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                                 INTRODUCTION

Classification is the process by which anything is grouped in to convenient categories based on some easily observable character.  Since the down of civilization, there have been many attempts to classify living organisms.  It was done instinctively not using criteria that were scientific but borne out of a need to use organisms for our own use-for food, shelter and clothing.  Aristotle was the earliest to attempt a more scientific basis for classification.  He used simple morphological characters to classify plants into trees, shrubs and herbs.  He also divided animals into two groups, those which had red blood and those that did not.

            In R.H Whittaker (1969) proposed a five kingdom classification.  The kingdoms defined by him were named Monera, Protista, Fungi, Plantae and Animalia.   The main criteria for classification used by him include cell structure,   thallus organization mode of nutrition reproduction and phylogenetic relationship.  The five kingdom classification to understand the issues and consideration that influenced the classification system

 

    

 

          

 

 

 

                                Five Kingdom Classification

                 Organisms are divided into five major kingdoms. R.H Whittaker proposed the five kingdom classification in 1969. The most common system of classification in use today is the Five Kingdom Classification. In this system all living organisms are divided into five kingdoms: The classification of living organisms according to Whittaker into five kingdoms namely are as follows: 

KINGDOM: MONERA 

KINGDOM: PROTISTA 

KINGDOM: FUNGI 

KINGDOM: PLANTAE

KINGDOM: ANIMALIA

                                           KINGDOM MONERA 

Monera are considered as the most primitive group of organisms. They include various types of bacteria and blue-green algae. Monera are most abundant of all organisms, due to their versatility of their habitat. It is estimated that a single drop of water contains 50 billion bacteria. Kingdom Monera - All the organisms of this kingdom are prokaryotes. Complex structure was the basis of classification of organisms, many centuries ago. According to R.H. Whittaker's five kingdom classification all the bacteria were placed under the Kingdom Monera.

Bacteria are grouped under four categories based on their shape: the spherical coccus, the rod shaped bacillus, comma-shaped Vibrium and the spiral Spirillum.Though the bacterial structure is very simple, they are very complex in behavior. Compared to many other organisms, bacteria as a group show the most extensive metabolic diversity. Some of the bacteria are autotrophic, i.e., they synthesize their own food from inorganic substrates. They may be photosynthetic autotrophic or chemosynthetic autotrophic. The vast majority of bacteria are heterotrophs, i.e., they do not synthesis their own food but depend on their organisms or on dead organic matter for food.

                               CLASSIFICATION OF KINGDOM MONERA

The kingdom Monera includes organisms that are single-celled known as bacteria. The kingdom is divided into two groups Archeobacteria and Eubacteria. All the organisms of this kingdom are prokaryotes. These cells do not have nuclear membrane, the chromosome is a single and circular, they also lack membrane bound cellular organelles. This kingdom includes bacteria, cyanobacteria, mycoplasma etc. They are unicellular organisms and they can be either aerobic or anaerobic.

Kingdom Monera are classified into two groups:-

1.     Archeobacteria

2.     Eubacteria

   

                       ARCHEOBACTERIA

Archeobacteria are microbes that live in extreme and harsh condition, they are known as extremophiles. These bacteria lack cell wall, their cell membrane is made of different lipids and their ribosomes are similar to that of Eukaryotes. Methanogens are present in the gut of several ruminant animals such as cows and buffaloes and they are responsible for the production of methane from the dung’s of these animals.

                            EUBACTERIA

Eubacteria are true bacteria. The characteristic features is the presence of rigid cell wall and if present a motile flagellum that aids in locomotion. These organisms are characterized based on their nutrition and their shapes.  The cyanobacteria have chlorophyll “a” similar to green plants and are photosynthetic autotrophs. Based on the mode of nutrition bacteria are broadly classified into Autotrophic and Heterotrophic.

1.     AUTOTROPHIC BACTERIA

Autotrophic bacteria- Bacteria which prepare their own food are autotrophic. It can be chemosynthetic or photosynthetic.

Chemosynthetic bacteria: - chemosynthetic bacteria are those which prepare their food with the help of inorganic substrates.

Photosynthetic bacteria: - photosynthetic bacteria are autotrophic bacteria which prepare their own food by the process of photosynthetic.

Cyanobacteria: - They have chlorophyll similar to plants and hence they are photosynthetic autotrophs. The marine and terrestrial and they may be unicellular, colonial or filamentous. The colonies are surrounded by gelatinous sheath. They can also fix atmospheric nitrogen. (Eg: Nostoc and Anabaena).

Chemosynthetic autotrophs: - these organisms oxidize substances like nitrites, nitrates, ammonia etc. The help in recycling substances like nitrogen, sulphur, iron etc.

