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Time to time, different scientists have tried to classify the animals. Greek philosopher Aristotle was the first to perform the animal classification.

Aristotle classified the animals, according to the criteria like body size, habits and habitats.

Classification proposed by Aristotle is known as ‘Artificial method’. Besides Aristotle, artificial method of classification was followed by Theophrastus, Pliny, John Ray and Linnaeus. Later on, ‘Natural system of classification’ was followed. Natural system of classification was based on various other criteria. By the time, system of classification based on evolution was also brought into practice. It was used by Dobzansky and Meyer. Recently, Carl Woese has also proposed the animal classification.

• Coelom means body cavity. It is situated between the body wall and the internal organs of the body.
• The coelom is formed during early embryonic life in case of multicellular animals. It is formed from either mesoderm or gut.
• Coelom when present in the body, those animals are called eucoelomate. Phylum Annelida onwards are eucoelomate animals. They are animals with true body cavity.
• Those animals in which coelom are absent are called acoelomate animals. Porifera, Cnidaria and Platyhelminthes are acoelomate animals.
• When coelom is not formed from mesoderm or gut, but formed from other tissues, it is called pseudocoelom. Only Aschelminthes animals have such coelom and hence they are called pseudocoelomate.

• Notochord is an important feature of Chordates.
• Notochord is supporting rod like structure.
• This structure is present on the dorsal side of the animals.
• It keeps the nervous tissue separated from the rest of the tissues.
• In Hemichordates, the notochord is present in the proboscis.
• In Urochordates, the notochord is present in the tail region of the free swimming larvae.
• In Cephalochordates, the notochord lies throughout the length of the body.
• In vertebrates, notochord is replaced by the vertebral column.

• During the initial embryonic period of any multicellular animal there is formation of germinal layers or germ layer.
• These germ layers give rise to new tissues in the developing animal.
• The primitive animals were diploblastic i.e. they have only two germ layers called ectoderm and endoderm.
• The higher animals are triploblastic, having three germ layers; ectoderm, mesoderm and endoderm.
• Cnidarians are diploblastic while all other animals are triploblastic.

(a) The starfish and the sea urchin shown in the figure belong to phylum Echinodermata.

(b) The body of echinoderm animal is covered with calcareous spines or ossicles/plates.

This is the substance covering the body is mostly calcium salts and compounds.

(c) Their locomotory organs are tube feet.

(1) Cockroach belongs to the phylum Arthropoda and class Insecta.

(2) Scientific reasons for placement of Cockroach in the phylum Arthropoda:

• The body is covered by chitinous exoskeleton. 
• Jointed appendages present, three pairs of walking legs and two pairs of membranous wings. 
• Body is eucoelomate, triploblastic, bilaterally segmented and segmented. 
• Respiration by spiracles and tracheal tubes.

(a) The given animal is Octopus. 

(b) It belongs to the phylum Mollusca. 

(c) p = eye, q = sucker, s = siphon and r = tentacle.

(a) These animals are included in phylum Arthropoda.

(b) The outer layer of their exoskeleton is covered by chitinous substance.

(c) Their locomotory organs are jointed paired appendages.

The standing crop in the fields can be totally ruined by insects. The locust can damage the crops when they attack in thousands at a time. The grains are also infested by variety of insects like ants, weevils, beetles, etc. Therefore, we can say that only insects compete with humans for food.

Some insects are very useful for us. We get many products from them. e.g. Honey bee, Lac insect, Silk worm, are the insects that provide us with honey and wax, lac and silk respectively. The culture experiments are done on these insects for large scale production of these substances. Butterflies help in the pollination of crops and are thus helpful for the farmers and gardeners. Lady bug beetle is an insect which acts as a natural pest control as it attacks the other harmful insect pests

In biological pest control methods it is widely used. Some insects, on the contrary are very harmful. Mosquito, bed bugs, lice are blood sucking parasites which can spread the diseases. Mosquito is a vector for dengue, filariasis and malaria. Some are biting insects that can cause wounds, some cause allergies of various kinds. The grains and crops are destroyed to great extent by the insects. In this way the insects belonging to the phylum Arthropods are harmful to health, wealth and peace of mind too.

The shortest life span: May fly – About 24 hours. 

The longest life span : Lobster (Homarus americanus) – About 100 years.

I. Grades of organization:

(1) The grades of organization mean the way an organism has different body formation.

(2) Unicellular organisms like amoeba have a single cell in the body and hence the organization in its body is called protoplasmic grade of organization.

(3) Some organisms have only cells in their body which is called cellular grade of organization, e.g. Poriferans.

(4) Some have tissues e.g. Coelenterates. They are said to have tissue grade organization. Some have organs, they are said to have organization-organ grade, e.g. Platyhelminthes. All other higher animals have organ-system grade organization.

II. Symmetry:

(1) Symmetry on the other hand shows the base of the body formation.

(2) The symmetry can be understood by taking an imaginary cut through the animal body.

