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Download Mollusca Mollusca: Variety
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4/20/2011 Mollusca •Milestone = Coelom •True Body Cavity •Characteristics •Larval Stage = Trochophore Mollusca: Variety •Three Classes •Gastropoda •Ex. Pond snails, Land slugs •Either shell-less or have a single spiral-shaped shell •Move using a ventral foot •Cephalopoda •Ex. Octopi, squids •Most active mollusks •Soft-bodied, no shell or has a hard internal shell •Head is attached to a single foot that divides into tentacles •Bivalvia •Ex. Clams, oysters, mussels, scallops •Have two shells •Focus for this Phylum 1 4/20/2011 Clam: Body Form & Skeleton •Exoskeleton •Body Plan •Foot – muscular region on bottom used for locomotion •Contains mouth, radula (tongue), and teeth •Visceral Mass – area that surrounds organs •Mantle – cape of heavy tissue outside organs, located right underneath the shell •Shell – created by the glands in the mantle •Two shells, held together by two powerful muscles Clam: Digestion •Filter Feeders •Cilia and mucus on the gills trap food particles •Water enters the clam through the incurrent siphon •And leaves through the excurrent siphon •Gastrointestinal Tract Mouth Stomach Intestine Anus 2 4/20/2011 Clam: Respiration, Circulation, Excretion •Respiration •Breathe using gills inside of the mantle cavity •Circulation •Open Circulatory System •Blood is pumped by a simple heart that moves oxygen and nutrients throughout the body •Leaves and enters the heart through different sinuses •Large sac-like spaces •Excretion •Nephridia •Removes ammonia from the blood Clam: Nervous System •Simple Nervous System •Small ganglia near the mouth •Several nerve cords •Simple sense organs (eyespot) 3 4/20/2011 Clam: Reproduction •Reproduce Sexually •External Reproduction •Clams release a large amount of eggs and sperm into the water •Eggs are fertilized and develop into free-swimming larvae •Trochophore 4
