5.3 MOLLUSCS

5.3 MOLLUSCS

1. What are they like?

   • They have bilateral simmetry
   • They are aquatic or terrestrial
   • Thair body is divided in...
     • 1. A head that contains the sense organs
     • 2. A visceral mass containing the internal organs
     • 3. A muscular foot with different shapes
       • It is used to move, dig and catch prey
   • In most cases, they have a protective shell

2. Types

   • 1. GASTROPODS
     • They have a spiral shell
     • Their head is well-developed
     • large and very muscular foot
     • e.g. snail, slug, limpet
     • respiration
       • terrestrial by lungs
       • aquatic by gills
     • Mainly herbivores
   • 2. BIVALVES
     • They have a shell divided in two valves
     • Their head is not well defined
     • Their foot in the shape of a wedge
       • It is used to move and dig
     • They breathe through gills
     • Thay are filter feeders
     • e.g. mussel, clam, oyster
   • 3. CEPHALOPODS
     • They do not have a shell. Exception nautilus
     • They have two well-developed eyes in the head.
     • They do not have foot. They have tentacles
     • They breathe through gills
     • They are carnivores
     • e.g. squid, octopus and nautilus

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