(3) Based on the symmetry there can be three types.

(4) In asymmetric animals, there is no symmetry in any plane, e.g. Amoeba.

(5) The bilateral symmetry is the one in which an imaginary axis can pass through only one median plane to divide the body into two equal halves. Most of the animals have bilateral symmetry and hence their organs are arranged in symmetric way on both the sides.

(6) The imaginary cut passing through the central axis but any plane of body aan -give more than one equal half. The organs of such animals are arranged in a radius of an imaginary circle, e.g. Cnidarians and some echinoderms.

Both grades of organization and symmetry are the bases for classifying animals into different phyla.

Classification:

Kingdom: Animalia

Sub-kingdom: Non-chordata

Phylum: Porifera

Characters:

• Multicellular organisms without cell wall
• Cellular grade organization.
• Asymmetrical body
• Acoelomate

1. Collar cells

Explanation: Porifera animals are attached to the substratum. They do not show locomotion. For gathering and catching the food, they need to produce a current in the water. For this purpose, they have characteristic collar cells in their body. Germ cells and ectodermal cells are seen in all other phyla. Cnidoblasts are characteristic feature of coelenterates.

3. Earthworm

Explanation: When an imaginary plane passing through only one axis can divide the body into two equal halves, then it is called bilateral symmetry. Such symmetry is shown only by earthworm. Sponge body is asymmetrical while starfish and jellyfish are radially symmetrical.

• All chordates possess notochord in some period of their development.
• All vertebrates also have notochord during embryonic life, which is later replaced by vertebral column.
• Therefore all vertebrates are chordates.
• But some chrodate’s like Urochordata and cephalochordata do not possess vertebral column and hence they are not vertebrates.

Amphibia:

1. Amphibians can inhabit both land and water. They can survive on both environments by breathing there.

2. The exoskeleton is absent in amphibians. The skin is soft, slimy and moist.

3. Body is divided into head and trunk. Neck is absent.

4. The digits do not have claws.

5. The respiration is by skin when in water and by lungs when on land. The larvae breathe by gills. 

6. There is external fertilization at the time of sexual reproduction. 

7. The developmental stages are eggs and tadpole. Metamorphosis is seen in amphibians. 

8. Examples : Frog, Toad, Salamander, etc.

Reptilia:

1. Reptilians are terrestrial animals. Though turtle and sea snakes can stay in water, they cannot breathe in water.

2. The exoskeleton in the form of scales. Some animals have plates or scutes (e.g. tortoise and crocodile).

3. Body is divided into head, neck and trunk. 

4. The digits have claws. 

5. The respiration is only by lungs. 

6. There is internal fertilization at the time of sexual reproduction. 

7. The developmental stages are eggs and juvenile. Metamorphosis is not seen in reptiles. 

8. Examples : Tortoise, Lizard, Snake, etc.

Cyclostomata:

1. Cyclostomata are the poorly evolved first class of vertebrate animals.

2. Cyclostomata have circular jawless mouth with suckers. 

3. Paired appendages are absent in cyclostomates. 

4. Cyclostomes have soft skin which is without any scales. 

5. Endoskeleton is cartilaginous. 

6. Examples: Petromyzon, Myxine, etc.

Pisces:

1. Pisces are the better evolved class of vertebrates which is well adapted for aquatic living.

2. Pisces have mouth with upper and lower jaws. Teeth are present in the mouth. 

3. Paired and unpaired fins present in all kinds of fishes. 

4. Fishes have different types of scales on the body. 

5. Endoskeleton may be cartilaginous, or it may be bony. 

6. Examples: Shark (Scoliodoh), rays which are cartilaginous fishes and pomfret, makerel, sardines, rohu which are bony fishes.

Urochordata:

1. Urochordates have notochord in the tail region of the adult body. 

2. These animals look like small sacs. 

3. Usually urochordates are hermaphrodites. 

4. Body of urochordate is covered over by skinlike test or tunic. 

5. Examples: Herdmania, Doliolum, Oikopleura, etc.

Cephalochordata:

1. Cephalochrodates have notochord in the entire length of the body. 

2. These animals look like small fish. 

3. Cephalochordates are unisexual. 

4. Body of cephalochordate is not covered in a test. 

5. Example: Amphioxus.

Non-chordates:

1. Non-chordates are less evolved animals and are on the lower levels of evolution. 

2. Non-chordates do not have notochord. 

3. In non-chordates, there are no pharyngeal gill slits. 

4. Nerve cord, if present is double and solid. 

5. Nerve cord is located on the ventral side of the body. 

6. Heart if present is on the dorsal side of the body.

Chordates:

1. Chordates are more evolved animals and are on the higher levels of evolution. 

2. Chordates have notochord at least in some stage of development. 

3. In chordates, there are pharyngeal gill slits. 

4. Nerve cord is single and hollow. 

5. Nerve cord is located on the dorsal side of the body. 

6. Heart if present is on the ventral side of the body.

1. Studying the different animals becomes easy when they are placed under different groups. 

2. When few representative animals of the particular group are studied then the idea about other animals belonging to that group also becomes clear. 

