Quick Revision Notes

Class 11 Biology: Animal Kingdom (जंतु जगत)

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### Introduction & Basis of Classification

Animals (Metazoans) are multicellular, eukaryotic organisms without cell walls. They are classified based on certain fundamental features:

1. Levels of Organization (संगठन का स्तर):

   • Cellular Level (कोशिकीय स्तर): Cells are arranged as loose cell aggregates (e.g., Porifera).
   • Tissue Level (ऊतक स्तर): Cells performing the same function are arranged into tissues (e.g., Coelenterates).
   • Organ Level (अंग स्तर): Tissues are grouped to form organs specialized for a particular function (e.g., Platyhelminthes).
   • Organ System Level (अंग तंत्र स्तर): Organs associate to form functional systems (e.g., Annelids to Chordates).

2. Symmetry (सममिति):

   • Asymmetrical (असममित): Cannot be divided into equal halves (e.g., Sponges / Porifera).
   • Radial Symmetry (अरीय सममिति): Any plane passing through the central axis divides the organism into two identical halves (e.g., Coelenterates, Ctenophores, Echinoderms).
   • Bilateral Symmetry (द्वipārśviya सममिति): Can be divided into identical left and right halves in only one plane (e.g., Annelids, Arthropods, Chordates).

3. Germ Layers (जनन स्तर):

   • Diploblastic (द्विजननस्तरी): Animals in which cells are arranged in two embryonic layers—external ectoderm and internal endoderm (e.g., Porifera, Coelenterates). Mesoglea is present in between.
   • Triploblastic (त्रिजननस्तरी): Animals in which the developing embryo has a third germ layer, mesoderm, in between ectoderm and endoderm (e.g., Platyhelminthes to Chordates).

4. Coelom / Body Cavity (देहगुहा):

   • Acoelomate (अगुहिक): Body cavity is absent; space is filled with mesenchyme (e.g., Platyhelminthes).
   • Pseudocoelomate (कूटगुहिक): Mesoderm is present as scattered pouches in between ectoderm and endoderm; true coelom is not lined by mesoderm (e.g., Aschelminthes / Roundworms).
   • Coelomate (प्रगुहिक): Body cavity is lined by mesoderm all around (e.g., Annelida to Chordata).

5. Segmentation (खंडीभवन):

   • The body is externally and internally divided into segments (metameres) with a serial repetition of at least some organs. Seen in Annelida (earthworm), Arthropoda, and Chordata.

6. Notochord (पृष्ठरज्जु):

   • A mesodermally derived rod-like structure formed on the dorsal side during embryonic development in some animals.
   • Chordates: Have notochord.
   • Non-Chordates: Do not form notochord (e.g., Porifera to Echinodermata).

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### Classification of Phyla

1. Phylum Porifera (Sponges / स्पंज)

• Habitat: Mostly marine, asymmetrical.
• Key Feature: Water transport or canal system. Water enters through minute pores (ostia) in the body wall into a central cavity, spongocoel, from where it goes out through the osculum.
• Special Cells: Choanocytes or collar cells line the spongocoel and canals.
• Skeleton: Spicules or spongin fibers.
• Reproduction: Hermaphrodite; internal fertilization, indirect development.
• Examples: Sycon (Scypha), Spongilla (Freshwater sponge), Euspongia (Bath sponge).

2. Phylum Coelenterata / Cnidaria (Cnidarians / सीलेंटरेटा)

• Key Feature: Presence of cnidoblasts or cnidocytes (stinging capsules) on tentacles for anchorage, defense, and capture of prey.
• Symmetry: Radial, Diploblastic, Acoelomate.
• Body Forms: Exhibit two basic body forms—Polyp (sessile and cylindrical, e.g., Hydra, Adamsia) and Medusa (umbrella-shaped and free-swimming, e.g., Aurelia / jellyfish). Alternation of generation occurs in some (Metagenesis, e.g., Obelia).
• Examples: Physalia (Portuguese man-of-war), Adamsia (Sea anemone), Pennatula (Sea-pen), Gorgonia (Sea-fan), Meandrina (Brain coral).

3. Phylum Ctenophora (Comb Jellies / सीनेटोफ़ोरा)

• Key Feature: Commonly known as sea walnuts or comb jellies. Bear eight external rows of ciliated comb plates which help in locomotion.
• Property: Bioluminescence (the property of a living organism to emit light) is well-marked.
• Reproduction: Sexual only, fertilization external, indirect development.
• Examples: Pleurobrachia and Ctenoplana.