     2.  HETEROTROPHIC BACTERIA

Heterotrophic bacteria are those which are dependent on other organism either directly or indirectly for their nutrition. They are most abundant and are important decomposers. Some are helpful in curdling milk, production of antibiotics, in nitrogen fixation and some are pathogens. Causing damage to human beings, crops, citrus, canker are well known diseases caused by bacteria. Heterotrophic bacteria can be parasitic and saprophytic. Saprophytic bacteria feed on dead and decaying matter.  Reproduction in bacteria is mainly by fission. Under unfavorable conditions they reproduce by spores. Sexually bacteria reproduce by a primitive mode of DNA transfer from one bacterium to another i.e., by conjugation, transduction or transformation. Mycoplasmas are the known to be the smallest living cells. They completely lack cell wall and can survive without oxygen. Most of the mycoplasma is pathogenic in nature in animals and plants. 

                                          

                                      KINGDOM PROTISTA

All single celled organisms are placed under the Kingdom Protista. KingdomProtista is a diverse group of eukaryotic organisms. Protista are unicellular, some are colonial or multicellular, they do not have specialized tissue organization. The simple cellular organization distinguishes the protists from other eukaryotes. The cell body of the protists contain have a nucleus which is well defined and membrane bound organelles. Some have flagella or cilia for locomotion. Reproduction in protists is both asexual and sexual. They live in any environment that contains water.

Chrysophytes: - There are three types of golden-algae: yellow-green algae, golden brown algae, diatoms. Diatoms are the most abundant and are found in seawater and freshwater habitats. The shell of diatoms is made of silica. They are major source of food to may aquatic organisms. The shells of fossil diatoms form thick deposits on the sea floor known as 'diatomaceous earth'. It is used as water filters, abrasive and to add sparkling to products such as paint and fingernail polish. 

Slime Molds: - Slime molds are saprophytic protists. They live in moist soil, decaying plants and trees. They are single-celled organisms. During favorable condition they form multicellular aggregations called plasmodium. During unfavorable conditions, plasmodia differentiate to form fruiting bodies bearing spores at the tip. These spores’s posse’s resistant true walls.

Dinoflagellates: -These spores disperse by air currents.  These organisms are mostly marine and photosynthetic. They appear yellow, green, brown, blue or red depending on the main pigments present in their cells. The cell wall has stiff cellulose plates on the outer surface. Most of them have two flagella; one lies longitudinally and the other transversely in a furrow between the wall plates. Very often, red flagellates (Examples: Gonyaulax) undergo such rapid multiplication that they make the sea appear red (red tides).Toxins released by such large numbers may even kill other marine animals such as fishes.

Euglenoids: - Majority of them is fresh water organisms found in stagnant water. Instead of a cell wall they have protein rich layer called pellicle which makes their body flexible. They have two flagella, a short and a long one. Though they are photosynthetic in the presence of sunlight. When deprived of sunlight they behave like heterotrophs by predating on other smaller organisms. (Example: Euglena).

Protozoan’s: -All protozoans are heterotrophs and live as predators or parasites. They are four major groups of protozoan.

        i.            Amoeboid protozoan: - These organisms live in fresh water, sea water or moist soil. They move and capture their prey by putting out pseudopodia.

     ii.            Flagellated protozoan: - The members of this group are either free-living or parasitic. They have flagella. (Eg: Trypanosome).

   iii.            Ciliated protozoan: - These are aquatic, actively moving because of the presence of thousands of cilia. (Eg: paramecium).

   iv.            Sporozoans: This includes diverse organisms that have an infectious spore-like stage in their life cycle. (Eg: plasmodium)

                                

                     

                          KINGDOM FUNGI

The organisms in kingdom fungi include mushrooms, yeast, molds, rust, smuts, and puffballs, truffles, morels, and molds. Mycology is a discipline of biology which deals with the study of fungi. Fungi appear like plants but are closely related to animals.  Fungi are in a wide variety of sizes and forms and have great economic importance. Fungi show a great diversity in morphology and habitat. Fungi are heterotrophic organisms; they obtain their nutrients by absorption. The cell wall of fungi is mostly made up of carbohydrate chitin, while the cell wall in plants is made of cellulose. The carbohydrates stored in fungi are in the form of glycogen. The 'fruit' body of fungus is only seen, while the living body of the fungus is a mycelium, it is made of tiny filaments called hyphae. The mycelium is hidden. Nutrition in fungi is by absorbing nutrients from the organic material in which they live. Fungi do not have stomachs, they digest their food before it pass through the cell wall into the hyphae. The hyphae secret enzymes and acids that break down the organic material into simple compounds. The walls of fungi are composed of chitin and polysaccharides.

