Animal Kingdom

1. Basis for classification

Level of Organization                                

1. Protoplasmic grade – In this grade all life activities are confined within the boundaries of a single cell which is a structural and functional unit of life, e.g., Protozoa and other unicellular organisms.

2. Cellular grade – It is a loose association or aggregation of cells that are functionally differentiated, e.g., sponges.

3. Tissue grade – An aggregation of cells which act in co-ordination, e.g., Cnidarians.

4. Tissue-organ grade – When tissues aggregate to form a particular organ. First appeared in platyhelminthes.

5. Organ-system grade – When organs work together to perform same function such as digestion, respiration, circulation etc, e.g., Most of the animals.

Body Plan
i) Cell Aggregate Body plan – The body is multicellular and each cell acts almost independently e.g., Porifera (Sponges)
ii) Blind Sac – The body resembles a sac and contains a single cavity with one opening that serves for ingestion and egestion both, e.g., Cnidaria (Hydra), Platyhelminthes (Flatworms)
iii) Tube within a tube – The body is made up of two tubes, outer body wall and the inner digestive tract, e.g., Annelida.


1. Spherical symmetry – Found in spherical body. All planes that pass through the center will cut it into similar halves. E.g., Protozans like Volvox, Heliozoa, Radiolaria.

2. Radial symmetry – The body is in the form of a flat or tall cylinder. All the lines passing through longitudinal axes in a radiating manner divide the body into equal halves, e.g., Hydra.
a) Biradial symmetry – Divides the animal into two equal halves, e.g., Ctenophora and most of the anthozoans (e.g. Sea anemones)
b) Pentamerous radial – Divides the animal into 5 equal parts, e.g., Star fish.

3. Bilateral symmetry – The body is divided into two equal halves by a single median, longitudinal or sagittal plane. E.g., most higher animals.

4. Asymmetry – When an animal cannot be divided into equal parts by any plane, e.g., Amoeba, most sponges.

Germ Layers
During early stages of embryonic development the cells are arranged in groups forming germ layers. They appear in gastrula stage.

1. Diploblastic animals – Having two distinct germ layers, i.e., outermost ectoderm and inner most endoderm, e.g., Cnidarians.

2. Triploblastic animals – Having three distinct germ layers, i.e., ectoderm, mesoderm and endoderm. The mesodermal layer always lies between ectoderm and endoderm, e.g., most metazoans (Bilateria).

Body Cavity or Coelom
During early stages of embryonic development the cells are arranged in groups forming germs layers (ectoderm, mesoderm and endoderm). Depending upon their distribution animals may be diploblastic or triploblastic.
The space between body wall and alimentary canal remains lined by mesoderm and is called coelom. On the basis of development coelom is one of the following types.

1. Acoelomates – The animals without coelom or body cavity are called acoelomates, e.g., Cnidarians, flatworms (platyhelminthes).

2. Pseudocoelom – The body cavity between the gut and body wall is not lined by mesoderm (peritoneum), e.g., Nemathelminthes (Ascaris).

3. Eucoelom – The body cavity lined from all sides by mesodermal peritoneum.
a) Schizocoel – formed by the splitting of mesodermal band, e.g., Annelids, Arthropods, Molluscs.
b) Enterocoel – formed from the pouches of the archenteron or primitive gut, e.g., Echinoderms and chordates.

Segmentation or metamerism is a serial repetition of similar body segments along the longitudinal axis of the body. Metamerism permits greater body mobility and complexity of structure and function.
Metamerism is found in phyla annelida, arthropoda in addition to chordata.

  • Annelida – both internal and external segmentation
  • Arthropoda – only external segmentation
  • Chordata – only internal segmentation

The coelomate phylum can be divided into two distinct evolutionary lines, depending upon the fate of blastopore and the pattern of cleavage.
Blastopore – During animal development, in gastrulation, the rudimentary gut of the embryo forms a blind pouch (Archenterons) , which has a single opening to the outside known as blastopore. A second opening is formed later at the opposite end of the archenteron to produce a digestive tube with a mouth and an anus.

Mouth develops from the first opening, the blastopore. Mouth develop from second opening and the blastopore usually forms the anus, not the mouth.
Spiral cleavage takes place during early embryonic development in which planes of cell division are diagonal to the vertical axis of embryo. Zygote undergoes radial cleavage in which cleavage planes are either parallel or perpendicular to the vertical axis of the egg.
Determinate cleavage, forms mosaic embryo. Indeterminate cleavage, forms regulative embryo.

The concentration of nervous tissue and sense organs in head is known as cephalization. It is found in bilaterally symmetrical animals. It is most efficient positioning of all organs for sensing the environment and responding to it. The process of cephalization starts from the phylum platyhelminthes.


S.No. Chordates Non-chordates
1. Notochord present. Notochord absent.
2. Central nervous system is dorsal,
hollow and single.
Central nervous system is ventral, solid
and double.
3. Pharynx perforated by gill slits. Gill slits are absent.
4. Heart is ventral. Heart is dorsal (If present).
5. A Post-anal part (tail) Is present. Post-anal tail is absent.

The animal kingdom includes about 35 phyla out of which 11 are considered as major phyla.

About 99 percent of animals are invertebrates (animals without backbone) and the remaining represents the vertebrates.

2. Tree of animal classification

Comparative Study of Phyla

  Habitat Nutrition Respiration Circulation
Porifera All marine except spongilla (fresh water) Intracellular (in choanocytes, and amoebocytes) Through general body surface. Water canal system.



