PHYLUM MOLLUSCA

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PHYLUM MOLLUSCA
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• General Information
• Soft bodies usually protected by shell.
• True coelom
• Usually have 3 body regions
• a. Head/foot- locomotion retraction of body
  into shell.
• b. Mantle- thin skin layer covering visceral
  mass secretes shell.
• c. Visceral mass- organs for digestion,
  excretion, circulation, reproduction

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• Classification
• Kingdom Animalia
• Phylum Mollusca
• 3a. Class Gastropoda- snails, slugs
• 3b. Class Bivalvia- clams, oysters, mussels
• 3c. Class Cephalopoda- squid, octopus

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• IIIa. Class Gastropoda
• Snails, slugs
• Marine, freshwater,
• terrestrial
• 3. Largest most varied class
• 4. Some have shell- univalves (one shell)
• a. Apex- center spiral, oldest part of shell
• b. Operculum- door that closes shell to
  prevent dehydration.

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Apex
Eyespots
Shell
Pneumostome
Tentacle
Operculum
Mouth
Foot
Head/anterior
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• Locomotion
• 1. Wave-like contractions of muscular foot.
• 2. Lay down layer of mucus (terrestrial)

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• Digestion/Feeding
• 1. Have radula- tongue-like organ with
  tooth-like structures for scraping food.
• 2. Mostly herbivores (algae) some predators
  (cone snail- highly venomous)
• 3. Mouth, pharynx, esophagus, stomach,
  intestine, anus.
• 4. Salivary digestive glands help breakdown
  food

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• Respiratory System
• 1. Gills- aquatic
• 2. lungs/diffusion- terrestrial

• Circulatory System
• 1. Open circulatory system- blood leaves short
  vessels and bathes tissues directly in blood.
• 2. Pulmonary vein- conducts oxygen from gills
  to heart via blood.
• 3. Heart- pumps blood rich in oxygen to rest of
  body thru aorta.
• 4. Aorta- dumps blood into spaces around organs.

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• Excretory System
• 1. Nephridium- removes excess liquid waste,
  sends to mantle cavity where released to
  outside.
• 2. Aquatic- release liquid ammonia waste
• 3. Terrestrial- release uric acid in crystal
  form to prevent water loss.

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• Nervous/Sensory System
• 1. Six ganglia throughout body.
• 2. Sensory structures located at anterior end-
  most sensitive area-retreats into shell first.
• a. Anterior tentacle- at front of head
• b. Posterior tentacle- behind anterior
  antennae have eyes that detect light
• c. Osphradia- chemoreceptors that detect
  food and predators.

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• Reproductive System
• 1. Most are monoecious.
• 2. Can be protandric- testes develop first
  after they degenerate, ovaries mature.
• 3. Eggs are fertilized internally layed as
  sticky mass.
• 4. Some marine gastropods are dioecious.

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• Economic/Environmental Significance
• 1. Source of food (escargot)
• 2. Slugs destroy gardens/crops
• 3. Hosts for parasites of man (flukes)

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• IIIb. Class Bivalvia
• Clams, oysters, mussels, scallops.
• All marine or freshwater
• Second largest class
• All have 2 shells

• Locomotion
• 1. Clams/mussels- muscular foot for burrowing
• 2. Oysters- adults are sessile
• 3. Scallops- clap shell

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B. Shell Features 1. Shell structure a.
Periostracum- thin outer layer of protein b.
Prismatic layer- thick mid layer of calcium
carbonate c. Nacreous layer- inner layer
secretes nacre which forms pearls in some. 2.
Umbo- swollen area near anterior dorsal end of
clam oldest part of shell. 3. Hinge ligament-
holds two shells together 4. Growth lines-
wider lines indicate more growth/better feeding
season. 5. Anterior and Posterior adductor
muscles- very strong muscles for opening or
closing shell.
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C. Digestion/Feeding 1. Filter feeders 2.
Food/water enter incurrent siphon. 3. Food
swept into mouth by 2 pairs of palps 4.
Esophagus, stomach, intestine, anus 5.
feces/excess water leave thru excurrent siphon.
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D. Respiration 1. Oxygenated water enters
incurrent siphon. 2. Gills have tubes where
water blood are close together. Gases
exchange by diffusion across the membrane. 3.
Deoxygenated water leaves thru excurrent siphon.
E. Circulation 1. Open 2. Heart and short
vessels similar to gastropods.
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F. Excretion 1. Nephridium