Most fungi are heterotrophic and absorb soluble organic matter from dead substrates and hence are called saprophytes .Those that depends on living plants and animals are called parasites. They can also live as symbionts in association with algae as lichens and with roots of higher plants as mycorrhiza.

Reproduction in fungi can take place by vegetative meaning fragmentation, fission and budding. Asexual reproduction is by spores called conidia or sporangiospores and sexual reproduction is by oospores.

                        Kingdom Fungi Classification

Division Ascomycotes;

The sac-fungi produce spores in small cup-shaped sacs called asci, hence the name Ascomycotes. The mature sac fungi spores are known as ascospores, they are released at the tip of the ascus breaks open. Yeast is the most common one-celled fungi. Yeast reproduces through asexual process called budding. The buds form at the side of the parent cell; they pinch-off and grow into new yeast cell which is identical to the parent cell. Examples of sac-fungi are morels, truffles, cup fungi and powdery mildews. Example: Aspergillus, Claviceps, Neurospora. 

Division  Basidiomycetes:                      

Basidiomycetes include the mushrooms, puff-balls, rusts and toadstools. The spores are borne on a club-shaped spore case called basidiaum. In mushrooms the basidia are lined at the gills under the cap. Huge numbers of spores are produced by the club fungi. In fact, an average sized mushroom produces over 16 billion spores rarely germinate or mature. Example: Agaricus, Ustilago and Puccinia.

Division Deuteromycota:

These organisms are known as imperfect fungi because they lack sexual reproduction. They reproduce by asexual spores known as conidia. Most of the fungi cause diseases to humans like ringworm, athlete’s foot. Economically important imperfect fungi are Penicillium and Aspergillus. Other examples are Alternaria, Colletotrichum and Trichoderma.

Division Phycomycetes:

Members of Phycomycetes are found in aquatic habitats and on decaying wood in moist and damp places or as obligate parasites on plants. The mycelium is aseptates and coenocytes .Asexual reproduction takes place by zoospores.

                            

                       KINGDOM PLANTAE

            There are different types of plant species, which are found on planet earth. They are sorted and classified into a separate kingdom known as Kingdom plantae. This classification is based on their similarities and differences. 

The Kingdom plantae is also called as kingdom Metaphyta. The Kingdom plantae includes all types of eukaryotic, multicellular, photosynthetic plants found in this biosphere. Most of the organism in this kingdom is autotrophs, which synthesis their own food with the help of solar energy. There are very few species, which are both autotrophs and heterotrophs. The history of life on earth and the success of many organisms literally depend on the success of plants. The Kingdom plantae can be defined as multicellular, autotrophic eukaryotes, which conduct photosynthesis. All member of this family comprises of true nucleus and advanced membrane bound organelles. They are quite different from animals.

                          Kingdom Plantae Classification

The Kingdom Plantae contains about billion types of plants species and it was very difficult to identify different types of species. Many biologists contributed in classifying different plants species in to their separate kingdom.

Based on their classification, plants are divided into the four main groups. These classifications was based on

• The presence of vascular tissue.
• The absence of vascular tissue.
• The presence of seeds.
• The absence of seeds.

Vascular tissue and the seeds are mainly considered as they play a vital role in:

Vascular tissue helps in transporting substances (water, minerals and sugars) throughout the plant.

Seeds are structures, which contains an embryo that helps in storing food.

Phyllum Bryophyte

• They are non-vascular land plants, which do not contain any conducting tissues and are often referred to as bryophytes. 
• These plants are small, grow close to the ground and include mosses and liverworts.
• They are very small in structure and are considered as important members of our ecosystem.
• The reproduction process is carried in their spores. They are non flowering plant and are found mainly growing on the ground, on other plants and on rocks.
• They play a vital role in preventing soil erosion.

Phylum bryophyte (e.g.: Mosses, Liverworts and  Hornworts).

Phylum Pteridophyta

·        They are seedless vascular plants, which contain vascular tissues but do not produce seeds.  

·        They are involved in transportation of fluids.

·        The reproduction process is carried by spores. 

Phylum Pteridophyta (e.g.: horsetails, ferns and club mosses).

Phylum Angiosperm

Angiosperms are flowering plants, which develops the seeds within a protective structure.

·        The reproduction process is carried by Angiosperm.

·        They develop their seeds within an ovary, which itself is embedded in a flower. After the stage of fertilization, the flower falls and the ovary bulges to become a fruit.

·        Angiosperms in the class Dicotyledoneae grows into two seed-leaves (cotyledons).

·        An angiosperms leaf consists of a single, branched, main vein, which originates from the base of the leaf blade. In few plats, it may also consist of four or more main veins diverging from the same base.

