Key to Phylum Mollusca

Taken primarily from  Kozloff, 1987, 1996  (Copyright 1987, 1996, University of Washington Press.  Used in this web page by permission of University of Washington Press)

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1a	Flattened body has 8 dorsal shell plates, usually visible dorsally.  Attach to rocks	Class Polyplacophora, Chitons
1b	Body does not have 8 dorsal shell plates, may or may not be flattened	2
2a	Body laterally compressed, has two valves hinged together dorsally.  Head rudimentary but often have large foot and gills	Class Bivalvia, Clams
2b	Body does not have two valves hinged together dorsally	3
3a	One shell, tubular, curved in less than 1/2 circle and opening on both ends, tapered so that one end is considerably smaller than the other	Class Scaphopoda, Tusk shells
3b	Shell not as above	4
4a	Have 8 to 10 tentacles with suckers instead of a creeping foot.  No external shell (in our area), but may have a reduced, internal shell.  Mouth has a beak.  Large, complex eyes not on stalks	Class Cephalopoda, Squid, Octopus
4b	No shell, or have a single shell which is curved into a spiral, a pyramid, or ear-shaped (in our area).  Crawl on muscular creeping foot.	Class  Gastropoda:  5
5a	Gastropods with shells	Snails, limpets (Class Gastropoda,  with shells)
5b	Gastropods without shells	Nudibranchs and  other Opisthobranchs