Transcript Molluscs(2011)

Molluscs: What are they?
Definition: Soft-bodied animals that
have an internal or external shell
at some point in their development
Molluscus means 'soft' in Latin
evolved 600 MYA
100,000 + species
7 classes
size: grain of sand
to 20m long
Molluscs
– Characteristics that Unify
Have true coelom
Are protostomes
Have trochophore
larvae
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Trochophore larvae
Swim in open water
Feed on tiny floating
plants
Also seen in
annelids
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Common
ancestor
Tuft of Cilia
Ring of Cilia
Protostomes, Coelomates
Molluscs
– Characteristics that Unify
Have foot, mantle,
visceral mass, shell
Some lack shells,
but evolved from
shelled ancestors
Variations on same
basic body plan
used to group into
classes
Mollusk form: Visceral Mass
Contains
internal
organs
Just below
mantle
Mollusk form: Mantle
Thin tissue
layer covering
most of a
mollusc's
body
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Usually
covers
visceral mass
Usually
secretes shell
Mollusk form: Shell
Found in most
molluscs
Secreted by mantle
Made of Calcium
carbonate (CaCO3)
Snail shell
Whelk Shell
Abalone shell
Necklace made
from Abalone
Shell
Mollusk form: Foot
Soft and muscular
Usually contains mouth and other
structures associated with feeding
Adapted - Flat to crawl
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Spade-shaped to burrow
Tentacled to capture prey
Molluscs –
classified by the
modifications of the Foot
Class Gastropoda
Gastropods –
“stomach foot”
Foot is broad and
muscular
found along the
ventral surface
used for moving,
eating
Examples: Snails,
slugs, nudibranchs
Class
Gastropoda
- Snails
Gastropods - Sea
slugs/nudibranchs
Class Cephalopoda
the tentacled molluscs
“Head –foot”
Foot is modified into
head with tentacles
coming out of it
Have very little shell if
any
Cephalopods include:
Octopi
Squid
Cuttlefish
Nautiluses
May have internal shell
Swim with jet propulsion
Squid – 8 arms + 2 long
tentacles
Class Bivalvia
Have 2 shells – foot
can extend out of
shell
Clams
Oysters
Mussels
Geoduck, or king clam. A
delicacy! Yumm Yumm
Mollusk: Feeding
Many forms of feeding: herbivores, carnivores,
filter feeders, detritus feeders and parasites
Feeding
Many molluscs have
a structure that is
like a very rough
tongue – has
hundreds of tiny
teeth for grinding
through shells or
scraping algae off of
rocks
Feeding
Radula: tongue shaped structure made of
flexible skin with hundreds of tiny teeth, like
sandpaper
 Stiff supporting rod of cartilage
 Scrapes over surface
 Predators use to drill holes in animals
Cartilage Rod
Radula in grey
Magnified 50x
Mollusk: Feeding cont'd
Some carnivorous mollusks use sharp jaws
instead
Filter feeding mollusks (bivalves) use gills to sift
food from water
 Phytoplankton get stuck in sticky mucus
 Cilia pass into mouth
Mollusk: Feeding cont'd
A Squid's beak-used
to kill and dismember
prey.
Molluscs – Filter feeders
They also
use the
gills to
BREATHE
Clam – How it eats
Incurrent siphon
pulls water across
gills
Food particles stick
to gills
Coordinated cilia
move food to mouth
Food is
stored/digested in
stomach and
intestines
Solid wastes exit via
the anus
Mollusk: Respiration
Usually by gills
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Aquatic: inside
mantle
Exception:
nudibranchs
Exception - Nudibranchs
Means “naked gill”
b/c gills are exposed
Nudibranchs
3000+ species
Carnivorous
6 mm – 31 cm
Hermaphrodites
Avg life: up to 1 year
Some solarpowered!
Store algae and live
off sugars
Nudibranchs
Respiration
Land snails and slugs use a moist sac inside
the mantle
Sac’s lining is convoluted (to increase surface
area) and lined with blood vessels
Mollusc: Internal Transport
Open circulatory system: blood pumped
by simple heart through body tissue in open
spaces called sinuses (not contained in blood
vessels)
Sinuses lead to vessels that pass through gills
where gas exchange occurs
Works well for slow-moving (sessile)
organisms like slugs, snails and clams, but
inefficient for faster or larger molluscs
Internal Transport
Closed circulatory system: blood always
moves inside vessels
Good for fast moving molluscs such as squids
and octopi (hunters)
Closed circulatory system
Open circulatory system
Circulatory System
Comparisons
Molluscs: Excretion
Solid waste excreted via
anus as feces
Nitrogen-containing
waste, such as
ammonia, removed by
tube-shaped organs
called nephridia
Nephridia remove
ammonia from blood
and release it to outside
environment
Mollusc: Response
Nervous system complexity highly varied
Two-shelled molluscs usually simple nervous
systems (they just dig in sand)
 Small ganglia near mouth, a few nerve
cords, simple sense organs, statocysts
(organ for balance) and ocelli (eye spots)
Clam burrowing in sand
Statocyst
Swimming scallop
Scallops
Eye spots allow for
detection of
predators
Sustainably
harvested in BC as
food source
Only migratory
bivalve
Mollusc: Response
Tentacled, fast moving molluscs highly
developed nervous systems (to hunt)
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Well developed brain; capable of memory;
complex sense organs
Octopi:
Well-developed
brain (with
memory)
Eyes that are
similar to ours –
form images
Octopi
Highly intelligent
Short and long-term
memory
Die soon after
mating
3 hearts
Can crawl, swim, jet
propulsion, walk
Some camouflaged
Mollusc: Reproduction
Usually separate sexes with external fertilization
(snails, most two-shelled mollusks)
 Release egg + sperm into open water in large
amount
 They meet by chance, developing into freeswimming trochophore larvae
In tentacled mollusks and some snails,
fertilization occurs inside female
Fertilization also internal in hermaphrodites
Reproduction
Oysters –
hermaphrodites that
change sexes each
season – sometimes
they are the males,
sometimes the
females.
Defence Mechanisms - Gastropods
Slugs hide under rocks
or only come out at
night
Some gastropods are
poisonous – brightly
colored to warn off
predators
Some nudibranchs save
the nematocysts from
the cnidarians they ate,
and sting their predators
with them
Defence Mechanisms- Cephaloods
Octopi move
rapidly
backwards with
their jet
propulsion of
water
Some release
foul-tasting
black ink
Some can
change colours
Read text p. 593 (How Mollusks Fit Into Our
World)
Mollusks in our world: Positives
Roles: eat plants,
prey on animals,
clean up surrounding,
eat detritus, host
symbionts or
parasites, are
parasites
Important food
sources, sometimes
to humans
Mollusks in our world: Positives
Concentrate
dangerous pollutants
 Monitor levels of
toxins
Environmental “Watchdogs”
Filter feeders remove
the pollutants from
the water and
concentrate them in
their bodies
Environmentalists can
use these animals to
learn information
about levels of
pollution in the water.
Don’t eat bivalves during a
RED TIDE
What is red tide?
Red Tide
Mollusks in our world: Positives
Snails never develop cancer
 how?
Teeth of Mollusc: Dental use (toughened
with iron biominerals- harder than steel)
 Stronger, more flexible, resistant to
fracture
 Waterproof strong adhesive
Mollusks in our world: Negatives
Damage crops
Shipworms eat
hulls
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Termites of the sea
Problem as food
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Eating
concentrated
pollutants
Red tide
Poisonous !