Cnidaria Mostly Marine First extracellular (First in gastovascular cavity) and then intracellular (Nutritive muscle  cell) Through general body surface. Gastrovascular circulation.
Ctenophora Exclusively Marine First extracellular (First in gastovascular cavity) and then intracellular (Nutritive muscle  cell) Through general body surface. Gastrovascular circulation.
Platyhelminthes Mostly endoparasite Through general body surface. Parenchymal circulation
Aschelminthes May be free living aquatic, and Terrestrial Complete digestive canal with mouth specialized into muscular pharynx, straight non muscular intestine, and posterior anus. Digestion is extracellular Through general body surface. Pseudocoelomic circulation
Annelida May be aquatic (Marine and fresh water) or terrestrial. By moist skin, or gills, or parapodia.


Blood vascular system (open and close type)
Arthropoda All the habitat By General body surface, gills, trachea or book lungs. BVS (both open and closed type)


Mollusca Terrestrial or aquatic, marine or fresh water Respiration direct or by feather like gills or lungs or both. Haemocoelomic circulation (open type)


Echinodermata Exclusively Marine Includes dermal branchiate, tube feet, respiratory tree and bursae. Water vascular system- haemal system (closed type)
  Excretion Movement and Locomotion Nervous Reproductions
Porifera Specialised organs absent, takes place through body surface The body is supported by skeleton made up of spicules or spongin fibres.    Mostly sessile. No nerve cells Both asexual (by internal budding or gemmule formation) and sexual reproduction – (internal fertilization) indirect development (parenchymula, amphiblastula larvae)
Cnidaria Specialised organs absent, takes place through body surface Both sessile and freely movable. Muscular system includes    longitudinal and circular muscle fibers. Nerve cell appears first time. Both sexual and asexual reproduction
  Excretion Movement and Locomotion Nervous Reproductions
Ctenophora Specialised organs absent, takes place through body surface Both sessile and freely movable. Muscular system includes    longitudinal and circular muscle fibers.


brain absent but a diffuse network of neurons present Only sexual reproduction (bisexual or hermaphrodite). External fertilization and indirect development (cydipid larvae).
Platyhelminthes Through flame cells Presence of both longitudinal and circular muscle fibre. Nerves tissue developed and it is primitive type. These are mostly bisexual, fertilization is internal.
Aschelminthes ‘H’ shaped canal, Ranette cells Mostly longitudinal fibres.


Circumpharyageal nerve ring and a solid double ventral nerve cord. Unisexual or dioecious, with distinct sexual dimorphism. Male is smaller in size, has penial spicules and cloacal aperture. (Anus is female).
Annelida Nephridia, chloragogen cells, Botryoidal tissue (in Leeches).


Muscle (both longitudinal and circular). Parapodia, setae, coelomic fluid act like hydrostatic skeleton. Circum-esophageal nerve ring and double ventral nerve cord Sexes may be unisexual (Nereis) or bisexual (e.g., earthworm, leech) Generally cross fertilization which may be  external (Nereis) or internal (leech) Development is direct (earthworm, leech)or indirect (Nereis) and includes free swimming trochophore larvae.
Arthropoda Malphigian tubule, green gland, coxal gland. Jointed legs Formed of few pairs of ganglia joined by nerve connective and commissures. They are mostly dioecious. Fertilization is usually internal.
Mollusca Mollusca – Feather Like gills, Metanephridia.


Muscular foot


Formed of two nerve rings and radial nerve cords. Sexes are generally unisexual fertilization may be external or internal.

Development generally indirect (glochidium, trochophore, or veliger larvae) or direct (cephalopods molluscs).

Echinodermata Specialized excretory organ absent Tube feet, water vascular system. Poorly developed, brain is absent Always unisexual, without sexual dimorphism. External fertilization and always indirect development (Dipleura, bipinaria, larvae).


3.  Protozoa

General Characteristics

  • Protozoans are small, generally microscopic organisms where single cell performs all the vital activities, hence also called as acellular organisms.
  • Generally uninucleate but all ciliates and many amoeboid forms are multinucleate. Nucleus is vesicular and massive.
  • Locomotory organs are pseudopodia in Sarcodina, flagella in Mastigophora, cilia in Ciliata and absent in Sporozoa (parasitic forms).
  • Nutrition may be holophytic (plant – like), holozoic (animal-like), saprozoic or parasitic.
  • Contractile vacuole is found in almost all freshwater protozoans for maintenance of osmotic balance of cell body and excretion.
  • Reproduction is asexual or sexual. Most flagellates, rhizopods and ciliates show asexual reproduction by binary or multiple fission, budding or sporulation. Some ciliates, e.g., Paramecium reproduces by sexual mode, i.e. conjugation. In sporozoa, some stages of life cycle show formation of morphologically distinct gametes.
  • Cyst formation during unfavourable conditions commonly occurs among the freshwater and parasitic protozoans.
  • Life cycle often exhibits alternation of generation, i.e., – includes both asexual and sexual phase.
  • Protozoans show mainly two modes of life,
    i) Free living, inhabiting fresh or salt water and damp places,
    ii) Parasitic, living as ectoparasites or endoparasites on other animals and plants.

Classification of Protozoa

Class Mastigophora Rhizopoda or Sarcodina Sporozoa Ciliata
  • One to many flagella acts as locomotory and food capturing organs
  • Reproduction asexual by longitudinal binary fission
  • Body naked without definite pellicile or provided with shells.
  • Pseudopodia are locomotory and food-capturing organs.
  • Asexual reproduction by binary or multiple fission.


