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mollusks (lophotrochozoans) anatomy: muscular foot
large muscle at base of animal
used for movement
modified as digging appendage in bivalves
modified to form tentacles for crawling/grasping in cephalopods
snails & chitons
works as a muscular hydrostat: hydrostatic skeleton
waves of muscle contractions sweep backward/forward to allow crawling across surface
mollusk anatomy: visceral mass
includes internal organs & external gill
separate from muscular foot
coelom
highly reduced in most mollusks
functions: reproduction & excretion of wastes
organs occupy different body cavity: hemocoel
body fluids bath organs directly in circulatory system
diff from coelom—not lined in mesodermal & has distinct development origin
radula
unique to mollusks
is a feed structure in mouth
at the anterior end of visceral mass
moves back & forth over food source
lost in bivalves, which acquire food by suspension feeding
mollusk anatomy: mantle
enclosure, a outgrowth of body wall that covers visceral mass
secretes a shell made of calcium carbonate
valves: 1, 2, or 8 eight parts in a shell
in bivalves, protective shell is hinged & closes
adaptations:
terrestrial snails: mantle forms internal lung
bivalves: mantle lined w/ muscle & forms siphons: tubes
cephalopods: mantle forms siphon that functions in jet propulsion
jet propulsion in
