Wednesday, July 29, 2020

Animal Kingdom - Notes | Class 11 | Part 5: Mollusca, Echinodermata, Hemichordata

4. ANIMAL KINGDOM

PHYLUM MOLLUSCA (SOFT BODIED ANIMALS): GENERAL CHARACTERS

Mollusca is the second largest phylum.

  1. Grades of organization:
    • Organ system.
  2. Symmetry:
    • Bilateral symmetry.
  3. Germ layers:
    • Triploblastic.
  4. Coelom:
    • Coelomate.
  5. Habit and habitat:       
    • Aquatic.
    • Few are terrestrial.
  6. Digestive system:          
    • Complete.
  7. Respiratory system:
    • Gills in aq. forms and pulmonary sac in terrestrial forms.
  8. Circulatory system:
    • Open type.
  9. Reproduction:
    • Dioecious.
    • Oviparous.
    • Development is direct or indirect.
  10. Unique features:
    • Body has head, visceral mass (visceral hump) & muscular foot.  Head has sensory tentacles.
    • Calcareous shell.
    • Feather-like gills for respiration & excretion.
    • Mantle & radula are seen.
    • Mantle (Pallium): The membrane which covers visceral mass. Space between the hump and mantle is called mantle cavity.
    • Radula: File-like rasping organ present in the mouth of molluscs. It is used for feeding.
  11. Examples:
    • Pila (Apple Snail), Pinctada (Pearl Oyster), Sepia (Cuttlefish), Loligo (Squid), Octopus (Devil fish), Aplysia (Sea Hare), Dentalium (Tusk shell), Chaetopleura (Chiton).

PHYLUM ECHINODERMATA (SPINY SKINNED ANIMALS): GENERAL CHARACTERS

  • Grades of organization:
    • Organ system.
  • Symmetry:
    • Adults radial. Larvae bilateral.
  • Germ layers:
    • Triploblastic.
  • Coelom:
    • Coelomate.
  • Habit and habitat:
    • Exclusively marine.
  • Digestive system:
    • Complete.
    • Ventral mouth and dorsal anus.
  • Respiratory system:
    • Dermal branchiae (skin gills or papulae) and tube feet.
  • Circulatory system:
    • Open type.
  • Reproduction:
    • Dioecious.
    • External fertilization.
    • Development is indirect.
    • Ciliated free-swimming larva.
  • Unique features:
    • They have an endoskeleton of calcareous ossicles (Spiny bodied).
    • Head absent.
    • Water vascular system present.
    • Water vascular (ambulacral) system: In this system, sea water enters through a porous plate called madreporite and reaches the radiating canals and tube feet (podia). Its functions are locomotion, respiration, capture & transport of food and excretion.
    • Excretory system absent.
    • Shows autotomy & regeneration.
  • Examples:
    • Asterias (Starfish), Echinus (Sea Urchin), Echinocardium, Antedon (Sea Lily), Cucumaria (Sea Cucumber), Ophiura (Brittle Star).
PHYLUM HEMICHORDATA: GENERAL CHARACTERS

Hemichordata was earlier considered as a sub-phylum of Chordata. Like chordates, it has pharyngeal gill slits.
  • Grades of organization:
    • Organ system.
  • Symmetry:
    • Bilateral.
  • Germ layers:
    • Triploblastic.
  • Coelom:
    • Coelomate.
  • Habit and habitat:
    • Exclusively marine.
  • Digestive system:
    • Complete.
  • Respiratory system:
    • Gills.
  • Circulatory system:
    • Open type.
  • Reproduction:
    • Dioecious.
    • External fertilization.
    • Development is indirect.
  • Unique features:
    • Worm-like cylindrical body formed of anterior proboscis, a collar and a long trunk.
    • Collar bears stomochord (a rudimentary structure similar to notochord).
    • Excretion by Proboscis gland.
  • Examples:
    • Balanoglossus (Tongue worm), Saccoglossus.

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