PHYLUM MOLLUSCA

1
PHYLUM MOLLUSCA

• Page 340 - 344

2
General Information

• Soft-bodied invertebrates
• Live on land or in the water
• Most have a head with eyes and sensory cells that
  receive stimuli from the environment
• Due to soft body, they need protection so have
  shells that act as a shield and prevent bodies
  from drying out
• One of the largest animal phyla
• Clams, oysters, scallops, squid, slugs, snails,
  and octopuses (octopi)

3
Physical Characteristics

• Bilateral symmetry
• Most have one or more shells
• All organ systems

4

• Body Plan
• a. Muscular foot lower part of most
  mollusks used for locomotion (crawling or
  digging) and the foot aides in the capturing of
  food
• b. Head mouth, sense organs, ganglia
  (brain)
• c. Visceral Mass MOST OF THE BODY
  contains the heart and other organs
• ( see visceral mass)
• d. Mantle fleshy tissue / soft and
  strong tissue two purposes 1. protects
  organs
• 2.
  produces a hard
• 
  shell

5

• Soft Body
• Reproduce - How?
• sexually
• separate sexes
• sperm released in water
• sperm swept to eggs under mantle
• fertilization

6
Visceral Mass (animals internal organs)

• Digestive System continuous tube mouth to anus
• Circulatory System includes blood vessels and a
  heart transports food and oxygen to all part
  of the body
• or
• Gills some that live in water have
  specialized organs called gills take oxygen out
  of water and put into blood

7

• Nervous System well developed brain and nerve
  fibers
• enable mollusks to perceive and react to
  surroundings
• Eyes

8
3 Main Classes

• Gastropoda 1 shell or none
• stomach foot
• snail and slug
• Bivalvia 2 shells
• hatchet foot
• clams, oyster, scallops,
  mussels
• Cephalopoda no shell
• head foot
• squid, octopus
• categorized based on the kind of foot
  (structure and location) and whether or not they
  have a shell

9
Gastropoda page 342 and Snail page 343

• Stomach foot broad flat foot on the bottom
  surface / helps in locomotion / glides on mucus
  produced by the foot
• Most single shell / some with no shell
• Radula sharp tongue (scraper like) tongue
  like organ with rows of teeth used for scraping
  and tearing food apart to eat
• Examples snails 1 shell / slides on foot
• slug no shell / snail
  with out a shell
• limpet
• shell is usually one part

10
Bivalviapage 342-344

• Live in the ocean and some in fresh water
• Sources of food
• two valves (shells) 2 parts or valves hinged
  at the back
• Filter feeders get food by opening shell and
  filter tiny animals and food from the water
• Hatchetfooted wedge shaped foot for digging
  and to burrow into the soft sand/mud
• Separate sexes
• Examples Clam, oyster, scallops, mussels 2
  shells with a hinge

11
Cephalopodapage 344

• Meat eating animals
• No external shell except for squid
• head footed forms arms or tentacles lined
  with suction cups (at head) to capture prey and
  for movement
• Highly developed brain and eyes (like humans)

12

• Predators
• Speed jet propulsion squirt a stream of water
  from body propel the animal backwards
• Tentacles to capture prey
• Examples
• squid small internal shell
• octopus no shell / large eyes
• cuttlefish and nautiluses