Notes Class 11 Chapter 4 Biology Maharashtra Board

Kingdom Animalia

Introduction

The Kingdom Animalia encompasses a vast and diverse group of multicellular, eukaryotic organisms that are heterotrophic and lack cell walls. This chapter explores the systematic classification of animals based on their structural and functional characteristics, body plans, and evolutionary relationships.

1. Basis of Classification

• Definition: Classification is the process of grouping organisms based on shared characteristics to understand their evolutionary relationships and diversity.
• Basis for Classification:
  • Structural features: Body organization, symmetry, germ layers, and body cavity.
  • Developmental patterns: Embryonic layers (diploblastic or triploblastic).
  • Physiological traits: Digestion, circulation, and reproduction.
• Need and Importance:
  • Simplifies the study of diverse organisms.
  • Helps understand evolutionary relationships.
  • Facilitates identification and naming of species.
  • Aids in ecological and biological research.

2. Five Kingdom Classification

• Proposed by: Robert H. Whittaker (1969).
• Kingdoms: Monera, Protista, Fungi, Plantae, and Animalia.
• Animalia: Includes multicellular, heterotrophic organisms with no cell walls.

3. Criteria for Animal Classification

Animals are classified based on the following structural and organizational features:

3.1 Grades of Organization

• Cellular Level: Cells function independently with minimal division of labor (e.g., Porifera).
• Cell-Tissue Level: Cells form tissues for specific functions (e.g., Cnidaria).
• Tissue-Organ Level: Tissues form organs (e.g., Platyhelminthes).
• Organ-System Level: Organs work together in systems (e.g., Annelida onwards).

3.2 Body Symmetry

• Asymmetry: No plane of symmetry (e.g., Porifera).
• Radial Symmetry: Body can be divided into equal halves along any plane passing through the center (e.g., Cnidaria, Ctenophora).
• Bilateral Symmetry: Body can be divided into identical halves along one plane (e.g., Platyhelminthes onwards).

3.3 Body Cavity (Coelom)

• Acoelomate: No body cavity (e.g., Platyhelminthes).
• Pseudocoelomate: Body cavity not fully lined by mesoderm (e.g., Aschelminthes).
• Coelomate: True body cavity lined by mesoderm (e.g., Annelida onwards).

3.4 Germ Layers

• Diploblastic: Two germ layers (ectoderm and endoderm) (e.g., Cnidaria, Ctenophora).
• Triploblastic: Three germ layers (ectoderm, mesoderm, endoderm) (e.g., Platyhelminthes onwards).

3.5 Segmentation

• Unsegmented: Body not divided into segments (e.g., Platyhelminthes).
• Segmented: Body divided into repeating segments (e.g., Annelida, Arthropoda).

4. Animal Body Plans

4.1 Cell Aggregate Plan

• Description: Cells do not form tissues or organs; minimal differentiation.
• Example: Porifera (sponges).
• Features: Asymmetrical, cellular-level organization, no specialized digestive system.

4.2 Blind-Sac Body Plan

• Description: Body is sac-like with a single opening for ingestion and egestion.
• Example: Cnidaria (e.g., Hydra).
• Features: Radial symmetry, diploblastic, gastrovascular cavity for digestion.

4.3 Tube-Within-Tube Body Plan

• Description: Digestive system with separate mouth and anus within a body cavity.
• Example: Annelida onwards (e.g., fish).
• Features: Bilateral symmetry, triploblastic, complete digestive system.

5. Detailed Classification of Phyla

5.1 Phylum Porifera (Sponges)

• Examples: Scypha, Euspongia (bath sponge), Euplectella (Venus’ flower basket).
• Habitat: Mostly marine, some freshwater; sedentary.
• Features:
  • Asymmetrical, cellular-level organization.
  • Body with pores (ostia) and a central cavity (spongocoel); water exits through osculum.
  • Canal system for water circulation, aiding in feeding, respiration, and excretion.
  • Choanocytes (collar cells) line spongocoel, creating water currents.
  • Skeleton of calcareous/siliceous spicules or spongin fibers.
  • Reproduction: Asexual (fragmentation, gemmule formation) and sexual (internal fertilization, larval stage).
  • High regeneration ability.

5.2 Phylum Cnidaria

• Examples: Hydra, Aurelia (jellyfish), Physalia (Portuguese man-of-war).
• Habitat: Mostly marine, some freshwater; sessile or free-swimming.
• Features:
  • Radial symmetry, diploblastic, blind-sac body plan.
  • Two forms: Polyp (cylindrical, e.g., Hydra) and Medusa (umbrella-like, e.g., Aurelia).
  • Gastrovascular cavity (coelenteron) for digestion and circulation.
  • Tentacles with cnidoblasts (stinging cells) for anchorage, offense, and defense.
  • Reproduction: Asexual (budding, regeneration) and sexual (gamete formation, metagenesis in some, e.g., Obelia).
  • Metagenesis: Alternation of polyp and medusa stages.

