Atono,y of Mollusca

ammonoids animal aperture appear attached become bivalves Bivalvia blood body burrowing called Cambrian cephalopods chamber chitons closely coiled collected common complete considered consists contains cuttlefish deposits developed digestive diverse divided dorsal early edge evolved example exhalent extends extinct eyes feeding Figure foot forms fossil frequency freshwater ganglia gastropods gills gland hard head holed indicates infaunal inhalent internal Kissonerga known land lateral layer length limpets Linnaeus living located mantle cavity marine mass means Middle molluscs Monoplacophora mouth muscle muscular mussels occur Order Ordovician organs original pair particles passed period Polyplacophora possess posterior present primitive probably produce radula range recent relatively remains represented retractor samples Scaphopoda secretes shape shell side similar single snails soft species squid stomach structure studies style suggests surface Table tentacles Unionidae usually valves visceral wall