3. The animal evolution becomes easier to follow after studying classification. 

4. The identification of animals can be done accurately. 

5. Relationship of the different animals with each other and with other groups can be understood clearly. 

6. Habitat of each animal and its role in nature is understood by classification. 

7. Various adaptations are understood by learning classification.

i. Physalia. 

(Physalia belongs to Coelenterata, all the remaining are poriferans.)

ii. Filarial worm. 

(Filarial worm is Aschelminthes remaining are Platyhelminthes.)

iii. Nereis. 

(Nereis belongs to Annelida all the remaining are Echinoderm animals.)

iv. Spider. 

(Spider is eight-legged Arachnid, remaining are insects.)

v. Amphioxus. 

(Amphioxus is Cepholochordate all the remaining are Urochordates.)

Characteristics of Chordates:

1. All chordates possess notochord and pharyngeal gill slits in at least during some developmental stage. 

2. Presence of single, tubular and dorsally located spinal cord and ventrally located heart.

I. The phyla of Non-chordata:

• Protozoa 
• Porifera 
• Coelenterata or Cnidaria 
• Platyhelminthes 
• Aschelminthes 
• Annelida 
• Arthropoda 
• Mollusca 
• Echinodermata 
• Hemichordata

II. The subphyla of Chordata:

• Urochordata 
• Cephalochordata 
• Vertebrata

i. Tortoise. 

(Tortoise is a reptile, the remaining are amphibians.)

ii. Tube feet. 

(Tube feet are locomotory organs of Echinoderms, the remaining are locomotory organs of Annelids.)

iii. Pomfret. 

(Pomfret is a bony fish, all the remaining are cartilaginous fish.)

Aves:

1. Aves are totally adapted for the aerial mode of life. 

2. Body is spindle shaped. Body is divisible into head, neck and trunk. There are two pairs of limbs. The forelimbs are modified to form wings for flight. 

3. Digits have scales and claws. 

4. The exoskeleton is in the form of feathers. 

5. Jaws are modified into a beak. 

6. Birds are oviparous. The eggs hatch into nestlings. 

7. The incubation of eggs and feeding of nestlings is done by both parents. 

8. Examples: Crow, Sparrow, Peacock, Parrot, Pigeon, Duck, Penguin, etc.

Mammalia:

1. Mammals are adapted for terrestrial life. 

2. Body is not spindle shaped. It is divisible into head, neck, trunk and tail. There are two pairs of limbs. They are adapted for walking or running on the ground.

3. Digits have nails or hoofs. Few have claws. 

4. The exoskeleton is in the form of fur, hair, wool, etc. 

5. Jaws have teeth and they surround the mouth. 

6. Mammals are viviparous. They give birth to live young ones. (Exception: Platypus) 

7. Parental care is shown only by mother, who feeds, the babies with milk from mammary glands. 

8. Examples: Cat, Dog, Tiger, Lion, Elephant, Human, Kangaroo, Dolphin, Bat, etc.

Leech, Phylum Annelida.

Kingdom: Animalia

Phylum: Chordata

Subphylum: Vertebrata

Class: Pisces

Subclass: Elasmobranchii (Cartilaginous)

Example: Scientific name: Scoliodon sorrakowah. 

Common name: Shark

Distinguishing characters of Echinodermata:

1. Marine organisms with skeleton made up of calcareous spines. Calcareous material on the body hence the name is Echiodermata. Some are sedentary while some are free swimming.

2. Body is triploblastic, eucoelomate and radially symmetrical when adult. The larvae are bilateral symmetrical.

3. Locomotion with the help of tube-feet which are also used for capturing the prey.

4. Echinoderms have regeneration capability. 

Hence they can restore their lost parts.

5. Most of them are unisexual.

6. Examples; Starfish, sea-urchin, brittle star, sea cucumber, etc.

(1) Mollusca – Mantle 

(2) Hemichordata – Trunk.

The living organisms are classified according to their basic characteristics, such as presence or absence of nucleus, unicellular body or multicellular body, presence or absence of cell wall and the mode of nutrition in them.

I am Ascaris. I am included in Aschelminthes.

The plants are classified according to the following basis:

1. Presence or absence of the organs. 

2. Presence or absence of separate

Ghariyal and crocodile are reptiles. They can swim in water and crawl on land. But they can respire only with the help of lungs. Their breathing is through nostrils. Even when in water, they have to inhale and exhale by coming up to the surface of water for air. Amphibians can breathe through the skin when in water and by lungs when on land. They also have hard exoskeleton which amphibians do not have.

Hence, ghariyal and crocodile are not amphibians, but they are reptiles.

Starfish. I am from Echinodermata phylum.

i. (b) Snake

ii. (d) starfish

iii. (c) Jointed appendages