5.3 Phylum Ctenophora (Comb Jellies)

• Examples: Pleurobrachia, Ctenoplana.
• Habitat: Exclusively marine, free-swimming.
• Features:
  • Radial symmetry, diploblastic, blind-sac body plan.
  • Tissue-level organization.
  • Eight rows of ciliated comb plates for locomotion.
  • Bioluminescence; colloblasts (sticky cells) for prey capture.
  • Reproduction: Sexual, indirect development.
  • Minor phylum due to few species.

5.4 Phylum Platyhelminthes (Flatworms)

• Examples: Planaria, Taenia (tapeworm), Fasciola (liver fluke).
• Habitat: Mostly parasitic, some free-living (e.g., Planaria).
• Features:
  • Bilateral symmetry, triploblastic, acoelomate.
  • Dorso-ventrally flattened body.
  • Organ-system level organization.
  • Parasitic forms with hooks and suckers; free-living forms with cilia.
  • Incomplete digestive system (blind-sac) or absent in parasites.
  • Flame cells (protonephridia) for excretion and osmoregulation.
  • Hermaphrodite, high regeneration in free-living forms.

5.5 Phylum Aschelminthes (Roundworms)

• Examples: Ascaris (roundworm), Wuchereria (filarial worm), Ancylostoma (hookworm).
• Habitat: Mostly parasitic, some free-living.
• Features:
  • Bilateral symmetry, triploblastic, pseudocoelomate.
  • Tube-within-tube body plan; long, cylindrical body.
  • Tough cuticle covering body; no circular muscles.
  • Complete digestive system with mouth and anus.
  • Excretion via canals or gland cells; nervous system with nerve ring.
  • Unisexual, sexual dimorphism in some (e.g., Ascaris).
  • Parasitic adaptations: Cuticle, hooks, and suckers.

5.6 Phylum Annelida (Segmented Worms)

• Examples: Nereis, Pheretima (earthworm), Hirudinaria (leech).
• Habitat: Aquatic, terrestrial, or ectoparasitic.
• Features:
  • Bilateral symmetry, triploblastic, coelomate.
  • Metameric segmentation; clitellum in some (e.g., earthworm).
  • Locomotion via setae, parapodia, or suckers.
  • Complete digestive system; closed circulatory system.
  • Nephridia for excretion and osmoregulation.
  • Nervous system with nerve ring and ventral nerve cord.
  • Mostly hermaphrodite, some dioecious (e.g., Nereis).

5.7 Phylum Arthropoda (Jointed Appendages)

• Examples: Cockroach, Butterfly, Scorpion, Millipede, Prawn.
• Habitat: Omnipresent; mostly free-living, some parasitic.
• Features:
  • Bilateral symmetry, triploblastic, coelomate.
  • Metameric segmentation; chitinous exoskeleton requiring periodic moulting (ecdysis).
  • Body divided into head, thorax, and abdomen.
  • Open circulatory system (haemocoel); respiratory organs (gills, trachea, book lungs).
  • Excretion via Malpighian tubules, green glands, or coxal glands.
  • Well-developed sense organs (antennae, compound eyes).
  • Unisexual, internal fertilization, direct or indirect development (metamorphosis in some).
  • Economic importance: Honey bees (honey, wax), silk worms (silk), edible species (prawns); harmful species (mosquitoes, locusts).

5.8 Phylum Mollusca (Soft-Bodied Animals)

• Examples: Pila, Octopus, Sepia (cuttlefish), Pinctada (pearl oyster).
• Habitat: Aquatic, terrestrial, or marshy; free-living or sedentary.
• Features:
  • Bilateral symmetry (some asymmetrical due to torsion), triploblastic, coelomate.
  • Body with head, foot, and visceral mass; mantle secretes calcareous shell.
  • Complete digestive system; radula (rasping organ) in buccal cavity.
  • Respiration via gills (ctenidia) or lungs; open circulatory system (except Sepia: closed).
  • Excretion by kidneys; nervous system with ganglia.
  • Unisexual, mostly oviparous, some with indirect development.
  • Economic importance: Edible molluscs, pearl production, calcium from shells.

