Phylum Mollusca
• soft bodied; many with protective shell
• more species of molluscs in ocean than any other
phylum, over 200,000 sp.
• the mantle is a thin tissue layer covering body that
secretes shell
• the foot allows locomotion or attachment
• most have a head with eyes
• the radula is a tooth like structure used for feeding
• Ancestral larvae is a trocophore; some produce a
veliger
• Open circulatory system
• gastropods, bivalves, cephalopods, and chitons
Larval Forms
Trocophore
Veliger
Class Gastropoda - snails
• “stomach foot”
• most have coiled, spiral,
shells (dextral or sinistral)
• many use radula to scrape
algae for food
• predatory snails’ radula is
modified to capture prey;
spear or drill
• also include nudibranchs and
sea hares
• Consist of the Subclasses
Prosobranchia (aquatic, gilled
snails), Opisthobranchia
(non-shelled), Pulmonata
(land, lung snails)
Figure 7.19
Coiling vs. tortion
Tulip Snail
Figure 7.20
Nudibranchs (of the Subclass
Opisthobranchia)
Figure 7.21d
• “naked gills”
• no shell
• often prey on cnidarian
polyps and sponges
• many are noxious tasting
or use nematocysts from
cnidarians for protection
Class Bivalvia
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•
•
•
•
•
laterally compressed
hinged shell
no radula, no head; filter feed by siphoning water
strong muscles close shell; scallops
clams burrow in mud or sand
Mussels (byssal threads) and oysters (cement) attach to
surfaces
• scallops live free; may move by flapping valves
• largest is giant clam
Figure 7.22a
Figure 7.22c
Figure 7.22d
A pearl is produced when a grain of sand or
other particle gets between delicate mantle
membrane and shell. The sand grain is
calcified and forms a pearl
Class Cephalopoda
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•
•
•
•
•
•
•
“head foot”
predatory, highly intelligent, very good vision
shell internal or absent
suckers on tentacles
beak like radula
use jet propulsion; siphon and funnel
can change color (chromatophores) and/or release ink
squid, octopus, cuttlefish, nautilus
Figure 7.24a
Figure 7.24b
Figure 7.24c
Figure 7.25a
A squid measuring about 60 feet (18
meters) washed up on a Tasmanian
beach over the weekend.
(CNN.COM)
Class Polyplacophora - chitons
• Attach tightly to rocks using
foot as suction cup
• Feed on algae
• Shell is made of hard
plates