Class Bivalvia

1
Class Bivalvia

• The Two-Shelled Mollusks
• Zoology

2
Class Bivalvia

• Mollusks in the Class Bivalvia are also known as
  Pelecypoda, or hatchet-footed animals.
• They are bivalves, which means that they have two
  shells.
• They range in size from tiny seed shells that are
  1 to 2 mm in length to the giant South Pacific
  Clams, which are more than 1 meter in length and
  weigh more than 500 pounds!

3
A Bivalve Dinner

• Bivalves are mostly filter feeders. This means
  that they use the water currents created by cilia
  on their gills to bring in food materials from
  the water.
• Bivalves DO NOT have a head or radula. So they
  can only eat very small food particles.

4
Bivalve Homes

• Bivalves mostly live in marine aquatic
  environments.
• However, some also live in the freshwater aquatic
  environments of lakes , ponds , and streams .

5
The Bivalve Body

• The two shells (or valves) of a bivalve are held
  together on the dorsal side of the animal by a
  hinge ligament.
• You can tell the age of the bivalve by finding
  the umbo , or oldest part of the shell. Growth
  occurs in concentric, ringed lines around the
  umbo like the growth lines on the trunk of a
  tree.

6
Bivalves in Motion

• Bivalves have one foot that they can stick out
  between their shells. They pump blood into
  their foot and cause it to swell and anchor into
  the sand. Muscles then contract to pull the
  blood out of the foot and pull the animal forward
  .
• Scallops and file shells can move by
  flapping their shells together

7
Exchange of Gases in Bivalves

• Bivalves use their mantle and gills to
  filter oxygen from the water.

8
Making Baby Bivalves

• Most bivalves are unisex animals . This means
  that they are male or female .
• They typically reproduce externally.
• However, freshwater clams reproduce
  internally. Eggs drop in the water tubes of
  the gills and are fertilized by sperm that
  enter with the water flow.

9
Why Should Humans Care About Bivalves?

• Shipworms can actually bore into hard
  surfaces like wood or stone. They are very
  destructive if they move into shipyards .
• Humans like to eat bivalves . The oyster ,
  scallops , and clams have long been a
  staple in the human diet. Their shells are also
  used to make decorative items like jewelry .

10

• Zebra mussels can clog the intake and outtake
  pipes of industrial plants. They were
  introduced into the Great Lakes of North America
  by ships from northern Europe in 1986. By
  1994, these pests had increased their residential
  area to the Mississippi River Delta in New
  Orleans . They eat phytoplankton, which is an
  important food source for other aquatic animals.
  The control of this invasive pest will cost
  the United States billions of dollars.

11
The Pearl Industry

• The cultured_ pearl industry is vital to Japan
  and other regions of the world. The Japanese
  economy _ is an important part of the
  worlds economy and affects the economy of other
  countries .