Mollusk Life Cycle• Most mollusks are

dioecious (separate sexes)

• Some are hermaphroditic

• The life cycle of many mollusks includes a free swimming, ciliated larval stage called a TROCHOPHORE

Major Mollusk Classes• Four major classes

of mollusks:– Class

Polyplacophora – the chitons

– Class Gastropoda – snails & slugs

– Class Bivalvia – clams, mussels, oysters

– Class Cephalopoda – octopus & squid

Class Polyplacophora• Includes the

chitons• Eight overlapping

shell plates • Can roll up• All marine• Use radula to

scrape algae off rocks.

Class Gastropoda• largest of the

mollusk classes• 70,000+ named

species• Include snails, slugs,

nudibranchs (sea slugs), sea butterfly

• Marine, freshwater, terrestrial

• Creep along using foot

Class Gastropoda• The shell of a

gastropod is always one piece, called a valve.

• Gastropods are considered univalves

Class Gastropoda• Many snails

can withdraw into the shell and close it off with a lid called an operculum.

Class Gastropoda • Nudibranchs are

sea slugs– Do not have shell– Have colorful

branches of gut or gills exposed

– Prey on sponges, cnidarians, & other invertebrates

– May produce noxious chemicals

Class Gastropoda- Nudibranchs

Class Gastropoda- Nudibranchs

Gastropod Feeding Habits

• Most gastropods are herbivores and feed by scraping algae off of rocks using the radula.

• Some (like nudibranchs) are carnivores