Phylum angiosperms (e.g.: trees, shrubs, vines and flowers).

Phylum Gymnosperm

Gymnosperms are non-flowering plants with undeveloped seeds, which are present in enclosed structures.

Monocot begins with a single seed-leaf.  The main veins of their leaves are usually parallel and unbranched. 

Monocot plays an important role in providing us with our primary sources of nutrition, which includes grains, fruits, etc.

Phylum gymnosperms (Eg:  palms, carpet lawns, etc).

                   

                         

 

 

 

 

 

                                                                                                

                          KINGDOM ANIMALIA

The major group of animals is classified under the Kingdom Animalia, also known as Metazoan. This kingdom does not contain prokaryotes. All the members of this kingdom are multicellular, eukaryotes. They are heterotrophs; they depend on other organisms directly or indirectly for food. Most of the animals ingest food and digest in the internal cavity. Animals are divided into various sub-groups; biologists have identified about 36 phyla within the animal kingdom including birds, mammals, reptiles, fish, amphibians etc.   The Kingdom Animalia is characterized by eukaryotic and heterotrophic organisms. They are multicellular and lack cell wall. They depend directly or indirectly of plants for their food. Food is ingested and digested in their internal cavity and food reserves are stored as glycogen or fat. Nutrition is holozoic, i.e., by ingestion of food. Animals follow a definite growth pattern; the adults have a definite shape and size. Higher forms of animal’s exhibit well developed sensory and neuromotor mechanism. Most of the organisms are capable of locomotion. Reproduction is by copulation of male and female which is followed by development in embryonic stages. 

                                  Animal Kingdom Classification

Animals are characterized being multicellular and eukaryotic. Classification of animals is about organizing organisms into groups. Members of a group have shared characteristic, that is common to all members of that group and it is this character that defines the group.

 There are about 1.2 million species of animals identified and there are almost 9-10 million species of animals on earth. This huge population of animals creates importance for the need of classification. Classification helps in assigning a systematic position to newly described species. 

                              

                                   Basis of Classification

There is a difference in structure and form of different animals, there are a few fundamental characteristics that are common to various organisms. The features are 

·                     Arrangement of cells,

·                     Body symmetry, 

·                     Nature of coelom

·                     Patterns of digestive, circulatory and reproductive systems,

·                     Arrangement of cells in germ layers,

·                     Segmentation,

Levels of Organisation 

All the organisms of the Animal kingdom are multicellular but they do not exhibit the same pattern if organization of cells. 

The patterns of cellular organization seen in animals are: 

·        Cellular Level of Organization- In these animals the cells are arranged in the form of loose cell aggregates. This kind of cellular organization is seen in sponges. Example: Sponges.

·        Tissue Level of Organization- Cells of the animals shows division of activities among themselves. Cells performing the same function are arranged as tissues. Example: Coelenterates.

·        Organ Level of Organization- Tissues of the animals performing the similar function is grouped to form organs. Each organ is specialized for specific function. Example: Platy helminthes.

·        Organ system Level of Organization In animals where organs have associated to form functional systems where each system is concerned with a specific physiological function are said to exhibit organ system level of organisation. Example: Annelids, Arthropods, Molluscs, Echinoderms and Chordates.  

                           

                              Patterns of Organ Systems

Organs systems in different groups of animals exhibit various patterns of complexities. 

·                     Digestive System - There are two patterns of digestive system incomplete and complete digestive system.  

 Incomplete digestive system- This pattern of digestive has only one opening to the outside of the body, i.e., a single opening serves as both mouth and anus. Example: Platy helminthes.

Complete digestive system- In this pattern there are two opening to the outside of the body, the mouth and the anus. Example: Arthropods, Chordates, etc.

·                     Circulatory System - Circulatory system may be of two types - open type and closed type.

Open type- In open type circulatory system the blood is pumped out of the heart and the cells and tissues are diectly bathed in it.

Closed type- In this type of circulatory system the blood is circulated through a series of vessels of varying diameters - the arteries, veins and capillaries.

                                                 Body Symmetry

Animals can be categorized on the basis of their body symmetry. The arrangement of body parts around a central point or line determines the symmetry.

·        Asymmetrical- some animals cannot be divided into two equal halves along any plane passing through the center of the organism. Asymmetry is the complete absence of symmetry. Example: Sponges.

·        Radial Symmetry - Animals are said to exhibit radial symmetry, when any plane passing through the central axis of the body divides the organism into two identical halves. Example: Coelentrates, ctenophores and echinoderms. 

·        Bilaterally Symmetry- Animals where body can be divided into identical right and left halves are said to be bilaterally symmetrical. Example: Annelids, Arthropods etc.