4. Phylum Platyhelminthes (Flatworms / चपटे कृमि)

• Key Feature: Dorso-ventrally flattened body; mostly endoparasites in animals including human beings.
• Symmetry: Bilaterally symmetrical, triploblastic, acoelomate, with organ level of organization.
• Special Structures: Hookers and suckers are present in parasitic forms. Flame cells help in excretion and osmoregulation.
• Reproduction: Hermaphrodite, fertilization internal, development through many larval stages. Planaria has high regeneration capacity.
• Examples: Taenia (Tapeworm), Fasciola (Liver fluke), Planaria.

5. Phylum Aschelminthes (Roundworms / गोल कृमि)

• Key Feature: Circular in cross-section (hence roundworms). Pseudocoelomate, triploblastic, organ-system level.
• Digestive System: Complete with a well-developed muscular pharynx.
• Excretion: An excretory tube removes body wastes through the excretory pore.
• Sexes: Dioecious (sexes are separate); females are generally longer than males. Internal fertilization, direct or indirect development.
• Examples: Ascaris (Roundworm), Wuchereria (Filarial worm), Ancylostoma (Hookworm).

6. Phylum Annelida (Segmented Worms / एनेलिडा)

• Key Feature: Body surface is distinctly marked out into segments or metameres; metameric segmentation.
• Symmetry: Bilaterally symmetrical, triploblastic, organ-system level, coelomate.
• Locomotion: Longitudinal and circular muscles help in locomotion. Aquatic annelids like Nereis possess lateral appendages, parapodia, which help in swimming.
• Circulatory System: Closed circulatory system.
• Excretion: Nephridia help in osmoregulation and excretion.
• Neural System: Pair of ganglion connected by lateral nerves to a double ventral nerve cord.
• Examples: Nereis, Pheretima (Earthworm), Hirudinaria (Blood-sucking leech).

7. Phylum Arthropoda (Largest Phylum / आर्थ्रोपोडा)

• Key Feature: Animals with jointed appendages (Arthro = joint, poda = appendge). Covered by a chitinous exoskeleton.
• Body Division: Head, thorax, and abdomen.
• Respiratory Organs: Gills, book gills, book lungs, or tracheal system.
• Circulatory System: Open type.
• Sensory Organs: Antennae, eyes (compound and simple), statocysts (balance organs).
• Excretion: Malpighian tubules, green glands, or coxal glands.
• Examples:
  • Economically important: Apis (Honey bee), Bombyx (Silkworm), Laccifer (Lac insect).
  • Vectors: Anopheles, Culex, Aedes (Mosquitoes).
  • Living fossil: Limulus (King crab).

8. Phylum Mollusca (Second Largest Phylum / मोलस्का)

• Key Feature: Soft-bodied animals, usually unsegmented with a distinct head, muscular foot, and visceral hump. Covered by a calcareous shell.
• Mantle: A soft and spongy layer of skin forms a mantle over the visceral hump. The space between the hump and mantle is the mantle cavity in which feather-like gills are present.
• Mouth: Contains a file-like rasping organ for feeding, called radula.
• Examples: Pila (Apple snail), Pinctada (Pearl oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea hare), Dentalium (Tusk shell), Chaetopleura (Chiton).

9. Phylum Echinodermata (Spiny-skinned Animals / इकाइनोडर्मेटा)

• Key Feature: Endoskeleton of calcareous ossicles (spiny skin). Adult echinoderms are radially symmetrical, but larvae are bilaterally symmetrical.
• Unique System: Presence of a water vascular system which helps in locomotion, capture and transport of food, and respiration.
• Excretory System: Absent.
• Reproduction: Sexes are separate, reproduction is sexual, fertilization is usually external, development is indirect with free-swimming larva.
• Examples: Asterias (Starfish), Echinus (Sea urchin), Antedon (Sea lily), Cucumaria (Sea cucumber), Ophiura (Brittle star).

10. Phylum Hemichordata (हेमीकॉर्डेटा)

• Key Feature: Formerly considered a sub-phylum under chordata, now treated as a separate phylum. Worm-like marine animals with an organ-system level of organization.
• Body Structure: Divided into proboscis, collar, and trunk.
• Circulatory System: Open type.
• Respiration: Gills.
• Excretory Organ: Proboscis gland.
• Examples: Balanoglossus (Acorn worm) and Saccoglossus.

11. Phylum Chordata (कॉर्डेटा)

• Fundamental Characteristics (All 3 must be present at some stage):
  1. Presence of a notochord.
  2. A dorsal, hollow, and single neural cord.
  3. Paired pharyngeal gill slits.
• Other features: Bilaterally symmetrical, triploblastic, coelomate with organ-system level of organization. Post-anal tail present.