  • Adult sporozoans do not possess external organs of locomotion
  • Reproduction both sexual and asexual
  • Exclusively parasitic forms
  • Body has firm pellicle.
  • Locomotory and food capturing organs are cilia.
  • Usually two kinds of nuclei : larger macronucleus (for metabolic activities) and smaller micronucleus (for sexual reproductions).
  • Asexual reproduction by binary fission and sexual reproduction by conjugation.
Example Euglena, Noctiluca, Trypanosoma (causes sleeping sickness) Leishmania donovani (causes kala azar), Giardia (causes dysentery). Amoeba, Entamoeba (causes dysentery), Polystomella, Arcella. Plasmodium (causes malaria), Monocystis (Parastie in seminal vesicles of earthworm). Eimeria, Sarcocystis Paramecium, Opalina, Nycotherus. Vorticella.


  • Discovered in RBCs of man by Charles Laveran while Ronald Ross observed oocysts of Plasmodium in the stomach wall of female Anopheles mosquito.
  • Out of about 60 species only four species cause malaria in man.
Species Diseases
1. Plasmodium vivax Benign tertian malaria
2. P. malariae Quartan fever
3. P. falciparum (most dangerous) Malignant fever, Cerebral malaria, Estivo-autumnal fever, Black water fever
4. P. ovale Mild tertian fever.
  • Plasmodium is a digenetic, intracellular parasite found in the blood of man.
  • Asexual cycle occurs in man by a process called Schizogony (in liver and RBCs).
  • Sexual cycle is completed in mosquito by gametogony and sporogony.
  • Infective stage of Plasmodiumsporozoite.


•  Monogenetic, endoparasite found in the mucosal and submucosal layers of the large intestine of man.

•  Found in two forms
i) Trophozoite  or Magna form – Pathogenic
ii) Pre-cystic  or Minuta form – Non-pathogenic.

•  E.gingivalis: Non-pathogenic parasite found in tartar of teeth, aggravates pyorrhea (doesn’t cause pyorrhea)

•  Giardia (Grand old man of intestine): Resides in the upper part of small intestine of man, causing abdominal discomfort and diarrhea.

•  Trichomonas:
a) buccalis: found in bucal cavity of human, causes pyorrhea.
b) vaginalis:  found in vagina of women, causes leucorrhoea.
c) hominis:  found in colon of man causes diarrhoea.

•  Trypanosoma: Is digenetic endoparasite found in the blood of vertebrates finally invading CSF  causing African sleeping sickness. Its secondary host is Tse-tse fly (Glossina palpalis)
a) gambiense:  causes African sleeping sickness of Gambian fever.
b) rhodesiense : causes Rhodesian fever confined to east and central parts of Africa.
c) cruzi: causes chagas disease in children in South America.
d) brucei :  causes ‘Nagana’ disease in horses, donkeys, camels and cattles.
e) evansi :  ‘surra’ disease in horses, camels, cattles and dogs.

L. donovani, a digenetic endoparasite found in reticulo-endothelial system of spleen, liver, WBC and bone marrow and causes kala-azar or visceral leishmaniasia.

Secondary host :  sand fly (Phlebotomus argentipes)
(a)  L. tropica :  causes oriental sore  or cutaneous leishmaniasis or Delhi boils in man.
(b)  L. brassiliensis :  causes ‘Espundia’ or naso-oral leishmaniasis  in South America.


  • Primitive multicellular animals with cell aggregate body plan, acoelomate, diploblastic, having radial or bilateral symmetry while mostly are asymmetrical.
  • Fresh water or marine, sessile (adult forms) solitary or colonial. Body porous supported by a skeleton of spicules of spongin fibres and a canal system lined with flagellate collar cells or choanocytes.
  • Appendages absent; no proper cephalization; nervous system absent.
  • Canal system consists of numerous pores called ostia leading into central cavity called spongocoel or paragastric cavity which open to the outside by a large pore called osculum.
  • Digestion intracellular, amoebocytes aid in distribution of food.
  • Reproduction through fragmentation, gemmules and sexual reproduction. Development involves a motile larva called amphiblastula and parenchymula.
  • Water canal system
  • Pathway of water circulation
    Water –> Ostia –> Spongocoel (water circulates with flagellated choanocyte or collar cells) –> osculam  –> exit
  • This pathway of water transport is helpful in food gathering, respiratory exchange and removal of waste.
    Examples: Sycon (Scypha), Spongilla (Fresh water sponge) and Euspongia (Bath sponge).

    Examples for Porifera : (a) Sycon (b) Euspongia(c) Spongilla

1.  Classification (based on skeleton)

Class Calcarea Hexactinellida Demospongiae
Character Calcareous spicules Six-rayed silicious spicules Spongin Fibre or Spongin fibre with silicious spicules, or both absent
Example Leucosolenia, Sycon Euplectella, Hyalonema Euspongia (only spongin)
Spongilla, Chalina (both spicules and spongin)
Common Names
Scypha Urn sponge (Crown sponge)
Euplectella Venu’s flower basket
Pheronema Bowl sponge
Hyalonema Glass-rope sponge
Cliona Boring sponge (Sulphur sponge) Harmful to Pearl industry.
Chalina Mermaids gloves (Dead man’s finger)
Spongilla Fresh water sponge
Euspongia Bath sponge
Poterion Neptunes goblet
Hippospongia Horse sponge
Hircinia Horny sponge

