Phylum Mollusca

Phylum Mollusca

Mollusks… - Possess an unsegmented soft body,

and most have a prominent shell. - occupy habitats ranging from the deep ocean to shallow waters to moist terrestrial niches. - Certain mollusks constitute important food staples, such as the shrimp.

- possess a flexible body wall, which surrounds a body cavity containing the internal organs. - The shell is formed by secretions of glandular cells in the mantle.

- Bilaterally Symmetrical. - Have circulatory, respiratory, digestive, excretory, nervous, & reproductive systems. - Most have separate sexes that cross-fertilize eggs.

General Features of Mollusks…

Mantle - Serves as “skin” surrounding visceral mass. - It’s outer surface secretes cells forming the shell. - It houses the respiratory organs. - Is adapted for swimming in Cephalopods.

Foot - Is the major characteristic used for classification. - Is adapted for LOCOMOTION. - Usually ventral, broad, flat and muscular.

Radul a food into the - Scrape mouth/ pharynx.

Shel l

- Secreted by the Mantle for protection.

3 Layers of the Shell Periostracu m - Protector

against erosions and Prismatic Thick calcium other animals. Layer Nacreouscarbonate - Responsible for Layer

Classes of Phylum Mollusc a

Gastropoda

… - Also called as UNIVALVES, having one shell. - Very striking in it’s diversification of habitats -During their larval life stages, all gastropods go through a bodychange process called torsion, or twisting.

-Includes snails and slugs …

Bivalvia

… - Commonly known as BIVALVES, having two shells. - These valves or shells are joined together by a hinge or ligament on it’s dorsal side. - These valves are also controlled by the retraction of the adductor muscles.

- The head and radula is not present in - Bivalves includes a Bivalves…wide variety of clams, oysters, mussels and scallops.

Cephalopod a

- it’s name basically means “ head foot” - Characterized by a completely merged head and foot. - Possess INK SACS which they use to evade predators.

- Known for their highly advanced nervous system.

- Most are carnivores that feed on fishes, crustaceans

- Number of tentacles range from

To…

90 !

8…

- All can swim, propelling themselves backwards by expelling water forcefully.

Importance of Mollusks…

- Used by humans as FOOD. - Oysters produce PEARLS. - Shells are used for jewelries and decorative purposes.

and some of it’s DISADVANTAGES… - Some do crop and garden DAMAGE. - Serve as intermediate hosts for some parasites such as flukes.