Sub-phyla of Chordata:

• Urochordata (Tunicata): Notochord present only in larval tail (e.g., Ascidia, Salpa, Doliolum).
• Cephalochordata: Notochord extends from head to tail region and is persistent throughout life (e.g., Amphioxus or Branchiostoma).
• Vertebrata: Notochord is replaced by a cartilaginous or bony vertebral column in the adults. All vertebrates are chordates, but all chordates are not vertebrates.

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### Vertebrata Classification (कॉर्डेटा का उपसंघ- कशेरुकदंडी)

A. Class Cyclostomata (साइक्लोस्टोमेटा)

• Jawless vertebrates (Agnatha).
• Sucking and circular mouth. 6-15 pairs of gill slits for respiration.
• Cranium and vertebral column are cartilaginous. Marine, but migrate for spawning to fresh water.
• Examples: Petromyzon (Lamprey) and Myxine (Hagfish).

B. Class Chondrichthyes (Cartilaginous Fishes / उपास्थिल मछलियाँ)

• Marine animals with cartilaginous endoskeleton.
• Mouth is ventrally located. Notochord is persistent throughout life.
• Gill slits are separate and without operculum (gill cover).
• Skin is tough, containing minute placoid scales.
• Air bladder is absent, hence they have to swim constantly to avoid sinking.
• Examples: Scoliodon (Dogfish), Pristis (Sawfish), Carcharodon (Great white shark), Trygon (Sting ray).

C. Class Osteichthyes (Bony Fishes / अस्थिल मछलियाँ)

• Both marine and freshwater with bony endoskeleton.
• Mouth is mostly terminal. Four pairs of gills covered by an operculum on each side.
• Skin is covered with cycloid/ctenoid scales.
• Air bladder is present which regulates buoyancy.
• Heart is 2-chambered (one auricle, one ventricle). Cold-blooded (poikilothermous). Sexes are separate.
• Examples:
  • Marine: Exocoetus (Flying fish), Hippocampus (Sea horse).
  • Freshwater: Labeo (Rohu), Catla (Catla), Clarias (Magur).
  • Aquarium: Betta (Fighting fish), Pterophyllum (Angel fish).

D. Class Amphibia (एम्फिबिया / उभयचर)

• Can live in aquatic and terrestrial habitats.
• Body divisible into head and trunk (tail may be present in some).
• Skin is moist, without scales. Eyes have eyelids. Tympanum represents the ear.
• Alimentary canal, urinary, and reproductive tracts open into a common chamber called cloaca which opens to the exterior.
• Respiration by gills, lungs, and skin. Heart is 3-chambered (two auricles, one ventricle).
• Examples: Bufo (Toad), Rana (Frog), Hyla (Tree frog), Salamandra (Salamander), Ichthyophis (Limbless amphibian).

E. Class Reptilia (सरीसृप)

• Creeping or crawling mode of locomotion. Body covered by dry and cornified skin, epidermal scales or scutes.
• Tympanum represents ear. Snakes and lizards shed their scales as skin cast.
• Heart is usually 3-chambered, but 4-chambered in crocodiles.
• Poikilotherms (cold-blooded). Sexes are separate, fertilization is internal.
• Examples: Chelon (Turtle), Testudo (Tortoise), Chamaeleon (Tree lizard), Calotes (Garden lizard), Crocodilus (Crocodile), Alligator (Alligator), Hemidactylus (Wall lizard).
• Poisonous Snakes: Naja (Cobra), Bungarus (Krait), Vipera (Viper).

F. Class Aves (Birds / पक्षी)

• Presence of feathers and most of them can fly except flightless birds (e.g., Ostrich).
• Forelimbs are modified into wings. Hind limbs generally have scales and are modified for walking, swimming, or clasping.
• Skin is dry without glands except the oil gland at the base of the tail.
• Endoskeleton is fully ossified (bony) and the long bones are hollow with air cavities (pneumatic bones) to make body light.
• Digestive tract has additional chambers: crop and gizzard.
• Heart is 4-chambered. Homoiothermous (warm-blooded) animals—they can maintain a constant body temperature. Respiration by lungs.
• Examples: Corvus (Crow), Columba (Pigeon), Psittacula (Parrot), Struthio (Ostrich), Pavo (Peacock), Aptenodytes (Penguin), Neophron (Vulture).

G. Class Mammalia (स्तनधारी)

• Presence of mammary glands (milk-producing glands) by which the young ones are nourished.
• Skin has hairs. External ears or pinnae are present.
• Different types of teeth present in the jaw (Heterodont). Heart is 4-chambered.
• Respiration by lungs. Homoiothermous. Sexes are separate and fertilization is internal. Most are viviparous (give birth to young ones) except a few.
• 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).