKBONE – VERTEBRATES

Vertebrates are animals with a backbone or bony skeleton. Based on their varying characteristics, we further divide them into 5 groups or classes.

3.1.1 Pisces (Fishes)

Common examples of Pisces: Almost all fishes and to name a few – Rohu, shark, electric ray fish, etc.

The main features/characteristics of Pisces (or fishes) are as below:

Almost all of the animals in this group are aquatic. It means that they live in water – seawater or freshwater. Pisces possesses special characteristics that help them in surviving underwater. For example – Pisces have a streamlined body (narrow at both ends) along with fins and scales, which helps in swimming. Further, they breathe through special organs called gills, which help in the absorption of oxygen from water. Above all, Pisces are cold-blooded animals, which is the primary requirement for survival underwater. Pisces, give birth by laying eggs.

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3.1.2 Amphibia

Common examples of Amphibians: Frogs and toads

The main characteristics of Amphibians are as follows:

Amphibians are those animals, which live in water as well as on land. They possess special features, which help them to survive both in the water as well as on the land. For example – Amphibians have slimy and slippery skin, which does not allow water to penetrate their bodies. Further, they are capable of breathing through the lungs as well as the pores present in their skin. Above all, amphibians are cold-blooded animals, which is the primary requirement for survival underwater. Amphibians give birth by laying eggs in water and have two pairs of legs adapted for making long jumps and swimming.

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3.1.3 Reptiles

Common examples of Reptiles: Lizards, snakes, turtles, tortoises, crocodiles, etc.

The main features/characteristics of Reptiles are as follows:

In Latin, ‘reptiles’ mean ‘creeping or crawling animals‘. Thus, all animals, which crawl on land and have a backbone are part of this group, called Reptiles. Most of the reptiles breathe through the lungs and live on land, but some prefer water too. For example – crocodile and turtle. As they crawl on land, thus their skin is dry and their bodies are covered with scales. Almost all of the reptiles have four short legs with which they crawl on land. Exceptions are snakes – they crawl with the help of scales. As snakes are so flexible, thus people often wonder whether snakes are vertebrates or invertebrates. Snakes have bones. They have a large number of vertebrae, located at a very small distance from each other, which provides the required flexibility.

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3.1.4 Aves (Birds)

Common examples of Aves: Pigeon, sparrow, parrot, peacock, hen, duck, etc.

The main characteristics of Aves are as follows:

Aves comprises birds. They possess special features which help them in flying. Aves have a streamlined bodies along with feathers and wings, which help in flying. Their bones are hollow and light in weight. However, it is important to note that all birds do not fly. Ostrich is one such bird. Apart from mammals, they are the only warm-blooded animals. They possess scales but only on their legs and their toes. Their jaws are provided with horny beaks but have no teeth. Aves female gives birth by laying hard-shelled eggs.

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3.1.5 Mammalia

Common examples of Mammalia: Cow, dog, deer, camel, lion, elephant, rat, whale, dolphin, human, etc.

The main features/characteristics of Mammalia are as follows:

We, humans, are mammals. The unique characteristic of mammals is that they give birth to young ones (babies). Young ones suckle milk from mammary glands present in mothers. All mammals are warm-blooded animals. They breathe through the lungs. Mammals possess projecting external ears with a body covered with hairs or fur. They usually have tails and four limbs.

The whale the biggest living creature on the planet Earth, is a mammal. Whales are mammals because unlike other fishes they do not lay eggs to reproduce or breathe through gills. They give birth to young ones and breathe through the lungs like other mammals.

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3.2 CLASSIFICATION AND EXAMPLES OF ANIMAL KINGDOM BASED ON ABSENCE OF BACKBONE – INVERTEBRATES

Invertebrates are those animals that do not a backbone. Based on their different characteristics, the invertebrates are further divided into seven groups.

3.2.1 Porifera or Poriferans (Pore-bearing animals)

A common example of Porifera: Sponge

The main characteristics of Porifera or Poriferans are as follows:

Poriferans are aquatic animals, mostly found in the sea. However, some of them also occur in freshwater bodies like – lakes and rivers. These animals represent plants, as they are the only ones in the animal kingdom, which are fixed to some object or the bottom of the pond or ocean. Their body is porous, that is, they bear many tiny pores to draw water into the body cavity, and one large pore to pass it out. Poriferans obtain food from the water which passes through the pores in their body.