5.9 Phylum Echinodermata (Spiny-Skinned Animals)

• Examples: Asterias (sea star), Cucumaria (sea cucumber), Antedon (sea lily).
• Habitat: Exclusively marine, benthic, solitary, or gregarious.
• Features:
  • Radial symmetry (pentamerous), triploblastic, coelomate.
  • Calcareous endoskeleton with ossicles and spines.
  • Water vascular system for locomotion, feeding, and respiration (madreporite entry).
  • Complete digestive system; respiration via gills, papillae, or respiratory tree.
  • No circulatory or excretory system; simple nervous system.
  • Unisexual, external fertilization, indirect development, high regeneration.

5.10 Phylum Hemichordata

• Examples: Balanoglossus, Saccoglossus.
• Habitat: Marine, bottom-dwellers, mostly free-living.
• Features:
  • Bilateral symmetry, triploblastic, coelomate.
  • Body divided into proboscis, collar, and trunk; buccal diverticulum (notochord-like).
  • Complete digestive system; respiration via gill slits.
  • Open circulatory system; excretion via glomerulus.
  • Unisexual, external fertilization, indirect development.
  • Connecting link between non-chordates and chordates due to notochord-like structure.

5.11 Phylum Chordata

• Characteristics:
  • Notochord (flexible rod) at some stage.
  • Dorsal hollow nerve cord.
  • Pharyngeal gill slits at some stage.
  • Ventral heart.
• Subphyla:
  • Urochordata (Tunicates):
    • Examples: Herdmania, Salpa.
    • Marine, covered by tunic (tunicine).
    • Notochord in larval tail, lost in adults.
    • Many gill slits; closed circulatory system.
    • Indirect development.
  • Cephalochordata (Lancelets):
    • Example: Branchiostoma (Amphioxus).
    • Marine, fish-like, buried in sediment.
    • Notochord throughout life; myotomes present.
    • Closed circulatory system; respiration via gill slits.
    • External fertilization.
  • Vertebrata:
    • Notochord replaced by vertebral column.
    • Divisions:
      • Agnathostomata (Jawless):
        • Class Cyclostomata (e.g., Petromyzon, Myxine).
        • Eel-like, no jaws, cartilaginous skeleton.
        • Ectoparasitic, circular sucking mouth.
        • Median fins, no paired fins.
      • Gnathostomata (Jawed):
        • Superclass Pisces (Fishes):
          • Poikilothermic, aquatic, streamlined body.
          • Lateral line system for water current detection.
          • Respiration via gills; two-chambered venous heart.
          • Classes:
            • Chondrichthyes (Cartilaginous Fishes):
              • Examples: Scoliodon, Pristis.
              • Marine, placoid scales, heterocercal tail.
              • No air bladder; internal fertilization, many viviparous.
            • Osteichthyes (Bony Fishes):
              • Examples: Labeo rohita, Exocoetus.
              • Cycloid/ctenoid scales, homocercal tail.
              • Air bladder for buoyancy; external fertilization, oviparous.
        • Superclass Tetrapoda:
          • Bear two pairs of limbs (some secondarily limbless).
          • Classes:
            • Amphibia:
              • Examples: Rana (frog), Bufo (toad).
              • Dual life (land and water), poikilothermic.
              • Moist skin, no exoskeleton; respiration via skin, lungs, buccopharynx.
              • Three-chambered heart; oviparous, external fertilization, metamorphosis.
            • Reptilia:
              • Examples: Naja naja (cobra), Testudo (tortoise).
              • Terrestrial, poikilothermic, epidermal scales.
              • Three-chambered heart (crocodile: near four-chambered).
              • Oviparous (some viviparous), internal fertilization.
            • Aves (Birds):
              • Examples: Columba (pigeon), Struthio (ostrich).
              • Homeothermic, feathers, pneumatic bones.
              • Four-chambered heart; oviparous, internal fertilization.
              • Single ovary/oviduct in females; no urinary bladder.
            • Mammalia:
              • Examples: Human, Macropus (kangaroo).
              • Homeothermic, mammary glands, hair/fur.
              • Four-chambered heart; mostly viviparous, some oviparous (e.g., Platypus).
              • Heterodont dentition, enucleated RBCs.

6. Key Points

• Non-Chordates vs. Chordates:
  • Non-chordates lack notochord, gill slits, and dorsal nerve cord.
  • Chordates have these features at some stage.
• Economic Importance:
  • Arthropods: Honey, silk, edible species; some pests.
  • Molluscs: Pearls, edible, calcium source.
  • Annelids: Vermicompost (earthworms).
• Evolutionary Trends:
  • From acoelomate to coelomate.
  • From open to closed circulatory systems (Annelida onwards).
  • From diploblastic to triploblastic.
  • Increasing complexity in nervous and sensory systems.