Phylum Mollusca


 
 
Concept Explanation
 

Phylum Mollusca

Phylum Mollusca: Molluscs are soft-bodied, unsegmented, bilaterally symmetrical animals. This is the second largest group of animals after arthropods.

  • It has a very ancient fossil record.
  • The body has three parts: a head, a dorsal hump containing the internal organs and a ventral muscular foot. The dorsal hump is covered by a soft covering called the mantle, which secretes a calcareous shell. The animal retreats into this shell for protection.
  • Many molluscs have gills called ctenidia, for the exchange of gases. 
  • Terrestrial molluscs do not have gills. The space between the mantle and body wall, called mantle cavity, acts as the lungs.
  • Some marine molluscs lack eyes and tentacles, while most terrestrial molluscs have these.
  • Most molluscs have a rasping, tongue-like organ called radula for feeding.
  • They also have digestive gland called hepatopancreas.
  • The circulatory system is open.
  • Renal organs (like kidneys) lie close to the heart and help in excretion. 
  • Reproduction in molluscs is sexual. Usually the sexes are separate, though some animals are hermaphrodites.
  • Snails (Helix, Limnaea, Pila), mussels (e.g., Unio), conches (Strombus), limpets (Patella), oysters, clams, octopuses are all molluscs. The shells of oysters, clams, scallops, etc., have two halves hinged in the middle.
  • Members of the genus Chiton have 8 pieces of shell. Cuttle fish (Sepia), octopuses and squids (Loligo) have ink sacs. They squirt this ink to confuse the prey and predators. Giant squids are the largest invertebrates.
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    Sample Questions
    (More Questions for each concept available in Login)
    Question : 1

    In case of Molluscs the space between the mantle and body wall, is called as _____________________ .

    Right Option : A
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    Explanation
    Question : 2

    Pearls are produced by the animals of phylum _______________.

    Right Option : C
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    Explanation
    Question : 3

    The organism shown in the figure also known as the devil fish is the member of ________________  phylum.

    Right Option : B
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    Explanation
     
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