Phylum Mollusca

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Phylum Mollusca
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Phylogeny
Platyhelminthes
Mollusca
Arthropoda
Chordata
Porifera
Annelida
Cnidaria
Nematoda
Echinodermata
pseudocoelom
segmentation
acoelom
Protostome schizocoelem
Deuterostomes eucoelom
radial symmetry
bilateral symmetry
true tissue
no true tissues
Ancestral Protist
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Phylum Mollusca
Class Polyplacophora
Class Gastropoda
Class Bivalvia
Class Cephalopoda
chitons
Snails Sea slugs nudibranchs
Squid Octopus Cuttlefish Nautilus
clams
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Phylum Mollusca (mollis, soft)

• Over 90,00 living species
• 70,00 fossil species
• Some are herbivorous grazers
• Some are predaceous carnivores
• Many are filter feeders
• Some are parasites
• Mostly marine but some terrestrial and freshwater

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Phylum Mollusca Economics

• Many are used as food
• Culturing of pearls
• Shipworms burrow into wood destroying ships and
  wharves
• Snails and slugs are garden pests
• Some snails are intermediate host for parasites

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Form and Function Head-foot

• Head foot contains feeding, cephalic senory and
  locomotor organs at the anterior end.
• The head foot contains digestive, circulatory,
  respiratory and reproductive organs in the
  visceral mass

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Generalized Mollusc Anatomy
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Mantle Cavity

• Body usually an anterior head, ventral foot and a
  dorsal visceral mass.
• Covered by a fleshy outgrowth of the body wall
  called a mantle or pallium.
• Shell if present is secreted by the mantle
• Space between mantle and body is the mantle
  cavity.

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Head-Foot

• Well developed head with mouth and sensory
  organs.
• Photosensory receptors range from simple to
  complex eyes.
• Tentacles may be present.
• Posterior to the mouth is the locomotor organ,
  the foot.

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Radula

• Rasping tongue like organ
• Rows of tiny teeth-up to 250,000-pointed
  backward.
• Rasps off fine particles of food from surface.
• Acts as a conveyor belt to move particles to the
  digestive tract.

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Foot

• The foot is usually ventral.
• May be used for attachment to substratum
• May be used for locomotion
• Free-swimming forms have modified the foot into a
  wing or a fin-like swimming agents.

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Mantle and Cavity

• Mantle is a sheath of skin on side of body.
  Secretes shell when present.

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Systems

• Skeletal- Mantle may secretes a shell. Use
  hydrostatic pressure for ventral muscular foot.
• Muscles -Ventral muscular foot and other muscles
  present.
• Digestive- complete complex with salivary glands,
  digestive gland and Rasping tongue (Radula).
• Circulatory - Open except for Cephalopoda.
  Dorsal heart, usually in a pericardial cavity.
• Respiratory - Ctenidia (gills) in mantle cavity,
  respiratory pigment is copper.

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Systems

• Excretory- by nephridia usually connecting to the
  pericardial cavity,
• the coelom is usually reduced to the cavities of
  the nephridia, gonads and pericardium.
• Nervous - Nerve ring with various pairs of
  gangliatwo pairs of nerve cords, one innervating
  the foot, the other the visceral mass (modified
  ventral ladder-like system)
• Integumentary - Mantle
• Endocrine - nervous systems produces hormones.
• Reproductive - varied- monoecious, protandric, or
  dioecious. Larva in marine trochophore and
  veliger, in freshwater clam is glochidium.

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Taxonomy
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information of that taxon

• Classes
• Monoplacophora (no specimens)
• Polyplacophora
• Scaphopoda
• Gastropoda
• Bivalvia
• Cephalopoda

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Class Polyplacophora (Chitons)
Back to Taxonomy

• Elliptical body with dorsal surface bearing eight
  overlapping limy plates (valves)
• Chitons are marine.
• They live mostly in shallow water.
• All are similar in morphology and ecology.
• They are slow moving microphagous feeders,
  scraping algae and other small invertebrates from
  substrate with their radula.

• Genera
• Katherina
• Cryptochiton

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Polyplacophora representative genera.
Return to Polyplacophora

• Katherina

Katherina dorsal surface
Katherina ventral surface
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Polyplacophora representative genera.
Return to Polyplacophora

• Cryptochiton

Cryptochiton dorsal surface
Cryptochiton ventral surface
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Class Scaphopoda
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• Tooth shells (or Tusk shells)
• Shell and mantle slender, tubular, and slightly
  curved. It is open at both ends

Dentalium
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Class Gastropoda
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• Univalves, Shell usually spiral, distinct head,
  scraping radula.
• Visceral mass typically turned 180
  counterclockwise torsion. And the visceral mass
  is coiled in shell.
• Representatives
• Garden snail (Helix), Whelks (Busycon), Conch,
  Cowries,, Sea hare, Nudibranchs, Slugs, and
  abalone.

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Helix (garden snail)
Helix, ventral view
Helix, dorsal view
Return to Gastropoda
Helix, side view
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Busycon (Whelk)
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Busycon (shell removed)
Busycon shells
Busycon eggs
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Other Gastropods
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Abalone shells
Conch
Examples of gastropoda
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Other Gastropods (continues)
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Sea Hair side view
Sea Hair (ventral view)
Slug
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Class Bivalvia
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• Shell of two lateral valves, with dorsal hinge.
• Mantle of flattened right and left lobes.
  Posterior margin commonly forming siphons
• Labial palps beside mouth
• No head
• No radula

Representative bivalves
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Representatives of Bivalvia
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• Anadonta (Freshwater clam)
• Teredo (Shipworm)
• Rock boring clam
• Ostrea (Oyster)
• Pecten (Scallop)
• Freshwater clam dissection

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Anadonta
Return to Representatives
Dissection
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Teredo (shipworm)and the Rock boring worm
Return to Representatives
Teredo
Teredo in wood
Rock boring clam
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Oyster and Scallop
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Scallop shells
Oyster cluster
Oyster shells
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Freshwater Clam Dissection
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• External shell
• Mantle
• One mantle flap removed.
• Visceral Mass (not dissected)
• Dissected Visceral Mass I
• Dissected Visceral Mass II
• Dorsal Heart
• Dorsal heart I(showing auricle or atrium)
• Dorsal heart II(showing ventricle)
• Dorsal heart III (ventricle)

• Internal shell (showing muscle scars and pallial
  line)

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External Shell
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Mantle
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One side of mantle removed
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Visceral Mass
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Dissected Visceral Mass (I)
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Dissected Visceral mass (II)
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Dorsal Heart I
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Dorsal Heart II
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Dorsal Heart III
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Internal parts of shell Shell
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Class Cephalopoda
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• Large head with conspicuous eyes
• Ventral foot modified into tentacles(are arms)
  with suckers.
• Representative Cephalopods
• Nautilus(Chambered Nautilus)
• Octopus (Octopus)
• Loligo (Squid)
• Sepia (Cuttle fish)

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Nautilus
Return to Cephalopoda

• (South Pacific and Indian Ocean)

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Octopus
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• Eight arms

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Loligo
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Internal skeleton Pen
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Sepia
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• Cuttlebone (internal skeleton)

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Class Monoplacophora
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• First 10 specimens of Neopilina were taken in
  1952 from dark muddy clay at 3350 m(11,000 ft)
  off the coast of Costa Rica.
• Since then other species have been found in
  Indo-Pacific and South Atlantic Oceans.
• Neopilina is the only living genus
• Neopilina has segmented muscles