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Mollusks
Zebra Mussels
Invaded Great Lakescame from Great Britain
Reproduce quickly-one
female releases 40,000
Cause problems-clog
intake pipesCompetition for other
organisms
Clean water since filter
feeders
Characteristics
1. Have a head/foot - elongated with an
anterior head-contains mouth and
sensory system-foot used for locomotion
and attachment
2. Visceral Mass - contains the organs
3. Have a Mantle – outer covering and
enfolds most of the body
Cont…
Coelome - fluid filled body cavity
Primary induction one of the three
primary tissues interacts with another
(endo, meso, ecto)
Cont…
No segmentation
Bilateral symmetry
Veliger
Organs systems for circulation, respiration,
digestion, and excretion
Trochophore (stationary) or Veliger (free
Trochophore
swimming found in gastropods and bivalves)
larvae
INFO
Respiration - most mollusks breath with
gills (ctenidium) located in their mantle
cavity (space between mantle and visceral
mass)– visceral mass contain the organs
– Mantle - heavy fold of tissue wrapped around
the visceral mass
Sexuality – Diecious, hermaprhoditic
– Pulmonate snail – “cupets arrow”
Circulation - three chambered heart and
Most have open circulatory system-(blood
leaks out of vessels and bathes the body’s
tissues directly, i.e. no capillaries, blood
vessels connected to sinuses)
Closed circulatory system - octopus and
squid-blood never leaves vessels
(capillary system).
Excretion nephridia (cilia that beat) rid
the mollusk of waste-
Mantle secrets a calcareous shell that
protects the visceral mass
– In bivalves this process helps in the
production of pearls.
History
Cambrian time 570 MYA
Brachiopods, cephalopods, and
gastropods
Cephalopods in shell
Three Major Classes
Bivalves
Gastropods
Cephalopods
Bivalves
sessile (stationary) filter feeders.
Two part hinged shell with a hinge keeping
it together
No distinct head region
Siphons-used to filter sea water for food
Reproduce sexually-male, female,
hermaphrodite-external fertilization
2nd stage of larvae is called veliger
Bivalve cont…
Oysters, scallop, clam, mussel
Oldest part of shell and bump is called umbo
Adductor muscles hold shell together (also
called a ligament)
If a grain of sand or parasite become lodged
between shell and mantle then the mantle
secrets a layer of material around the particle
forming a pearl
Umbo
Gastropods
Snails and slugs
Marine, freshwater, terrestrial
Head, foot, visceral mass, and mantle
Foot used for locomotion
Tentacles on head where eyes are located
Single shell
Gastropods cont…
Respiration either by gills, skin, or lungs
Radula rasping tongue that scraps food
Undergo torsion or twisting of the shell
180°
External & internal fertilization
Have Trochophore and veliger (free
swimming) larvae
Cephalopods
Means head and foot
Foot has evolved into
tentacles
Octopus, squid,
nautilus, cuttlefish
Use siphons for jet
propulsion
Cephalopods Cont…
Have beak for eating
Closed circulatory
system
Large brain and eyecan learn
Have pigment cells
(chromatophores) in
epidermis to
camouflage
Cephalopod
Nautilus
Cuttle
Squid
Octopus
Shell Hardness Speed Intelligence Color Change Ability
1 (external)
3
3
4
2 (internal)
2
2
1
3 (internal)
1
4
3
4 (none)
4
1
2
Nautilus
Cuttlefish
Interesting
ClassPolyplacophora
Chiton reduced head and flattened foot
Shell is divided into 8 parts
Feed on algae
External fertilization but no veliger stage
Homework
Why would you expect the blood pressure
inside most mollusk’s blood vessels to be
quite low?
Contrast the feeding habits of
cephalopods with those of gastropods.
Squids are the fastest swimmers of all
aquatic invertebrates. Name two
structural adaptations in squids that may
have enhanced their swimming ability.