                                       Body Wall 

Body wall of animals is arranged in two or three embryonic layers. Accordingly animals are diplobalstic or triploblastic.

Diploblastic Animals - Animals in which the cells are arranged in two embryonic layers are known as diploblastic animals. Diploblastic animals have an external ectoderm and an internal endoderm. The middle mesoglea is the middle undifferentiated layer present between outer ectoderm and middle mesoderm. Example: Coelentrates.

Triploblastic Animals - Triploblastic animals are those, whose cells are arranged in three germinal layers, the outer ectoderm, inner endoderm and the third germinal layer mesoderm which is in between outer ectoderm and the endoderm. Example: Platyhelminthes to Chordates.

                                   Nature of Coelom

The presence or absence of a cavity between the body wall and the gut wall is important characteristic for classification. Coelom is the body cavity that is lined by the mesoderm. There are three types of animals based on the type of coelom - coelomates, pseudocoelomates or acoelomates.

·                      Acoelamates- Animals in which the body cavity is absent are known as acoelomates. Example: Platyhelminthes.

·                     Pseudocoelomates- Animals in which the body cavity is not lined by the mesoderm, instead the mesoderm is present in scattered pouches in between the ectoderm and the endoderm is known as the pseudocoelomates. Example: Aschelminthes.

·                     Coelamates- Animals possessing the body cavity which is lined by the mesoderm are known as coelomates. Example: Annelids, Mollusca, Arthropods, Echinoderms, chordates.  

                                       Segmentation 

In some animals, body is segmented externally and internally, with serial repittion of at least some organs. This phenomenon is known as metamerism and the segmented body pattern is known as metameric segmentation. Example: Earthworm.

                                         Notochord

In some animals during embryonic development, a mesodermally derived rod-like structure is formed on the dorsal side, this is known as notochord. Animals with notochord are known as chordates and the animals which do not form notochord are known as non-chordates. Example: Porifera to Echinoderms.  

                                  Animal Kingdom Classification System

There are many different types of animals which are similar and different to each other in many aspects. This is the feature that defines the group. Biologists arrange organisms into groups on the basis of traits which they share with other animals and the genetic relationship with each other. They are organized from most general to most specific category. These categories in the hierarchical system are from higher and most inclusive to lower to more specific are kingdom, phylum, class, order, family, genus and species.
Kingdom is the highest primary division in which all objects are placed.

All animals are part of the Animal Kingdom

Phylum - Each kingdom is divided into smaller units called phyla. Example, chordates are a phylum with members possessing the nerve cord.
Class - The chordates are further divided into classes such as mammalia, birds, Reptilians and Amphibians. Members of each class have a characteristic that they share with the same class but are not found in members of other classes.

Family-Classes are further divided into families. Families contain more than one genus

Genus- Families are sub-divided into genera.

Species-Species is the most fundamental and contains single type of animal.

Animals are classified into two principal groups invertebrates (with-out backbone) and vertebrates (with backbone). Backbone is the observable feature which defines whether the animal is vertebrate or invertebrate.

                                         Invertebrates

Invertebrates are the most abundant organisms on earth. They occupy almost all habitats; they can be found crawling, flying, swimming or floating. Invertebrates are the animals without backbone. These animals do not have internal skeleton made of bone. They play a vital role in the earth's ecosystem. The most common vertebrates include sponges, annelids, echinoderms, molluscs and arthropods. Arthropod includes insects, crustaceans and arachnids. Invertebrates are the animals that do not have a backbone or the vertebral column. Animals without the notochord are invertebrates. Most of the animals are invertebrates. The term invertebrates is a prefixed form of a Latin derived word 'Vertebra'. 'Vertebra' means joint in general, specifically it means 'the joint of the spinal column of the vertebrate'.

                            Invertebrates Classification

Some invertebrate phyla are;

Phylum Porifera

·                     Members of this phylum are commonly known as sponges.

·                     Habitat- They is mostly marine few are found in fresh water. 

·                     Body symmetry- mostly is asymmetrical animals, no definite shape to the body.

·                     Level of organization - These are primitive animals, multicellular with cellular grade of organization. 

·                      Motility- Adult sponges are sessile, that is they need a substratum to attach themselves to a surface and do not move.

·                     Modes of Nutrition- Due to the sessile nature, sponges are filter feeders. 

·                     Digestion- Digestion is intracellular.

·                     Skeleton- The body of sponges is supported by a skeleton made of spicules or spongin fibres. 

·                     Reproduction - Sexes are not separate, they are hermaphrodites. Hermaphroditism - condition where eggs and sperms are produced by the same individual. Sponges reproduce asexually by fragmentation and sexually by formation of gametes.

-Fertilization is internal.

