Molluscs
Study Guide
Mollusc Characteristics
• Coelom reduced
• Most viscera concentrated in dorsal visceral
mass
• Body covered by thick mantle (epidermis) which
forms a cavity
• Mantle secretes calcium carbonate shell (or
spicules)
• Large ventral muscular foot
• Radula (band of teeth in esophagus)
Class Bivalvia — Clams, etc.
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Body and foot laterally compressed
Shell with two hinged valves
Reduced cephalization
Edges of mantle usually fused to form siphons
Radula lost
Marine and freshwater; mostly filter-feeders
Kingdom: Animalia
Phylum: Mollusca
Class: Pelecypoda
Order: Eulamellibranchia
Family: Veneridae
Genus: Venus
Species: mercenaria
http://biog-101-104.bio.cornell.edu/BioG101_104/tutorials/animals/clam.html
Practice Slides
The next few slides have no
labels. Practice using the
following clam dissections.
Clam with one shell removed and
the underlying mantle still in place.
Internal features of the clam; the shell
and mantle have been removed to show
the foot and gills (ctenidia).
Internal anatomy of the clam, showing
mouth, stomach, intestine, heart,
pericardial cavity and musculature.
Internal features of the clam. The
foot has been opened to show the
digestive system and gonads.
Anterior end of the clam showing
the stomach and digestive gland.
Pericardial cavity of the clam
showing the heart and the intestine
passing through it. The atrium of the
heart is visible.
Internal anatomy of the clam showing the
posterior region. The cavity above the gills
leading to the excurrent siphon is visible.
View of the siphons
of the clam. The
incurrent is lower
and the excurrent is
uppermost. (WHY?)
The shell on the left
side has been
removed.
Class Cephalopoda — Squid,
etc.
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Shell chambered (if present), reduced, or absent
Prehensile tentacles surround mouth
Mouth with radula and beak
Muscular siphon provides jet propulsion
Well developed brain, eyes
Closed circulatory system
Marine
Kingdom: Animalia
Phylum: Mollusca
Class: Cephalopoda
Order: Teuthida
Family: Loliginidae
Genus: Loligo
Species: brevipenna
Notes
• Arms are for prey capture and transfer of
sperm to female by male.
• Tentacles are for holding prey after it is
captured.
• The pen is the remnant of what feature of
most molluscs?
• What are chromatophores used for?
esophagus
Same as Branchial Heart
Same as Branchial Heart
Male Squid
Male Squid
Squid Female
Squid Female
Squid Female
Squid Female
Squid Female
Squid Ganglia
Class Polyplacophora — Chitons
• Dorso-ventrally flattened and somewhat
elongated
• 8 dorsal shell plates (valves)
• Mantle forms thick lateral girdle (and sometimes
covers plates)
• Lack eyes, antennae
• Marine
Kingdom: Animalia
Phylum: Mollusca
Class: Polyplacophora
Order: Amphineura
Family: Mopaliidae
Genus: Katharina
Species: tunicata
Chitons
(Class: Polyplacophora)
Characteristics
• Dorso-ventrally flattened and somewhat
elongated
• 8 dorsal shell plates (valves)
• Mantle forms thick lateral girdle (and sometimes
covers plates)
• Lack eyes, antennae
• Marine
Chiton (Katharina tunicata)
Class Gastropoda — Snails &
Slugs
• Coiled, asymmetric shell (lost in many)
• Visceral mass (gut, nervous system)
becomes twisted 90-180°
• Muscular, flattened, creeping foot
• Head with eyes (may be reduced or lost),
tentacles
• Mantle highly vascularized; becomes lung
• Marine, freshwater, and terrestrial