5.  Coelenterata

  • Diploblastic metazoa having tissue grade of body organization blind-sac body plan, may be solitary or colonial. Aquatic-mostly marine except few fresh water forms eg., Hydra.
  • Radially or biradially symmetrical with a central gastovascular cavity communicating with the exterior by the mouth. Anus absent.
  • Short and slender tentacles encircle the mouth in one or more whorls, serving for food capture, ingestion and for defence.
  • Exhibit Polymorphism with 2 forms polyp (sessile and asexual zooid) and medusae (free-swimming and sexual zooid).
  • Nervous system primitive and consists of one or more networks of nerve cells or neuritis located in the ectoderm and endoderm. Sense organs consists of statocysts (tentaculocysts), ocelli and olfactory pits.
  • Digestion – Both extra and intracellular.
  • Respiration and excretion occurs through general body surface.
  • Possess nematocysts serving the function of paralyzing the prey by injecting poison or to hold the prey or used for adhesion.
  • Reproduction both asexual (by budding) or sexual (by sperm and ova). Eggs develop into a ciliated larva known as planula (Obelia) or ephyra (Aurelia).
  • Life history exhibits the phenomenon of alternation of generation or metagenesis
  • Presence of cnidoblasts or cnidocytes (contain the stinging capsule or nematocysts).
  • Present on the tentacles and the body wall. Cnidoblasts are used for anchorage, defence and for the capture of prey.

Examples of Coelenterata indicating outline of their body form: (a) Aurelia (Medusa) (b) Adamsia (Polyp)

Asexual reproduction by budding (polyps) and sexual reproduction by medusae. Development is generally indirect (except hydra) and include planula larva for dispersal. It shows alternation of generation (metagenesis) in which polyps produce medusa by vegetative budding and medusae form the polyps by sexual reproduction.

  • Polyp – mouth and tentacles upwards.
  • Medusae – Mouth and Tentacles  downwards.

Examples: Physalia (Portugese man-of-war) Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan) Meandrina (Brain coral)

2.  Classification based on dominance of Medusae or polyp form in the lifecycle.

Class Hydrozoa Scyphozoa Anthozoa (all marine)
Character Either polyp only or polyp and medusae both.
Show metagenesis.
Represented by medusae Represented by polyp form
Largest class
Example Hydra, Obelia, Physalia,
Aurelia Gorgonia, Adamsia, Astraea, All
marire corals.
Common Names
Obelia Sea fur
Millipora Stinging coral
Physalia Portuguese man-of-war
Velella Little sail
Chiropsalmus Sea wasp
Aurelia Jelly fish
Metridium Sea anemone
Adamsia Sea anemone
Pennatula Sea pen
Corallium Precious red coral
Meandrina Brain coral
Tubipora Organ pipe coral
Heliopora Blue coral
Astraea Stony coral
Virgularia Walking stick
Fungia Mushroom coral
Alcyonium Dead man’s finger

6.  Ctenophora

  • Exclusively marine, commonly known as sea walnut or comb Jellies (body bears eight   external rows of ciliated comb plates, which help in locomotion). Exhibit property of Bioluminescence.
  • Ctenophores are colourful, jelly-fish-like (similar to medusa form of Cnidarians)

  • Nematocysts absent, but tentacles (generally one pair) bear adhesive cells called Colloblast or Lasso cells for capturing the prey.
  • Body unsegmented, body wall probably triploblastic. Epidermis is ciliated and the mesenchyma/mesoglea contains muscle fibres, connective tissue and amoeboid cells.
  • Polymorphism absent.
  • Statocyst, a balancing organ, present.
  • Asexual reproduction absent, but great power of regeneration present.
  • All bisexual (hermaphrodite), gonads endodermal in origin. Fertilization external or internal.
  • Some ctenophores show ‘Dissogeny’, in which both larvae and adults become sexually mature. Paedogenesis is common.
    Examples: Pleurobrachia and Ctenoplana.

7.  Platyhelminthes
Dorso – ventrally flattened body (flatworms).

  • The flat worms are mostly parasites but some are free living e.g., Planaria
  • Acoelomate, triploblastic, bilaterally symmetrical and dorsiventrally flattened animals with organ system level of organisation.
(a) Tape worm (b) Liver fluke
  • Body segmented (false segmentation) in class cestoda.
  • Body covered with a cellular, syncytial one layered partly ciliated epidermis; while in parasitic trematodes and cestodes epidermis is lacking and the body is covered with cuticle.
  • Exoskeleton and Endoskeleton are completely absent. However hooks, spines, suckers, may be present which act as adhesive organs.
  • The space between the body wall, alimentary canal and other organs if filled with a peculiar connective tissue, called the parenchyma. It helps in transportation of food materials.
  • Digestive system is totally absent in tapeworms but in other flatworms (Trematoda and Turbellaria) it consists of mouth, pharynx and blind intestine (anus absent).
  • Excretory system consists of single or paired protonephridia with flame cells.
  • Nervous system is primitive. The main nervous system consists of a pair of cerebral ganglia or brain and one to three pairs of longitudinal nerve cords connected to each other by transverse commisures. This type of nervous system is called ladder type of nervous system.
  • Sense organs are of common occurrence in Turbellaria but these are greatly reduced in parasitic forms.
  • Sexes are united, i.e., hermaphrodite with very few exceptions.
  • Asexual reproduction by fission occurs in many fresh water Turbellarians
  • In majority of forms, eggs are devoid of yolk but provided with special yolk cells and are covered by egg shell.
  • Cross fertilization in trematodes and self-fertilization in cestodes is very common. Fertilization is internal development incomplete.
  • Life cycle complicated, involves one or more hosts.
  • Mostly endoparasites. Presence of hooks and suckers in the parasitic form. Planarians possess high regeneration capacity.
    Examples: Taenia (Tapeworm), Fasciola (Liver fluke)

Classification – based on mode of life

Class Turbellaria Trematoda (Fluke) Cestoda (Tapeworm)
Character Mostly free living Ecto or Endoporasitic worms Ecto or Endo parasites of  Vertebrates.
Example Planaria (Dugesia) Fasciola (Liver Fluke) Schistosoma (Blood)-Fluke Taenia solium (Pork tapeworm) Taenia saginata (Beef tapeworm)

8.  Aschelminthes
Circular is cross section (Roundworms).

  • May be free-living, aquatic and terrestrial or parasitic  in plants and animals.
  • Bilaterally symmetrical, triploblastic, unsegmented, cylindrical worms.
  • Organ-system level of organization.
  • No appendages in roundworms.