·                     Development- Indirect development, having a larval stage which is morphologically distinct from the adult.

·                     Water canal system- Sponges have water transport system. Water enters through minute pores (ostia) in the body wall into a central cavity known as spongocoel. From the spongocoel water goes out through the osculum. This water system aids in food gathering, respiratory exchange and removal of wastes.

·                     Choanocytes- These are collar cells, they line the spongocoel and the canals. 

·                     Examples: Sycon, Euspongia, Spongilla.

Phylum Cnidaria

·                     Habitat- They are aquatic mostly marine animals, they are sessile or free-swimming. 

·                     Level of organization- They exhibit tissue level of organization.

·                     Body wall- They are diploblastic animals, body wall is made of 2 layers, outer ectoderm and inner endoderm.

·                     Body symmetry- They are radially symmetrical.

·                     Digestive system- They have a central gastro-vascular cavity with a single opening hypostome, which serves as both the mouth and the anus.

·                     Digestion is extracellular and intracellular.

·                     Specialized cells known as the cnidoblasts or cnidocytes which contain the stinging capsules or nematocytes are present on the tentacles and the body. Cnidoblasts are used for anchorage, defense and for the capture of prey.

·                     Some cindarians like corals have skeleton composed of calcium carbonate. 

·                     Cnidarians exhibit two basic body forms called polyp and medusa. The medusa form is umbrella shaped and free-swimming forms like Aurelia or jelly-fish. 

·                     Metagenisis- Cnidarians which exhibit both polyp and medusae form are exhibit alteration of generation, this is known as metagenesis. Poplyps produce medusae asexually and medusae form the polyps sexually. 

·                     Locomotion- The body contains nerve network that allows movement of tentacles and body.

·                     Examples: Aurelia (medusa), Adamsia (polyp).

Phylum Ctenophora:

·                  Ctenophores are commonly known as sea walnuts or comb jellies. 

·                  Habitat- Their is exclusively marine animals.

·                  Body symmetry- They are radially symmetrical.

·                  Body wall- They are diploblastic organisms. 

·                  Level of organization- Ctenophores exhibit tissue level of organization. 

·                  Digestion is both extracellular and intercellular. 

·                   Locomotion-The body bears eight external rows of ciliated comb plates, these help in locomotion. .

·                  Reproduction- Sexes are not separate; reproduction is by sexual means only.

·                  Fertilization-Fertilization is external with indirect development. 

·                  Example: Pleurobrachia

Phylum Platyhelminthes

·                     They are commonly called as flatworms; they have dorso-ventrally flattened body.

·                     Habit- They are mostly endoparasites found in animals and human beings.

·                     Habitat- Fresh water and salt water; terrestrial.

·                     Body symmetry- Flatworms are bilaterally symmetrical. 

·                      Body wall-They are triploblastic animals.

·                      Coelomic cavity-They are acoelomate animals 

·                     Level of organization-Organ level of organization.

·                     Digestive system- In flatworm’s digestive system is incomplete, that is the digestive cavity has a single opening. 

·                     Parasitic flatworms possess hooks and suckers to hold on to the body of the host. Some forms absorb nutrition directly from the host, through their body surface.

·                     Sexes are not separate.

·                     Fertilization is internal and development is indirect, having many larval stages. 

·                     Some members like Planaria possess high regeneration capacity.

·                     Examples: Taenia (tapeworm), Fasciola (liver fluke).

Phylum Aschelminthes

·                     The body of worms of Aschelminthes in cross-section is circular, hence the name round worms. 

·                     Habitat- They may be free-living, aquatic and terrestrial or parasitic in plants and animals.

·                     Levels of organization- Round worms have organ-system level of organization. 

·                      Body symmetry-They are bilaterally symmetrical.

·                      Body wall-They are triploblastic animals.

·                     Coelomic cavity- They are pseudocoelomate animals.

·                     Digestive system- This is the first phylum to have a complete digestive system, with a well developed muscular pharynx. 

·                     Excretory system- An excretory tube removes body wastes from the body cavity through the excretory pore. 

·                     They are dioecious - the sexes are separate i.e., males and females are distinct. Often females are longer than the males.

·                     Fertilization is internal. 

·                     Development may be direct - the young ones resemble the adult, or indirect.

·                     Examples: Ascaris (round worm), Wuchereria

Phylum Annelida

·                     Habitat- They may be aquatic either marine or fresh water; or terrestrial; free-living and sometimes parasitic.

·                     Level of organization- They exhibit organ-system level of body organization and bilateral symmetry.

·                     Body wall- They are triploblastic.

·                     Coelom- They are coelomate animals.

·                     Body is metamerically segmented. The body surface is distinctly marked out into segments of metameres and hence, the phylum name Annelida.

