Chitons, Snails, Slugs, Mussels, Oysters, Clams, Squid, Octopus Phylum Mollusca Chitons, Snails, Slugs, Mussels, Oysters, Clams, Squid, Octopus
Phylum Mollusca Characteristics 50,000 living species “soft body” Bilateral symmetry First coelomates All organs present and well developed Gills or lungs Open circulatory system with heart
More Characteristics First coelomates: space lined with mesoderm; and organs suspended by mesodermal membranes called mesenteries Gives support and protection to organs
More Characteristics Gills or lungs in addition to exchange through body surfaces Respiration and circulation are advanced enough to permit large size Largest invertebrates at 18 m. and 450 kg.
More Characteristics Mantle: secretes a shell in most cases; is a sheath of skin that is often a pair of folds Radula: a rasping tongue-like organ with tiny teeth Foot: muscular sole mostly for locomotion Sensory organs including touch, smell, taste, equilibrium, and vision Vision is especially keen in cephalopods
Snail Radula radula
Classification
The Major Classes
Gastropods Snails (shell) Slugs Only terrestrial mollusks are in this class Freshwater and marine
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Class Pelecypoda Bivalves No terrestrial Freshwater and marine Filters small organic particles from the water Scallop
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Class Polyplacophora Chitons Flattened, elongated Graze on algae 7 or 8 dorsal shell plates
Class Cephalopoda Squid, Octopus, nautilus, cuttlefish Fastest, most intelligent invertebrates Closed circulation Predators
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Cuttlefish Nautilus
Baby Octopus