Wonderful video shows a large variety of sponges. Video courtesy ChangingseasTV

Poriferans may reproduce both sexually and asexually. However, most of them reproduce asexually through budding. For example – In the case of a sponge, when a small piece of sponge is broken off it is still able to survive and grow into another sponge.

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3.2.2 Coelenterates or Cnidarians (Hollow sac-like animals)

Common examples of Coelenterates or Cnidarians: Jellyfish, hydra, sea anemones, etc

The main features/characteristics of Coelenterates or Cnidarians are as follows:

Cnidarians are aquatic animals found in the sea. They have a hollow sac-like body with only one opening, that is, mouth. Their mouth is surrounded by finger-like projections called tentacles. Tentacles serve two purposes. Firstly, they help in catching food. Secondly, they provide locomotion in the form of swimming. Bodies of Cnidarians are radially symmetrical, that is, the body can be divided into two identical halves along any plane. Cnidarians may reproduce both sexually and asexually. Generally, they reproduce asexually through budding.

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3.2.3 Helminths (Flatworms and Roundworms)

This classification of the animal kingdom is further divided into two subgroups – Platyhelminthes (Flatworms) and Nematode (Roundworms).

3.2.3.1 Platyhelminthes (Flatworms) 

The main characteristics of Platyhelminthes or flatworm as the name suggest is that, that their body is thin and flat. They mostly live as parasites in the bodies of other animals. However, we can also find them in freshwater and a moist environment. Platyhelminthes can reproduce asexually and sexually, but sexual reproduction is preferable. They lay their eggs in host bodies.

A common example of Platyhelminthes: Tapeworm. The tapeworm in humans occurs in the human intestines and may gain a length of about six meters. It looks like a long ribbon with a small head-like part at the front. It absorbs the already-digested food from the human intestine.

3.2.3.2 Nematodes (Roundworms)

The main characteristic of Nematodes or Roundworms as the name suggests is that, that their body is rounded and unsegmented. Except for a few, most of them are very small organisms. Most of them live as parasites in the body of other animals, including humans. For example, Ascaris is a roundworm that lives in the small intestine of humans, commonly in children who eat unwashed hands or eat unwashed fruits and vegetables.

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3.2.4 Annelids (Segmented Worms)

Common examples of Annelids: Earthworms and Leeches.

The main characteristics of Annelids are as follows:

The main feature of Annelids as the name suggests is that, that their body is composed of rings or segments. They live in a moist environment, such as – wet soil, freshwater, swamps, etc. Annelids have a soft, moist body wall through which they breathe. They have special organs for excretion called nephridia.

Earthworms, an Annelids are so-called because they are found in soil. They help to increase soil aeration and fertility.

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3.2.5 Arthropoda (Joint-footed animals)

The main features/characteristics of Arthropoda are as follows:

• These are joint-footed animals.
• In most cases, their body is divided into three parts – head, thorax (middle part), and abdomen (lower part), and is covered by a tough outer covering called exoskeleton or chitin.

This classification of the animal kingdom is further divided into four subgroups – Crustacea, Myriapoda, Insecta, and Arachnida.

3.2.5.1 Crustacea

Common examples of Crustacea: Crabs, shrimp, lobsters, prawns, etc.

The main characteristics of Crustacea are as follows:

Most of the Crustaceans are Aquatic, living in either marine or freshwater environments. However, few of them have adapted to life on land. For example – woodlice. The body of a Crustacean consists of three parts – head, thorax (middle part), and abdomen. But, in most of them, the head and thorax are fused as one single part. They have many legs jointed to the body.

3.2.5.2 Myriapoda

Common examples of Myriapoda: Centipede, millipede, etc.

The main characteristics of Myriapoda are as follows:

Myriapoda derived their name from the word ‘myriad’ (which means ‘countless’) and ‘poda’ (which means ‘feet’). Thus, these are animals with countless feet. Myriapoda’s body is divided into many segments. Each segment consists of one or two pairs of legs. Myriapods have a single pair of antennae and, in most cases, simple eyes. However, there are certain exceptions where they have compound eyes like insects. Myriapods mainly live on land.

3.2.5.3 Insecta

Common examples of Insecta: houseflies, butterflies, ants, mosquitoes, etc.

The main features/characteristics of Insecta are as follows:

Over 90% of the animal life forms on Earth are insects with more than a million species. The body of Insecta clearly distinguishes between the head, thorax (middle part), and abdomen (lower part). The tough exoskeleton, called chitin covers their outer body. They have three pairs of jointed legs. The head bears a mouth, a pair of antennae, or feelers. Nearly, all insects give birth by laying eggs. Adult insects typically move about by walking, flying, or sometimes swimming.