·                     Locomotion- They possesses longitudinal and circular muscles which help in locomotion.

·                     Aquatic annelids posses lateral appendages, parapodia which help in swimming.

·                     Circulatory system is closed.

·                     Osmoregulation and excretion is by Nephridia.

·                     Neural system- It consists of paired ganglia connected by lateral nerves to a double ventral nerve cord.

·                     Nereis is dioecious, but earthworm and leeches are monoecious.

·                     Reproduction is sexual.

·                     Examples: Nereis, Pheretima (earthworm), and Hirudinaria (blood sucking leech)

Phylum Artropoda

·                     It is the largest phylum of the Animalia.

·                     It includes insects, spiders, crayfish, etc.

·                     Level of prganization- They have organ-system level of organization.

·                     Body symmetry- They are bilaterally symmetrical.

·                     Body wall-triploblastic, segmented. Coelomate animals.

·                     The body of arthropods is covered by chitinous exoskeleton.

·                     Body is divided into head, thorax and abdomen.

·                     Jointed appendages - arthros - jointes, poda - appendages, hence the name is derived from this characteristic.

·                     All the arthropods have jointed appendages which give arthropods a wide range of controlled motions.

·                     Respiration is through organs like gills, book gills, book lungs or tracheal system.

·                     Circulatory system- It is of open type. Sensory organs are present, antennae, eyes (compound and simple), statocysts or balance organs are present.

·                     Excretion- It takes place through malphigian tubules.

·                     Mostly they are dioceious. Fertilization is usually internal.

·                     They are oviparous animals.

·                     Examples: Honey bee, Silkworm, Lac insect, Mosquitoes, Locust, Crab

Phylum Mollusca

·                     Habitat- Mollusca are terrestrial or aquatic; they may be marine or fresh water.

·                     Level of organization - They have an organ-system level of organization.

·                     Body symmetry - Bilaterally symmetrical.

·                     Body wall - triploblastic. Coelomate animals.

·                     Body is covered by a calcareous shell.

·                     Body is unsegmented; they have a distinct head, muscular foot and visceral hump.

·                     The radula - Mouth of the molluscs contain tongue-like organ called radula, which has many rows of teeth, which is used to scrape food.

·                     Mantle - It is a fold of skin that surrounds the body organs.

·                     It is a soft and spongy layer of skin that forms a mantle over the visceral hump.

·                     The space between the hump and the mantle is called the mantle cavity.

·                     Feather like gills are present in this cavity.

·                     These gills have respiratory and excretory in functions. Anterior head region has sensory tentacles.

·                     Example: Pila, Octopus, Pearl oyster, Loligo, Sea-hare, Chiton.

Phylum Echinodermata

·                     All the members are marine, live mainly on the ocean floor.

·                     These animals have an endoskeleton of calcareous ossicles, and hence the name echinodermata (spiny bodied).

·                     Level of organization- Organ-system level of organization.

·                     Body symmetry-The adults are radially symmetrical, but the    larvae are bilaterally symmetrical.

·                     Body wall- Triploblastic. Coelomate animals.

·                     Digestive system is complete.

·                     The mouth is present on the ventral side and anus on the dorsal side.

·                     The most distinctive feature is the water vascular system.

·                     This helps in locomotion, capture and transport of food and respiration.

·                     Excretory system is absent.

·                     Sexes are separate.

·                     Reproduction is by sexual means.

·                     Fertilization is usually external.

·                     Development is indirect with free-swimming larva.

·                     Example: Star fish, Sea urchin, Brittle star.

                                          Vertebrates

Vertebrates are the most organized organisms on Earth. They belong to the sub-phylum Vertebrata. They are not the most numerous group of animals; they are the most advanced group of animals. The characteristic that makes vertebrates special are the presence of the spinal cords, vertebrae and notochords.

Most vertebrates have a very well developed nervous system. The vertebrates also have muscles and skeletons which help them move around efficiently and perform complex moves.

                                   Vertebrates Definition

Vertebrate are the animals belonging to the sub-phylum Vertebrata. They belong to the Phylum Chordata. The characteristic of phylum chordata is the presence of notochord, a dorsal hollow nerve cord and paired pharyngeal gill slits. The members of subphylum Vertebrata possess notochord during the embryonic period. The notochord is replaced by a cartilaginous or bony vertebral column in the adult. All vertebrate are chordates but all chordates are not vertebrates. Special characteristics of vertebrates other than the vertebral column are, they have a muscular heart which is two, three or four chambered. For excretion they have kidneys and appendages that are paired which may be fins or limbs.