Aschelminthes– Roundworm

  • The body wall consists of firm, non-living, resistant cuticle, epidermis and muscle layer. The cuticle is moulted (changed) four times during growth period. The epidermis is syncytial, but lacks cilia. The musculature contains longitudinal fibres only.
  • There is no mineralized skeleton. High fluid pressure in the pseudocoelom maintains body shape. It is called hydroskeleton.
  • There is a straight, one way digestive tract with mouth as well as anus. Such a digestive tract is said to be complete. Mouth is bordered with 3-6 lips having sensory papillae. Pharynx is muscular with 3-rayed cavity. It is used to suck the food. Intestine is non muscular.
  • Respiration occurs by diffusion through the body surface.
  • Nervous system consists of circum pharyngeal nerve ring and six longitudinal nerve cords.
  • Excretory system consists of gland cells or canals or both. Some forms have protonephridia.
  • They exhibit sexual dimorphism; males being smaller than females. Fertilization is internal. Development direct. There is no asexual reproduction.
  • Cleavage is determinate and spiral.
    Example Ascaris (Roundworm)
    Ancylostoma (Hookworm) Wuchereria (Filarial worm)

Life cycle of Ascaris

Male Ascaris Female Ascaris
1. It is smaller with curved posterior end. It is longer than male with straight posterior end.
2. Two equal chitinous spicules or penial setae project through cloacal apertures Spicules are absent
3. Anus and genital aperture open into common chamber, the cloaca There are separate anus and genital aperture (1/3rd from anterior end); cloaca absent.

9.  Annelida

  • The organisms are triploblastic, bilaterally symmetrical coelomate, organ system level of body organization and metamerically segmented.

(a) Nereis  (b) Hirudinaria

  • These are the first animals to have generally closed circulatory system. Colour of blood is red due to the presence of hemoglobin dissolved in blood plasma.
  • Body wall with an epidermis of columnar epithelium, coated externally by moist albuminous cuticle and with circular and longitudinal muscle fibres
  • Chitinous setae, aiding in locomotion, may or may not be on fleshy parapodia; absent in leech.
  • A true coelom is present. Annelids are first animals to have a true schizocoelic coelom. Coelom is divided by septa into compartments.
  • The coelomic fluid acts as a hydrostatic skeleton.
  • Digestive system is complete and digestion is extracellular.
  • Respiration by moist skin (cutaneous respiration) or through gills (branchial respiration).
  • Blood vascular system is usually closed. Respiratory pigments either haemoglobin or erythrocruorin dissolved in blood plasma. Free amoeboid blood corpuscles are present, but there are no RBC’s. In leech, there is no true blood vascular system.
  • Nephridia is the excretory organ. Ammonia is chief excretory waste.
  • The nervous system consists of a nerve ring and a solid, double, mid-ventral nerve cord with ganglia and lateral nerves in each segment.
  • Sensory organs include tactile organs, taste buds, statocysts, photoreceptor cells and eyes with lenses.
  • The sexes may be separate (e.g., Nereis) or united (e.g., earthworm, leech).
  • Development is mostly direct (e.g., earthworm). There is indirect development in Nereis. Larva, when present is trochophore.

Examples : Nereis, Pheretima (Earthworm) and Hirudinaria (Blood sucking leech).

4.  Classification based on number and presence or absence of setae and parapodia

Class Polychaeta Oligochaeta Hirudinea
Character Parapodia and Numerous setae Few setae no parapodia Without parapoidia and setae and ectoparasite
Example Nereis Pheretima, Lumbricus magascolex Hirudinaria, Pontobdella

Aphrodite (sea mouse), Serpula (Fan worm)

10.  Arthropoda

  •  Largest phylum, includes 900,000 species
  • Triploblastic, bilaterally symmetrical, metamerically segmented animals.
  • Body is covered with a thick, tough and non-living chitinous cuticle as exoskeleton.
  • Body segments usually bear paired lateral and jointed appendages.
  • Body divisible into head, thorax and abdomen; head and thorax often fused to form cephalothorax.
  • The true coelom is reduced in adults; is only represented by the cavities of the reproductive and excretory organs. The body cavity is a haemoceol.
  • Developed sensory organs, with compound eyes and statocyst (Balancing organs).
  • Digestive system is complete; mouth parts adapted for different modes of feeding. The alimentary canal consists of stomodaeum (foregut), mesenteron (mid gut) and proctodaeum (hind gut).
  • The respiratory organs are gills or book gills in aquatic forms and trachea or book lungs in terrestrial forms.
  • Circulatory system open with a dorsal heart, arteries and blood sinuses.
  • Excretory organs are green glands or malpighian tubules. In some forms, coxal glands are excretory organs.
  • Nervous system with a dorsal nerve ring and double ventral solid nerve cord.
  • Sensory organs comprise simple eyes, compound eyes, chemoreceptors and tactile receptors. Some forms also have statocysts.
  • Endocrine glands are present. Insects secrete pheromones which are used for communication between two organisms of the same species.
  • Sexual dimorphism is exhibited. Fertilization is internal; oviparous or ovo-viviparous; development direct or indirect. Parthenogenesis occurs in some forms.

