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Mollusks and
Annelids
Kingdom Animalia
Phylum Mollusca
Gastropods, Bivalves, Cephalopods
General Characteristics
• Trochophore – larval stage of development
• Two body regions
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– Head-foot – contains the head (mouth & sensory organs) &
the foot (locomotion)
– Visceral Mass –contains the vital organs covered by mantle
which secretes CaCo3 to make the shell.
Bilateral symmetry w/cephalization
The use of gills to exchange gas.
Nephridia are used to remove metabolic waste
Two types of circulation
– Open circulatory- blood moves through vessels & into open
spaces around body organs
– Closed circulatory – blood is enclosed entirely in vessels.
Class Gastropoda
• Gastropods – “stomach foot”
• Snails, abalones, conchs, slugs,
nudibranchs, sea butterflies, sea
hares, periwinkles, whelks,
limpets, cowries, and cones
• Use radula-tongue like strip used
to scrap food.
• Open circulatory system with
two-chambered heart.
• Found in freshwater, saltwater &
moist terrestrial habitats
• Land type use modified mantle to
respire and water type use gills.
Class Bivalvia
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Bivalves-two halves of shells.
Clams, oysters, scallops
Open circulatory system
Shell made of CaCO3 w/ mother
of pearl inside
• Filter feeders that are usually
sessile can move w/foot
• Incurrent & excurrent siphons to
move water into and out of the
body for respiration w/gills and
for feeding
• Mostly separate sexes w/external
fertilization
Size ranges from 1mm to 1.5 m
Class Cephalopoda
• “Head-foot”-squid, octopus,
nautilus, cuttlefish
• Closed Circulatory system
• Internal fertilization
• Largest brain of invertebrates
• Well-developed sensory
organs
• Use of jet propulsion, ink
sprays & camouflage
Class Cephalopoda
• Squid – 8 arms & 2
tentacles-catching prey
• Octopi – 8 arms
• Nautilus – 90 arms
• Largest – Giant Squid up
to 60 feet long
• Nautilus only one
w/outer shell, others have
small internal shells
called pens.
Photo of Colin Dunlop's cuttlefish chomping on a fish
Phylum Annelida
• Segmented worms
• Bilateral symmetry
w/cephalization
• Live in soil, freshwater,
and the sea.
• External bristles-setae
• Most have welldeveloped organ systems
(Photo G. Brändle)
Class Oligochaeta
• Earthworms -Live in soil & freshwater.
• Ingest soil as they burrow through
• Circular & longitudinal muscles w/100 identical
segments.
• Hermaphroditic – internal fertilization. The
clitellum aids in reproduction
• Respire through their skin so must stay moist.
• Use nephridia to excrete waste
• Bilateral symmetry w/cephalization
Pathways
Food pathway
mouth - pharynx - esophagus - crop (storage)-gizzard
(grinding)-intestines-anus.
The waste of earthworms is called castings.
Circulatory pathway
The blood travels to posterior via ventral blood vessel
& returns to anterior via dorsal blood vessel w/aortic
arches acting as a heart
Class Polychaeta
• Sandworms, fanworms,
bloodworms, lug worms,
plumed worms, sea mice
• Free-living marine predators
• Contain a pair of appendages
called parapodia which are
used for gas exchange,
swimming and crawling.
• Have antennae and specialized
mouthparts
Class Hirudinea
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Leeches
Moist tropical areas
Parasitic
Powerful suckers both
ends with no setae
• Uses anesthetic to
prevent host from feeling
• Can swallow 5x weight
in blood
Cottobdella epshteini S.Utevsky, 1997