                             Classes of Vertebrates

Class – Cyclostomata

The living members of this class are all ectoparasites on some fishes. They have a elongated body. They bear 6-15 pairs of gills through which they respire. The mouth of the cyclostomes is sucking circular mouth without jaws. They do not have body scales and paired fins. The vertebral column and the cranium are cartilaginous. Circulation is closed type.

Class – Chondrichthyes

These organisms are marine and have streamlined body. The endoskeleton is cartilaginous. Mouth is located ventrally and the notochord is present throughout life. The gills are separate and are not covered by the operculum. The skin contains minute placoid scales. The placoid scales are modified as teeth and the jaws are powerful. They are predaceous animals. Air bladder is absence in these animals

Class- Osteichthyes

This class includes animals that are both marine and fresh water fishes with bony endoskeleton. Their body is streamlined. Mouth is terminal in position. The gills are covered with operculum on each side and are in four pairs.The skin is covered by ctenoid/cycloid scales. Air bladder is present, it regulates buoyancy. Two-chambered heart is present, with one auricle and one ventricle. They are poikilothermic animals. The sexes are separate, fertilization takes place externally. Most of them are oviparous animals and development is direct, with no larval stages. Examples: Hippocampus, Claries.

Class - Amphibia                               

Ampibians can live both in aquatic and terrestrial habitats. These animals have two pairs of limbs. Body is divisible into head and trunk and tail is present in some animals. The skins of these animals are scaleless and moist. The eyes have eyelids, and the ears are represented by a tympanum. Cloaca is a opening to the exterior, it is a common chamber for the alimentary canal, urinary and reproductive tracts.Gills, lungs and skin aids in respiration. Heart is three-chambered. They are cold-blooded animals. Sexes are separate, fertilization is external. They are oviparous animals and development is indirect.

Class – Reptilia

In Latin repere or reptum means to creep or crawl, hence, the class name refers to locomotion that is of creeping or crawling mode. These animals are mostly terrestrial and their body is covered dry and cornified skin, epidermal scales or scutes. External ear opening is absent, tympanum represents the ear. Limbs, if present are of two pairs. Usually heart is three-chambered, but is four chambered in crocodiles. Sexes are separate, internal fertilization takes place. They are oviparous and development is direct. Examples: Turtle, Chameleon, crocodile.

Class - Aves

Most of the members can fly, except the flightless birds. The characteristic feature of birds is the presence of feathers. The forelimbs are modified as wings. The hind limbs are modified for walking, swimming or clasping and generally have scales. The skin is dry and does not have glands, except a oil gland at the base of the tail. Endoskeleton is bony, and the bones are hollow with air cavities known as pneumatic bones. Heart is four-chambered completely. They are warm-blooded animals. Lungs are the organs of respiration. Sexes are separate, fertilization is internal. They are oviparous animals and development is direct. 

 Examples: Crow, Pigeon, Parrot etc.

Class- Mammalia

Mammals are present in almost all habitats - polar ice caps, deserts, mountains, forests, and grasslands. The unique characteristic of the class mammalia is the presence of milk producing glands (mammary glands), by which the young ones are nourished. The limbs are of two pairs. The skin is covered with hairs. External ear 'pinna' is present. Heart is four-chambered and they are homeothermic animals. Respiration is through lungs. Sexes are separate and fertilization is internal. They viviparous animals, with direct development. 

 Example: Kangaroo, Tiger, Lion, Platypus etc. 

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                                             CONCLUSION

            Biological classification of plants and animals was first proposed by Aristotle on the basic of simple morphological characters.  Linnaeus later classified all living organisms into two kingdoms-plantae and Animalia.  Whittaker proposed an elaborate five kingdom classification-monera, protista, fungi, plantae and Animalia.  The main criteria of the five kingdom classification were cell structure, body organization, mode of nutrition and reproduction and phylogenete relationships

                        In the five kingdom classification, bacteria are included in kingdom monera.  Bacteria are cosmopolitan in distribution.  Kingdom protista include all single-celled eukaryotes such as chrysophyla, dinoflagellates, euglinoids, stem-moulds and protozoan. It have defined nucleus and other membrane found organelles.  The produce sexually and asexually members of kingdom fungi show a great diversity in structure and habitant most fungi are saprophyte in their mode of nutrition.  They show both sexual and asexual reproduction.  The plantae includes all eukaryotic chlorophyll containing organisms.  Algae, bryophytes, pteridophytes, gymnosperms and angiosperms are included in this group. The heterotrophic eukaryotic, multicellular organisms lacking a cell wall are included in the kingdom Animalia. The mode of nutrition of these organisms is holozoic. They reproduce mostly by the sexual mode .Some a cellular organism like viruses and viroids as well as the lichens are not included in the five kingdom classification.