Download Mollusks and Annelids

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Mollusks and Annelids
Bio II
Rupp
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Phylum Mollusca Characteristics
• Mollusk—from the Latin
meaning “soft”
• Many have hard shells for
protection
• Approx. 112,000 species
• Range from sedentary feeders
to fast moving predators
• Coelomates
▫ Muscles can move without
affecting gut
▫ Circulatory system is not
interfered with
• Trochophore—larval stage
▫ Free-swimming
▫ Mouth and anus
▫ Cilia for movement and food
gathering
▫ Annelids and mollusks both
have, which shows common
ancestry
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Trochophore
Mollusk and annelid larval stage
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Mollusk Body Plan
• Two main regions
▫ Head-foot
 Contains sensory organs in head
 Foot contains muscle for locomotion
▫ Visceral mass
 Contains heart, digestive organs, excretion organs,
and reproduction organs
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Mollusk Body Plan con’t.
• Coelom around heart
• Mantle covering the visceral
mass—aka—epidermal layer
• Mantle secretes CaCO3
▫ Shells protect, but decrease
surface area
▫ Gills evolved
▫ Gills are protected by mantle
cavity
• Bilateral symmetry—apparent
in nervous system
• Ganglia are connected by
nerve cords
▫ Light
▫ Touch
▫ Chemicals
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Mollusk Body Plan con’t.
• Radula
▫ Main feeding adaptation
▫ Tongue-like strip covered in backwards facing
teeth
▫ Adapted to mollusk lifestyle
 Terrestrial snails eat grass
 Aquatic snails eat algae or drill shells
 Cone shell has a harpoon-like radula
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Mollusk Body Plan con’t.
• There are 8 classes, we will
focus on 3
▫ Gastropoda
▫ Bivalvia
▫ Cephalopoda
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Table 37-1
Feature
Gastropoda
Bivalvia
Cephalopoda
External shell
One in most
species, none in
slugs and
nudibranchs
Two
None except
chambered
nautilus
Head
Yes
No
Yes
Radula
Yes
No
Yes
Locomotion
Most crawl
Most are sessile
Rapid swimming
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Class Gastropoda
• Gastro means “stomach” and
poda means “foot”
• 90,000 species
• Snails, abalones, conchs—one
shell
• Slugs and nudibranchs—no
shell
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Class Gastropoda con’t.
• Torsion—the twisting process
that relocates the mantle
cavity
▫ Occurs in larval development
▫ Places mantle cavity near the
head
▫ Allows head to be retracted
▫ Coiling of the shell is
unrelated
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Class Gastropoda con’t.
• Movement occurs by wave-like
contractions of the foot
• Open circulatory system
▫ Hemolymph
▫ Hemocoel—blood cavity
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Snails
• Terrestrial, marine, and
freshwater
• Eyes on the end of tentacles—
they can retreat into head
• Gill-breathers
• Land snails have modified gills
for gas exchange
▫ Need to stay moist
▫ Dormancy—mucous plug—
prevents desiccation
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Slugs
• Respire through modified
mantle cavity
• Live in moist shady places to
prevent desiccation
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Nudibranchs
•
•
•
•
Marine
No shell
Name means “naked gill”
Respiration occurs across the
entire body
• Numerous extensions create
greater surface area
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Pteropods
• Name means “wing foot”
• Use the foot to swim instead of
crawl
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Class Bivalvia
• Name means “two shells”
• Clams, oysters, scallops
• Adductor muscles for closing
their shells
▫ Contraction closes
▫ Relaxation opens
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Class Bivalvia con’t.
• Each valve or shell has three
layers
▫ Thin outer layer to protect
against acidity of sea water
▫ Thick middle layer of CaCO3
▫ Inner layer has “mother of
pearl” coating to create a
smooth surface for the soft
body
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Class Bivalvia con’t.
• Typically sessile
▫ Use their foot as an anchor
▫ Fill it with hemolymph to
create a hatchet shape
▫ Contract foot and pull
themselves into the sand
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Class Bivalvia con’t.
•
•
•
•
Filter feeders
No radula
No distinct head
Nervous system has three
ganglia pairs
▫
▫
▫
▫
Mouth
Digestive system
Foot
All are connected
• Respond to chemicals and
touch
• Some have eyes along
mantle—calico scallop
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Clams
• Live buried in mud or sand
• Mantle cavity is sealed except
for the siphons
▫ Cilia generate current to pull
water in
▫ Water exits through
excurrent siphon
• Gills capture organic matter in
mucous
• Gills are also used for gas
exchange with hemolymph
• Typically separate sexes
• Marine clams use external
fertilization
• Freshwater clams use internal
fertilization
▫ Sperm in incurrent siphon
▫ Larvae exit the excurrent
siphon
▫ Eventually settle on bottom
and mature
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Oysters
• Make permanent attachment
to hard surface early in life
• Commercially grown for food
and pearls
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Scallops
• Motile
• Use shells in a clapping
motion to swim
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Teredo or Shipworm
• Not a filter feeder
• Bores into driftwood or boat
timbers and ingests the
particles
• Wood is broken down by
symbiotic bacteria
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Class Cephalopoda
• Name means “head foot”
• Octopuses, cuttlefish, squids,
chambered nautliluses
• Foot is concentrated in the
head, hence the name
• Free-swimming
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Class Cephalopoda con’t.