    (a) Locust (b) Butterfly (c) Scorpion (d) Prawn

Examples: Economically important insects –Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect) Vectors – Anopheles, Culex and Aedes (Mosquitoes) Gregarious pest – Locusta (Locust) Living fossil – Limulus (King crab).


Based on body division and presence or absence of  certain appendages.

Class Crustacea Arachnida Chilopada Diplopoda Insecta (Hexapoda) largest class Onychophora
  •  C + A,  two pairs of antennae
  •  Cephalothorax covered by carpace
  • C + A
  • six pairs of appendages
  • No Antennae
  • Head and Trunk each trunk segment with a pair of legs
  • Poison Claw
  • H + T + A
  • Thoracic segment with 1 pair of legs and abdominal with 2 pairs of legs
  • H + T + A
  • a pair of Antennae
  • The thorax consist of three segments, with three pair of legs and usually two pairs of wings
§ Segmented worm like

§ Unjointed legs

Example Palemon (prawn) cancer (crab) scorpion, spider, tick, mite Scolopendras (centipede) Julus (millipada) cockroach, beetle, wasp, butterflies, Peripatus (walking worms)

H – head, A – Abdomen, T – (Thorax), C – (Cephalothorax)

11.  Mollusca

Second largest animal phylum. They are terrestrial or aquatic, ( both marine and free water )

Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Seahare), Dentalium (Tusk shell) and Chaetopleura (Chiton).

  • The body is soft, unsegmented (except in monoplacophora), triploblastic and bilaterally symmetrical (in some mollusks like Pila, due to torsion during growth, the adults become asymmetrical).
  • Body is covered by a calcareous shell, unsegemented with a distinct head, muscular feet and visceral hump. A soft and spongy layer of skin forms a mantle or pallium present over the visceral hump.
  • Presence of Radula (Rasping organ) and hepatopancreas as digestive gland.
  • Body is commonly protected by an exoskeletal calcareous shell of one or more pieces, secreted by mantle. Shell may be external (e.g., most of mollusks), internal (e.g., slug, cuttle fish, squid) or absent (e.g., Octopus).
  • Head is distinct, bearing the mouth and provided with eyes, tentacles and other sense organs except the pelecypoda and scaphopoda.
  • Mantle or Pallium is a thin, fleshy fold on the dorsal side. It is enclosed in a space, between itself and the body which is called mantle or pallial cavity.
  • The body is lined with single-layered epidermis which is usually ciliated. Muscles are unstriped and occur in bundles.
  • Ventral body wall is modified into a muscular, flat or plough like surface, the foot which is variously modified for creeping burrowing and swimming.
  • Body cavity is haemocoel. The true coelom is generally limited to the pericardial cavity (space around the heart), and a small spaces within kidneys and gonads.
  • Digestive tract is complete. Buccal cavity often contains a rasping organ, the radula, with transverse rows of test (except in Pelecypoda). In gastropods, scaphopods and cephalopods the intestine become U-shaped bringing the anus to an anterior position.
  • Respiration usually takes place by gills, called the ctenidia, located in the mantle cavity, but may occur by body surface, mantle or lung (pulmonary sac).
  • The circulatory system is open. It includes dorsal pulsatile heart and few arteries that open into sinuses. Blood consists of copper containing pigment known as haemocyanin.
  • Excretion by paired metanephridia (kidneys). Gills are also excretory in function. The excretory matter is ammonia or uric acid.
  •  Nervous system consists of paired cerebral, pleural, pedal and visceral ganglia joined  by longitudinal and transverse connectives.
  • Sense organs include eyes (photoreceptors) and tentacles (tactoreceptors) on the head. Statocysts for equilibrium osphradia for testing chemical and physical nature of water (chemoreceptor).
  • There are three types of larva-trochophore, veliger (gastropoda) and glochidium (pelecypoda).

Phylum mollusca is divided into six classes on the basis of foot and shell

Class Monoplacophora Polyplacophora (Amphineura) Gastropoda Bivlalvia pelycopoda Scaphopoda Cephalopoda
Character · One shell
· Segmented mollusc
Shell is formed of 8 plates. · Spirally coiled shell.
· Largest class.
· Property of torsion
· Shell with 2 valves Tubular shell · Shell many be internal (Sepia) or external (Nautilus) or absent (Octopus)
Example Neoplina
Connecting link between Annelida an Mollusca.
Chiton Pila (apple snail)
Limax (Slug)
Aplysia (Sea hare)
Unio (Fresh water mussel) pinctada (pearl oyster) Teredo (Shipworms) Dentalium (Elephant Tusk) Sepia (cuttlefish)
Loligo (Squid)
Octopus (Devilfish)

12.  Echinodermata (spiny bodied animals)

  • Exclusively marine, presence of endoskeleton made up of calcareous ossicles. Adults are radially symmetrical but larvae are bilaterally symmetrical.
  • Triploblastic, enterocoelous coelomates with pentamerous radial symmetry having a calcareous endoskeleton of separate plates embedded in the skin.
  • Presence of pedicellariae (capture and removal of debris).