3.2.5.4 Arachnida

Common examples of Arachnida: Spider, scorpion, etc.

The main characteristics of Arachnida are as follows:

There are hundreds of thousands of species of arachnids. Arachnids mainly live on land, however, there are some which are aquatic. The body of Arachnida consists of three parts – head, thorax (middle part), and abdomen. But, in most of them, the head and thorax are fused as one single part. They have four pairs of jointed legs and unlike Insecta, they don’t have antennae. No arachnids have wings, although some spiders can float on the wind using long strands of silk. Many arachnids use silk, either to catch prey or to help them reproduce. Arachnids give birth by laying eggs.

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3.2.6 Mollusca (Soft-bodied shelled animals)

Common examples of Mollusca: Snails, octopuses, pearl oysters, etc.

The main features/characteristics of Mollusca are as follows:

These animals occur in almost every habitat found on Earth. They have soft bodies that typically have a “head” and a “foot” region. Often their bodies are covered by a hard exoskeleton. They move with the help of a muscular foot. They give birth by laying eggs.

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3.2.7 Echinodermata (Spiny-skinned animals)

Common examples of Echinodermata: Starfish, sea urchins, etc.

The main characteristics of Echinodermata are as follows:

Echinoderms are marine animals, that is, they live in an ocean or a sea. Their body is rough, spiny, and radially symmetrical, that is, it can be divided into two identical halves along any plane. They crawl on the ocean floor with the help of tube feet. Echinoderms give birth by laying eggs.

4.0 OTHER CRITERIA FOR CLASSIFICATION OF ANIMAL KINGDOM

Apart from as specified above, there are also other characteristics used for the classification of the animal kingdom. These are:

4.1 Classification and Examples  of the Kingdom Animalia Based on the Temperature of Blood

Based on the temperature of blood, we classify animals into two groups – cold-blooded and warm-blooded animals. Cold-blooded animals are those whose body temperature changes with the change in the temperature of the environment. For example – frogs and toads. Warm-blooded animals are those whose body temperature remains constant with the change in the temperature of the environment. Birds and mammals are the only warm-blooded animals. For example – Humans, cats, mice, tigers, peacocks, sparrows, etc.

4.2 Classification and Examples of the Kingdom Animalia Based on Body Type

Based on body type, we can place animals in a number of groups, such as – hollow, flat, round, porous, soft, hard, radially symmetrical, etc. Examples for each group are – hollow (hydra and sea anemones), flat (Tapeworm), round (Ascaris), porous  (Sponge), soft (Frog, earthworm, snail, and octopus), hard (Cockroach, crab, and lobster), radially symmetrical (hydra, starfish and sea urchin).

4.3 Classification and Examples of the Kingdom Animalia Based on Body Covering

Based on their body covering these animals are kept in groups, such as – scales, feathers, hair or fur, etc. Examples for each group are – scales (snakes and fishes), feathers (as in birds), hairs or furs (as in mammals like cats, dogs, and cows).

4.4 Classification and Examples of the Kingdom Animalia Based on Mode of Reproduction

Still, another way for classification of the animal kingdom is based on the mode of reproduction. Animals reproduce both asexually as well as sexually. In asexual reproduction, only one parent (hermaphrodite – having both male and female sex organs) is involved, whereas sexual reproduction occurs between two different male and female parents. Animals like sponges, hydra, etc., prefer asexual reproduction by budding, although they can reproduce sexually as well. Meanwhile, most of the animals reproduce sexually by laying eggs (such as frogs, birds, and reptiles) and some others give birth to young ones (as in mammals).

4.5 Classification and Examples of the Kingdom Animalia Based on Mode of Nutrition

Animals are heterotrophic in nutrition, that is, they derive food from other organisms, as they cannot prepare their food. Heterotrophic animals may be of two types – Holozoic and Parasites.

• Holozoic animals consume whole food (animal or plant) into their body and then digest it. We call this nutrition, holozoic. Holozoic animals are of further three types –
  • herbivores – those which eat only plants. For example – horses, cows,  deer, etc.,
  • carnivores – those which eat other animals. For example – cats, lions, hyenas, etc.
  • omnivores  – those which eat both plants and animals. For example – a man.
• Parasitic animals live on other organisms (called the host) and derive nutrition in the form of pre-digested food from the host.

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