• Predatory lifestyle
• Circle of tentacles extending
from the head
• Jaws resembling a parrot’s
beak
• Advanced nervous system
▫ Largest brain of any
invertebrate
▫ Divided into lobes
▫ Millions of cells
▫ Capable of learning and
problem solving
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Class Cephalopoda con’t.
• Well developed senses
▫ Eyes can form images
▫ Tentacles have chemical
sensing ability
• Closed circulatory system
• Separate sexes
▫ Males have specialized
tentacles for sperm transfer
▫ Females lay and guard eggs
▫ No trochophore stage
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Squids
• Ten tentacles
• Two longest tentacles for prey
capture, other eight force food
into mouth
• Pump water through excurrent
siphon for propulsion
• Most grow to 1 ft long
• Giant squid grows to 60 ft
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Octopuses
• Eight tentacles
• Don’t chase prey like squid—
crawl and grab
• Seldom exceed 3 ft in diameter
• Pacific octopus can grow to 8
ft in diameter
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Chambered Nautilus
• Shell
• Series of gas-filled chambers
separated by partitions
• Confined to outermost
chamber
• Gas in the chambers allows
buoyancy
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Cuttlefish
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Phylum Annelida Characteristics
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•
•
•
Name means “little rings”
15,000 species
Bilaterally symmetrical
Most distinctive feature is the
rings
• True coelom
▫ Divided into compartments
by partitions
▫ Evolutionary advantage—
allows different parts to
expand and contract
independently
• Duplication of organ systems
in each segment—injury
insurance
• Setae and parapodia—allow
for division into three classes
▫ Oligochaeta
▫ Polychaeta
▫ Hirudinea
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Class Oligochaeta
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•
•
•
Name means “few bristles”
Live in soil or freshwater
No parapodia
Have a few setae on each
segment
• Most familiar class member is
the earthworm
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Class Polychaeta
•
•
•
•
•
•
•
•
2/3’s of annelids
Name means “many bristles”
Setae are found on parapodia
Antennae and specialized
mouth parts
Only annelids with
trochophore stage
Most are marine
Some are free-swimming
predators and use strong jaws
for feeding
Others feed on sediment
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Class Hirudinea
• 300 species
• Live in calm bodies of
freshwater or moist vegetation
on land
• No setae or parapodia
• Each end has a sucker
• Can crawl using suckers
• Can swim with undulating
motion
• Carnivorous
▫ Invertebrate prey
▫ Blood suckers
▫ Secrete anesthetic and
anticoagulant
▫ Can ingest 10x their weight
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Earthworm Structure and Movement
• More than 100 segments
• Circular and longitudinal
muscles
• Movement
▫ Anchor posterior setae
▫ Contract circular muscles to
extend
▫ Anchor anterior setae
▫ Contract longitudinal muscles
to pull forward
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Earthworm Feeding and Digestion
• Ingest soil while burrowing—
use muscular pharynx
• Soil moves into the crop—
temporary storage area
• Soil is moved from crop to
gizzard—a muscular gut that
grinds the soil to release the
nutrients
• Nutrients are absorbed by the
intestine—typhlosole folds
• Undigested materials exit
through anus
• Maintains soils fertility by
decomposition and aeration
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Earthworm Circulation
• Closed system
• Blood travels to the posterior
through a ventral blood vessel
• Blood returns to the anterior
heart through a dorsal blood
vessel
• Aortic arches link the vessels—
these arches act as hearts to
contract and move the blood
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Earthworm Respiration and Excretion
• Gases are exchanged by
diffusion through skin and
cuticle—no specialized organs
• Diffusion only occurs if skin is
moist—mucous and cuticle aid
in this effort
• Cell wastes are eliminated
through nephridia
▫ Each segment, except, the
first three, and last one, have
nephridia
▫ Coelomic fluid passes
through, water is reabsorbed,
wastes eliminated
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Earthworm Nervous System
• Chain of ganglia connected by
a ventral nerve cord
• Most segments contain a
ganglion
• Nerves branch from ganglia
• Several anterior ganglia are
fused to form a brain
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▫
▫
▫
▫
▫
Light
Touch
Chemicals
Moisture
Temperature
Vibration
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Earthworm Reproduction
• Hermaphrodites that do not
self-fertilize
• Mating
▫ Press ventral surfaces together
▫ Anterior ends are pointed in
opposite directions
▫ Held together by mucous and
setae at the clitellum
▫ Sperm is injected and moves to
seminal receptacle
▫ Each worm then secretes a
tube of mucous and chitin
where sperm and eggs meet
outside the body
• 2-3 week development prior to
hatching
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