Phylum Mollusca
• This is the second largest animal phylum.
• Mollusca are terrestrial or aquatic (marine or fresh water)
• Exhibit organ system level of body organization.
• They are bilaterally symmetrical (except univalves) triploblastic and celomatic animals .
• Body is covered by a calcareous shell
• Unsegmented with a distinct head, muscular foot and a visceral hump or visceral mass.
• A soft layer of skin forms a mantle over the visceral hump.
• The space between the visceral mass and mantle is called mantle cavity
• A number feather like gills are present which ae respiratory in function.
• The digestive system is complete
• Mouth contains a rasping organ called radula
• With transverse rows of chitinous teeth for feeding radula is absent in bivalves.
• The sense organs are tentacles, eyes and ospharidium to test the purity of water and present in bivalves and gastropods.
• Excretory organs are nephridia
• open type of circulatory system is seen except for cephalopods such as squids , cuttle fishes and octopuses.
• Blood contains haemocyanin a copper containing respiratory pigment.
• They are diecious and oviparous.
• Development is indirect with a veliger larva.
Example : sepia, squid, devil fish, pila
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