4 Major Classes of Phylum Molluska

Class Polyplacophora

Body:

Shell:

Foot:

Head:
Example:

Body: elongated, flat.

Shell: 8 overlapping plates.

Foot: well-developed.

Head: reduced.

Example: chitons.

Class Gastropoda

Body:

Shell:

Foot:

Head:
Example:

• Body twisted (torsion).

• Shell: coiled, reduced, or absent.

• Foot: flattened.

• Head: well-developed.

  • Examples: snails, slugs.

Class Bivalvia

Body:

Shell:

Foot:

Head:
Example:

• Body: laterally flattened.

• Shell: two valves (left & right).

• Foot: hatchet-shaped.

• Head: reduced/absent.

• Examples: clams, oysters.

Class Cephalopoda

Body:

Shell:

Foot:

Head:
Example:

• Body: elongated for swimming.

• Shell: reduced, absent, or chambered (Nautilus).

• Foot: modified into arms/tentacles.

• Head: highly developed (cephalized).

• Examples: octopus, squid, nautilus.

How do the shells and heads differ among Gastropoda, Bivalvia, and Cephalopoda?

Gastropods: coiled/reduced shell, head developed.

Bivalves: two valves, head reduced/absent.

Cephalopods: shell reduced/absent/chambered; head highly developed with tentacles.

List the main feeding types of gastropods

Predators: oyster drills, whelks, moon snails

Scavengers: periwinkles

Grazers: limpets