Phylum Mollusca

• It is the second largest phylum.
• Habitat - Molluscs are terrestrial or aquatic; they may be marine or fresh water.
• Level of organization - They have an organ-system level of organization.
• Body symmetry - Bilaterally symmetrical.
• Body wall - triploblastic. Coelomate animals.
• Body is covered by a calcareous shell.
• Body is unsegmented, they have a distinct head, muscular foot and visceral hump.
• The radula - Mouth of the molluscs contain tongue-like organ called radula, which has many rows of teeth, which is used to scrape food.
• Mantle - It is a fold of skin that surrounds the body organs.
• It is a soft and spongy layer of skin that forms a mantle over the visceral hump.
• The space between the hump and the mantle is called the mantle cavity.
• Feather like gills are present in this cavity.
• These gills have respiratory and excretory in functions. Anterior head region has sensory tentacles.
• Example: Pila, Octopus, Pearl oyster, Loligo, Sea-hare, Chiton
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