Transcript Mollusk PowerPoint

Mmmmm…Molluscs!
What mollusks have you eaten?
Who has eaten clams? Clam chowder
“On the half
shell”
Who has eaten squid? Calamari
What has eaten oysters?
Who has eaten snails? Escargot
Characteristics
Soft-bodied invertebrate covered with protective
mantle that may or may not form a hard, calcium
carbonate shell
Second largest animal phylum
Includes: chitons, snails, slugs, clams, oysters,
squid, octopus, and nautilus
Chiton
Slug
Snail
Clams
Oysters
Nautilus
Squid
Octopus
Characteristics
Have a muscular foot for movement which is
modified into tentacles for squid and octopus
Characteristics
Complete one-way digestive tract with a mouth
and anus (unidirectional)
Have a fully lined coelom (eucoelomates)
Characteristics
Cephalization – have a distinct head with sense
organs and brain
Have a scraping mouth-like
structure called the radula
Go through a free-swimming
larval stage called trocophore
Characteristics
Body organs called visceral mass lie below
mantle
Systems they have: circulatory, respiratory,
digestive, excretory, nervous, and reproductive
Bilaterally symmetrical
Characteristics
Most have separate sexes that cross-fertilize
eggs
Gills between mantle and visceral mass are used
for gas exchange
4 Classes of Mollusks
Polyplacophora: chitons
Gastropoda: snails, slugs, nudibranchs,
conches, abalones
Bivalvia (Pelecypoda): clams, oysters, mussels
Cephalopoda: squid, octopus, nautilus
Class Polyplacophora
All marine
Have a shell divided into 8 overlapping plates
Live on rocks along seashore
feeding on algae
Chitons are in this class
Class Gastropoda
Head has a pair of retractable tentacles with
eyes located at the ends
Have a single shell or valve (snails) or none
(slugs)
Known as univalves
VALVE = SHELL
Class Gastropoda: Snails
May be marine, freshwater, or terrestrial
Aquatic snails breathe through gills and use
their radula to scrape algae for food
Terrestrial snails use their mantle cavity as a
modified lung and also saw off leaves
Have an open circulatory system
Class Gastropoda: Snails
Land snails are hermaphrodites but do not
fertilize their own eggs
Aquatic snails have separate sexes
All snails use internal fertilization
Class Gastropoda:
Pteropods
Called “sea
butterflies”
Marine
Have a wing like flap
for swimming
Class Gastropoda: Oyster
Drills
Radula modified to
drill into oyster shells
Feeds on the soft
body inside the shell
Can be devastating
for commercial
shellfishing
Class Gastropoda:
Nudibranch
Marine slug
Lacks shell
Colorful
Class Bivalvia
(or Pelecypoda)
Sessile or sedentary (stays in one spot)
Includes marine clams, oysters, shipworms,
scallops, and freshwater mussels
Filter feeders
Have two-part, hinged shell (2 valves)
(valve=shell)
Class Bivalvia
(or Pelecypoda)
Have muscular foot that extends from shell for
movement
Scallops clap valves together to move
Class Bivalvia
(or Pelecypoda)
Shell secreted by mantle and made of 3 layers:
Outer hard layer protects against acids
Middle prismatic layer made of calcium carbonate
for strength
Inner pearly layer next to soft body
Mantle secretes substance called “mother of
pearl” to surround irritants like grains of sand
Class Bivalvia
(or Pelecypoda)
Mantle secretes substance called “mother of
pearl” to surround irritants like grains of sand
Oldest, raised part of shell called umbo
Class Bivalvia
(or Pelecypoda)
Powerful anterior and posterior adductor
muscles open and close shell
Lack a distinct head
Class Bivalvia
(or Pelecypoda)
Have an incurrent and excurrent siphon that
circulate water over the gills to remove food and
oxygen
Have heart and open circulatory system (no
veins/vessels for blood to flow through)
Nervous system made of 3 pairs of ganglia, nerve
cords, and sensory cells that detect light, chemicals,
and touch
Separate sexes with external fertilization of eggs
Class Cephalopoda
Includes octopus, squid, cuttlefish, and
chambered nautilus
All marine
Cuttlefish
Nautilus
Class Cephalopoda
Most intelligent mollusk
Well developed head
Active, free swimming predators
Octopus
Squid
Class Cephalopoda
Foot divided into tentacles with suckers
Use their radula and beak to feed
Closed circulatory system
Beak
Class Cephalopoda
Lack an external shell (except nautilus)
Highly developed nervous system with
vertebrate-like eyes
Separate sexes with internal fertilization
Class Cephalopoda—
Squid
Largest invertebrate is the Giant Squid
Large, complex brain
Ten tentacles with longest pair to catch prey
Use jet propulsion to move by forcing water out
their excurrent siphon
Class Cephalopoda—
Squid
Chromatophores in the skin can help change
squid color for camouflage
Can squirt an inky substance into water to
temporarily blind predators
Dark spots are
chromatophores
Class Cephalopoda—
Squid
Have internal shell called pen
Female lays eggs in jellylike material and
protects them until hatching
Class Cephalopoda—
Octopus
Eight tentacles
Similar to squid
Crawls along bottom looking for prey
Class Cephalopoda—
Chambered Nautilus
Has an exterior shell
Lives in the outer chamber of the shell
Secretes gas into the other chambers to adjust
buoyancy
Economic Importance
of Mollusks
Used by humans for food
Pearls from oysters
Shells used for jewelry
Do crop and garden damage
(especially snails)
Serve as intermediate hosts for some parasites such
as blood flukes