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Molluscs
Origin of the word mollusc: From the Latin word
Mollis meaning soft
Animals in this phylum include: Snails, Octopus,
Squid, clams,
Level of organization: Organ
Symmetry: Bilateral
Coelomate (inner body cavity coated by
mesoderm)
General mollusc body plan
Characteristics of molluscs
1) Visceral mass: Soft body containing vital
organs:
-intestines
-kidneys
-nerve ganglia
2) Foot: strong, muscular organ used for
locomotion
3) Mantle: Membrane or muscle that envelopes
the visceral mass. Some secrete exoskeletons
Exoskeleton
Exoskeleton: A hard structure secreted by the
mantle.
Function of exoskeleton:
1) Protection (clam)
2) Structural (squid)
3) Preventing waterloss (snails)
Three Major Classes of Mollusc
1) Gastropods : Gastro = stomach
Pod = foot
Stomach foots
Common examples: abalone, nudibranchs, slugs
and snails
Gastropod
Characteristics:
1) Foot flattened ventrally
2) Move via muscle contractions in
the foot
3) Have one valve (shell) or no valves
4) Breath via the capillary network in
the mantle
Gastropod reproduction:
- Hermaphrodites but not capable
of asexual reproduction
Three Major Classes of Mollusc
2) Cephalopoda: Cephal = head poda = foot
head foot
Common examples: Squid, cuttlefish, nautilus and
octopus
Cephalopods
Characteristics:
1) Tentacles used to capture prey
2) Sharp beak used to dismantle prey
3)
Cephalopods
Characteristics:
1) Tentacles used to capture prey
2) Sharp beak used to dismantle prey
3) Radula (wrasping tonge)
4) Cephalization
5) Eyes: Contain lens and retina with
photoreceptors. NOT RELATED TO EYES IN
OTHER PHYLA
Cephalopods
Characteristics:
1) Tentacles used to capture prey
2) Sharp beak used to dismantle prey
3) Radula (wrasping tonge)
4) Cephalization
5) Eyes: Contain lens and retina with
photoreceptors. NOT RELATED TO EYES IN OTHER
PHYLA
6) Brain consisting of fused ganglia
7) Move via jet propulsion
Three Classes of Molluscs
3) Bivalve: Valve = shell, Bi = in two pieces
Common examples: Clams, Scallops, and
Mussels
Bivalves
Characteristics:
1) Shell made from two parts secreted by the
mantle
2) Shell made from protein or calcium carbonate
3) Sessile filter feeder
Bivalve Anatomy
Function of Parts
Parts
Function
Foot
movement, digging
Gill
gas exchange, catches particles and uses its
cilia to move it to the mouth
Adductor muscle
Keep the shell closed
Stomach
Digests food
Circulatory System
Open Circulatory system:
- Heart pumps water through the whole body
cavity. No tubes carrying blood.
- Less efficient then a closed circulatory system.
Nervous System
- Contains three ganglia connected by nerves
- Note: No cephalization in bivalves = no
concentration of nerves in one area
Digestive System
- Consist of: esophagus, Stomach, intestine,
labial palps, anus
- Excretory system contains two kidneys
Assignment
• Vocab 635-638
• Summary Table
• Check on Planaria