  • Body unsegmented with globular, star-like, spherical, discoidal or elongated shape. Body surface is marked by five symmetrically radiating areas (ambulacra) and five alternating inter-radii (inter-ambulacra).
  • Many echinoderms bear spines and pincer like pedicellariae. The spines are protective in function. The pedicellariae keep the body surface clear of debris and minute organisms.
  •  Body wall consists of an outer epidermis (single layered and ciliated), a middle dermis and an inner lining of peritoneum.
  • Alimentary canal straight or coiled. Presence of Aristotle’s lantern as masticatory apparatus in sea urchin.
  • Respiratory organs include dermal branchiae (eg. star fish), tubefeet, respiratory tree (e.g., Holothuria), bursae (e.g., brittle star) and peristomial gills system.
  • Presence of ambulacral system or water vascular system is the most characteristic feature. A perforated plate called madreporite, allows water into the system. Water vascular system is of coelomic origin.
  • Tube feet help in locomotion.
  • The circulatory system is greatly reduced and is of open type. It is called haemal system. Blood often lacks a respiratory pigment. There is no heart.
  • Excretory system is wanting. Nitrogenous waste diffuses out via gills.
  • The nervous system includes a nerve ring and radial nerve cords. There is no brain.
  • Poorly developed sense organs include tactile organs, chemoreceptors, terminal tentacles, photoreceptors and statocysts.
  • Reproduction both asexual and sexual. Sexes are usually separate with few exceptions. Copulation does not occur. Fertilization is external.
  • Development indirect through free-swimming larva forms. The bilaterally symmetrical larva undergoes metamorphosis to change into the radically symmetrical adult.
  • Echinoderms resemble chordates in early embryonic development.

Classification based on body shape, position and kind of larvae form –

Class Asteroidea Ophiuroidea Echinoidea Holothuroidea Crinoidea
Character · Star shaped body

· Bipinnaria larvae

· Star shaped pluteus larvae Globular body.

Echinopluteus larvae

· Cucumber like body

· Auricularia larvae

· Flower like body

· Doliolaria larvae.

Example Asterias (starfish) Ophiothrix (Brittle star) Echinus (seaurhin) Cucumaria (sea cucumber) Antedon (feather star or Sea Lily)

13. Hemichordata

  • A small group of worm like marine animals
  • Cylindrical body composed of anterior proboscis, a collar and a long trunk.
  • Open circulatory system.
  • Respiration through gills.
  • Proboscis gland as an excretory organ.
  • Sexes are separate.
  • External Fertilization and indirect development.
    Example –Balanoglossus and Saccoglossus

14.  Chordata

  • Presence of notochord.
  • A dorsal hollow nerve cord.
  • Paired pharyngeal gill slits.
  • Presence of post anal tail.

  • Presence of endostyle or thyroid gland.
  • Mostly closed circulatory system.
  • Cyclostomes, pisces, amphibians and reptiles are poikilotherms (cold blooded) while Aves and Mammals are homeotherms (warm blooded).
Protochordata or acraniata (only marine) Vertebrata or Craniata both aquatic (marine and freshwater) and Terrestrial
  • Urochoradata or Tunicata or Ascidian
  • Notochord present only in larval tail.

  • Cephalochordata Notochord extends from head to tail region and  persistent throughout their life
  • They are most typical chordates, which possess all chordate characteristic.
  • It possess notochord during embryonic condition and it is replaced by a cartilagenous or bony vertebral column.
  • Presence of ventral muscular heart with two, three or four chamber heart.
  • Kidney for excretion and osmoregulation. Presence of paired appendages which may be fins or limbs.



Agnatha (lacks Jaw) –> Class cyclostomes Gnathostomata (bear Jaw)
  • Ectoparasite in some fishes.
  • Circular mouth bounded by suctorial funnel but it is jawless.
  • 6-15 pairs of gill slits for respiration.
  • Scaleless skin with median unpaired fins.
  • Cartilagenous cranium  and vertebral column.
  • Closed circulatory system with 2-chambered heart
AdultSEA WATERcatadromousanedromousTo fresh water for spawning                                                                                                                   larvae (Ammocoete)                                               Adults dies after spawning
Pisces Tetrapoda
  • Presence of fins and dermal  scales.
  • 2-chambered heart.


  •  Two pairs of pentadactyl limbs.
  • Exoskeleton of epidermal hair, feathers and scales.
  •  3 or 4 chambered heart.

A jawless vertebrate – Petromyzon

Super class → Pisces

  • Locomotion by fins.
  • Branchial respiration (by gills).
  • Presence of dermal scales.
  • Presence of lateral line system as sensory organ.

15.  Pisces

Class Chondrichthyes-(cartilaginous fish) Class Osteichthyes – (Bonyfish)
  • Always marine
  • Placoid scale
  • Presence of cloaca
  • Presence of 5-7 pairs of gills slits without operculum (gill covering).
  • Without swimbladder, hence they have to swim continuously
  • Presence of claspers as copulatory organ
  • Usually internal fertilization
  • Female is generally oviparous but some members are viviparous 

Scoliodon  Examples: Scoliodon (Dog fish), Pristis (Saw fish), Carcharodon (Great white shark), Trygon (Sting ray).
  • Marine or Fresh water
  • Ganoid, ctenoid or cycloid scales.
  • Presence of Anus.
  • 4 pairs of gills slits with operculum with swim bladder.
  • Without clasper
  • Usually external fertilization
  • Generally oviparous

Pristis Examples: Marine – Exocoetus (Flying fish), Hippocampus (Sea horse); Freshwater – Labeo (Rohu), Catla (Katla), Clarias (Magur); Aquarium – Betta (Fighting fish), Pterophyllum (Angel fish).

Super Class- Tetrapoda

16.  Amphibia

  • Live in aquatic as well as terrestrial-habitats.
  • Some are limbless (Icthyophis)
  • Some are with tail (Salamander)
  • Moist skin, without scales.
  • Presence of movable  lower eyelids.
  • Presence of tympanum, represents the ear.
  • Presence  of   cloaca (common opening for Alimentary Canal, urinary and  Reproductive tract).
  • Three chambered heart
  • Sexes are separate, fertilization external (except few salamander).
  • Oviparous
  • Indirect development (tadpolde larvae).
(a) Salamandra (b) Rana Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog),Salamandra (Salamander), Ichthyophis (Limbless  amphibia).

