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MOLLUSKS
Defining Characteristics of Mollusk
 Soft-bodies animals
 Internal or external shell
 Ex: snails, slugs, clams, squids, & octopi
Diversity
Very diverse, but similar developmental
stages
Trochophore: free-swimming larval stage
A: cillia
B: mouth
C: anus
Form and Function
Body Plan:
Foot: flat structure for crawling
Mantle: thin tissue layer covering body
Shell: made by glands
Visceral mass: internal organs
Feeding: herbivores, carnivores, filter
feeders, detritivores, or parasite
Radula: flexible tongue-like structure with 100’s
teeth
Form and Function
Circulation
Open: blood pumped through vessels with a
simple heart
Closed: transports blood quicker
Respiration: gills or with mantle cavity
Excretion: nephridia remove ammonia
Response to stimuli: large variance
Movement: jet propulsion & secrete mucus
along base of foot
Groups of Mollusks
 Gastropods: shell-less or single shelled, move
by muscular foot
snails, slugs, sea butterflies
 Bivalves: two shells held together by powerful
muscles
Clams, oysters, mussels, & scallops
Groups of Mollusks
 Cephalopods:
soft-bodied
Head: attached to a single foot
Foot: divided into tentacles or arms
Octopi, Squids