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Phylum Mollusca: Molluscus-Soft


PHYLUM MOLLUSCA: MOLLUSCUS-SOFT


  • This group is comprised of soft bodied animals.
  • Habit and Habitat: they are free-living, aquatic animals that live in mostly sea water and some occur in fresh water.
  • Symmetry: they are bilaterally symmetric with little segmentation and without appendages.
  • Body cavity: True coelomic cavity is reduced, general body cavity is filled with blood. So it is known as hemocoel.
  • Body differentiation: They are multicellular, real developed organs are present.
  • Germ layer: They are triploploblastic animals.
  • Body organization: Body is divided into anterior head, ventral foot and hard dorsal visceral mass. Foot is mainly used for locomotion.
  • Skeleton:  Their body is supported with hard shell made up of calcium carbonate.
  • Life processes:
  1. Alimentary canal/ digestive tract is simple.
  2. Open blood circulatory system is present.
  3. Respiration occurs through body gills, mantle or lung type structures.
  4. Excretion takes place through kidney like structures.
  5. Sense organs are developed in some of them.
  6. They are unisexual. Reproduction is sexual with internal fertilisation.

 

Examples:

Chiton, octopus, unio, pila etc.