Chapter 35Section 1Molluska

Characteristics of Mollusks

• Some are filter-feeders while others are fast-moving predators with complex nervous systems

• Coelomates- true body cavity

Characteristics of Mollusks

• Aquatic mollusks have a larval stage of development called a trochophore

• Trochophores are motile and disperse throughout bodies of water

Body Plan of Mollusks• 2 main regions- head-foot &

visceral mass• Head-foot- consists of the head,

mouth, sensory structures, and foot- large muscular organ usually used for locomotion

Body Plan of Mollusks• Visceral mass- (located above

the head-foot) contains the heart, organs of digestion, excretion, & reproduction

• Visceral mass is covered by a layer of epidermis called the mantle

Body Plan of Mollusks• Most mollusks- mantle secretes

hard shells containing calcium carbonate

• Why have a shell???

Body Plan of Mollusks• Mantle cavity- space between the

mantle and visceral mass• Gills are protected by mantle

cavity

Body Plan of Mollusks• Ganglia- more complex nervous

system that controls locomotion, feeding, and sensory information (light, touch, etc)

Body Plan of Mollusks• Radula- main feeding adaptation• Tongue-like strip of tissue covered

with tough, abrasive teeth that point backwards

• Terrestrial snails- cut through leaves

• Aquatic snails- scrape algae

Class Gastropoda• Gastropods

–snails, conchs–slugs & nudibranchs

Snail

Conch

Slug

Nudibranch

Class Bivalvia• Bivalves- two shells connected by

a hinge• Closes its shell with adductor

muscles, when the muscles relax, the valves open

• Most bivalves are sessile

Class Bivalvia• Clams• Bury in sand or mud• Feeding: Cilia beats on the gills

and set up a current of water that enters through the incurrent siphon and leaves though the excurrent siphon

Clam

Class Cephalopoda• Cephalopod- “head foot”• Free-swimming & have tentacles• Nervous system is advanced-

cephalopod brain is largest invertebrate brain

• Ex: Octopi can perform tasks & distinguish between objects

Class Cephalopoda• Release dark fluid to distract

predators• Chromatophores- pigment cells

that allow the organism to change colors quickly

Squid• Move by pumping in water though

their siphons • Largest invertebrate- Architeuthis-

60 feet long and up to 2,000 lbs!

Octopus

REVIEW!!!• What purpose does a radula

have?• Describe the characteristics of

mollusks.• Name the three major classes of

mollusks & an example of each.