MOLLUSCS

MOLLUSCS

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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: OrganSymmetry: 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

ExoskeletonExoskeleton: A hard structure secreted by the

mantle.

Function of exoskeleton:1) Protection (clam)2) Structural (squid)3) Preventing waterloss (snails)

Three Major Classes of Mollusc1) Gastropods : Gastro = stomach Pod = foot Stomach footsCommon examples: abalone, nudibranchs, slugs

and snails

GastropodCharacteristics:1) Foot flattened ventrally2) Move via muscle contractions in the

foot3) Have one valve (shell) or no valves4) Breath via the capillary network in the

mantle

Gastropod reproduction:- Hermaphrodites but not capable of asexual reproduction

Three Major Classes of Mollusc2) Cephalopoda: Cephal = head poda = foot head footCommon examples: Squid, cuttlefish, nautilus and

octopus

Cephalopods

Characteristics:1) Tentacles used to capture prey2) Sharp beak used to dismantle prey3)

Cephalopods

Characteristics:1) Tentacles used to capture prey2) Sharp beak used to dismantle prey3) Radula (wrasping tonge)4) Cephalization5) Eyes: Contain lens and retina with photoreceptors.

NOT RELATED TO EYES IN OTHER PHYLA

Cephalopods

Characteristics:1) Tentacles used to capture prey2) Sharp beak used to dismantle prey3) Radula (wrasping tonge)4) Cephalization5) Eyes: Contain lens and retina with photoreceptors.

NOT RELATED TO EYES IN OTHER PHYLA6) Brain consisting of fused ganglia7) Move via jet propulsion

Three Classes of Molluscs

3) Bivalve: Valve = shell, Bi = in two pieces Common examples: Clams, Scallops, and

Mussels

BivalvesCharacteristics:1) Shell made from two parts secreted by the

mantle2) Shell made from protein or calcium carbonate3) 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