17.  Reptilia

  • Cornified skin with epidermal scales or scutes, presence of thoracic pulmonary breathing and amniotic egg are the most important terrestrial adaptation of reptiles.

    (a) Chameleon     (b) Crocodilus   (c) Chelone      (d) Naja
  • Creeping or Crawling mode of locomotion.
  • No external ear, tympanum represents the ear.
  • Mostly three chambered heart, four chambered in crocodiles.
  • Skin casting in snakes and lizards.
  • Separate sex and internal fertilization.
  • Usually oviparous, development direct.

Examples: Chelone (Turtle), Testudo (Tortoise), Chameleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator).Hemidactylus (Wall lizard), Poisonous snakes – Naja (Cobra), Bangarus (Krait), Vipera (Viper).

  • Poisonous snakes: Cobra, Krait, Viper, Pit viper, Russel viper, Sea snake, Coral snake and Rattle snake.
  • Non Poisonous Snakes: Python, Typhlops (Blind snake), Rat snakes, Tree snakes, double headed snakes.
  • 90%  of  snakes are nonpoisonous.
  • Neurotoxic Venom : It acts on nervous system, e.g., venom of Cobra, Krait and sea snakes.
  • Haemolytic Venom: It breaks down red blood corpuscles, e.g., venom of Viper.

18.  AVES

  • Presence of feather, pneumatic bones, and super-ventilated lungs (most efficient lungs) with air-sacs are the most adaptive feature of Aves.
  • Exoskeleton is epidermal; feathers form a non-conducting body covering for warmth, scales on the legs, similar to those of reptiles, claws on the toes, and sheaths on the beaks.
(a) Neophron   (b) Struthio
  • Skin is dry without glands except the oil gland (Preen Gland) at the base of the tail.
  • Body divisible into four distinct regions: head, neck, trunk and tail. Jawed bones prolonged into a toothless break or bill. Neck is long and flexible. Tail is short and stumpy.
  • Mouth is always bounded by a beak covered by horny sheath, edentulous (no teeth). Food storing crop and food masticating gizzard are present.
(c) Psittacula                 (d) Pavo
  • Limbs are two pairs. Forelimbs are modified as wings for flying. Hind limbs or legs are large, and variously adapted for walking, running, scratching, perching, food capturing, swimming.
  • Vertebral column short. Centra of vertebrae heterocoelous (saddle-shaped).
  • A synsacrum results by fusion of posterior thoracic, lumbar, sacral and anterior caudal vertebrae.
  • Tail vertebrae few, compressed laterally and the last 3 or 4 fused into a plough shape bone, pygostyle.
  • Sternum large, usually with a vertical, mid-ventral keel for attachment of large flight muscles.
  • Both clavicles and single interclavicle fused to form a V-shaped bone, called furcula or wishbone.
  • Pelvic girdle large and fused with synasacrum throughout its length.
  • Skull is monocondylic.
  • Larynx without vocal cords. A sound box or syrinx, produces voice.
  • Kidneys metanephric. Urinary bladder absent. Birds are uricotelic.
  • Male has a pair of abdominal testes. A copulatory organ absent except in ratitae, ducks, geese, etc. Female has a single functional left ovary and oviduct.
  • They are the first evolved warm-blooded animals.
  • Unisexual, strictly internal fertilization and oviparous.

Some birds :

Examples : Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).

Examples of Flightless Birds

1. African ostrich → Struthio

2. South American ostrich → Rhea

3. Cassowary → Casuarius

4. Emu Dromaius

5. Kiwi → Apteryx


  • Presence of Mammary glands, Hair.
  • External ear as pinna and glandular skin (sweat, sebaceous gland).
  • Presence of  diaphragm.
  • Pulmonary respiration.
  • Presence of bony endoskeleton. Skull is dicondylic. A single zygomatic arch present. Each half of lower jaw made of a single bone, the dentary.
  • Teeth are of several types (heterodont), borne is sockets (thecodont) and represented by two sets (diphyodont).
  • Heart 4-chambered with double circulation. Only the left aortic arch present. Renal portal system absent, R.B.C. small, circular and non-nucleated.
  • Kidneys metanephric. Excretion is ureotelic.
  • Sense organs well developed. Eyes protected by lids, the upper of which is movable. External ear opening protected by a large fleshy and cartilaginous flap called pinna. Middle ear cavity with 3 ear ossicles-malleus, incus and stapes. Cochlea of internal ear spirally coiled.
  • Sexual dimorphism generally well-marked. Male has an erectile, copulatory organ or penis. Testes commonly placed in a bag or scrotum outside abdomen.
  • Fertilization internal.
  • Parental care well developed.
Prototheria (oviparous) Theria (viviparous)
–  Egg laying mammal
–  Without placenta

–  Birth of young one
–  With placenta.
Theria Infraclass
(pouched mammals)
with  yolk sac placenta.
Example- Macropus
Eutheria (True placental Mammals)
With allanto – Chorionic placenta.
Example- Pteropus and Balaenoptera

Overall Example of Class Mammalia
Examples: Oviparous-Ornithorhynchus (Platypus); Viviparous – Macropus (Kangaroo), Pteropus (Flying fox), Camelus (Camel), Macaca (Monkey), Rattus (Rat), Canis (Dog), Felis (Cat), Elephas (Elephant), Equus (Horse), Delphinus (Common dolphin), Balaenoptera (Blue whale), Panthera tigris (Tiger), Panthera leo (Lion).

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