• Nervous/Sensory System
• 1. Ganglia concentrated in foot, esophagus,
  adductor muscle and mantle.
• 2. Some have eyes for sensing light around
  shell rim.
• 3. Osphradia- chemoreceptors

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• Reproduction
• 1. Most are dioecious- external fertilization
• 2. Sperm leave thru excurrent siphon
• 3. Sperm brought in thru incurrent siphon of
  female.
• 4. Some release trochophore larvae which
  develop into adults.

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• 5. Some release glochidia which look like
  miniature adults.
• These are usually parasitic on fish.
• Attach to fish gills feed on blood.
• When adult organs form, they drop off take on
  filter feeding life style.

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• Economic/Environmental Significance
• 1. Source of food
• 2. Filter/clean water of harmful pollutants
• 3. Form pearls/jewelry
• 4. Mother of pearl buttons made from shells

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• PLEASE TURN IN
• Shell fish We Have Eaten Article Questions
• Clam Dissection Lab
• Exit Exam Diagnostic Test- scantron only
• Get the word splash off of my desk and use your
  notes to write a few logical paragraphs about the
  structure function of bivalves. Use the words
  on the front effectively and correctly. THIS IS
  A GRADE!

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Journal 3.2

• What are two examples of Gastropods and Bivalves
  (be sure to state which is which)

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• IIIc. Class Cephalopoda
• Squid, octopus, nautilus, cuttlefish
• All marine
• Most complex mollusk
• No external shell, have internal support
• a. Squid- have internal chitinous structure
  called pen

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b. Cuttlefish- have cuttlebone. Can be used
as calcium supplement for birds.
c. Chambered nautilus- has true shell
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d. Octopus- has no shell
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• Locomotion
• 1. All cephalopods can
• move by jet propulsion-
• forcefully expelling water from siphons on
  head.
• 2. Octopus crawl with arms.
• 3. Squid cuttlefish have posterior fins for
  steering/movement.

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• Digestion/Feeding
• 1. Have arms with suction cups to capture/hold
  prey.
• 2. Sharp beak for tearing into prey.
• 3. Radula for drilling holes in shells.
• 4. Use extracellular digestion- secrete enzymes
  that breaks down food before enters mouth.
• 5. Most nocturnal- eat
• crustaceans, fish,
• other mollusks, etc.

Radula
Beak
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Holes created by octopus radula. b indicates
where octopus gave up and used beak to break into
shell.
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• Respiratory System
• 1. Gills in mantle cavity
• Circulatory System
• 1. Closed- blood enclosed in blood vessels.
• Excretory system
• 1. Nephridia

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• Nervous/Sensory System
• 1. Large brains- good memory, can work thru
  problems.
• 2. Complex eye- very similar to human eye.
  Can form images and distinguish color

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• Camouflage
• a. Chromatophores- pigments cells in skin
  which allow color change. Can also use to
  communicate with other cephalopods (mating,
  aggression, fear, etc)
• b. Suckers on arms are very sensitive. Can
  change texture of skin to match rocks.

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• Ink gland
• ejects ink cloud when disturbed to make quick
  getaway.
• tyrosinase- also released to irritate predators
  eyes and
• paralyze sense of smell

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• Reproduction
• 1. Dioecious
• 2. Male testes package sperm in a case called
  a spermatophore.
• 3. He uses his enlarged tentacle-
  hectocotylus- to transfer spermatophore to
  females mantle cavity.
• 4. Female lays eggs which pick up sperm on the
  way out.

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• 5. Eggs are deposited in string-like masses in
  octopus den.
• Octopus brood young until they hatch. Keeping
  clean of debris.
• Young never cared for after hatching.

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• Economic/Environmental Significance
• 1. Food source- calamari, octopus
• 2. Bait for commercial fishermen
• 3. Can be pests in oyster beds- eating up all
  profit!

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• The Giant Squid

• 50 feet long weigh almost 1 ton
• Eats fish other squid and has been known to eat
  sperm whale calves

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