Transcript Phylum Mollusca

Phylum Mollusca
Ch. 12
General Ideas
Phylum Mollusca
• Members are called Mollusks
• Example Species:
– Slug
– Squid
– Scallops
– Octopus
– Snails
Phylum Mollusca Characteristics
• Over 100,000 Species
• Many are marine, some are freshwater, and some live in
moist land environments
• Body in two parts:
– Head-foot
– Visceral mass
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Bilateral Symmetry
Radula (for feeding)
Mantle that secretes a calcareous shell
Small coelom for heart, nephridia, and gonads
Trochophore larvae produced (Protostome characteristics)
Open circulatory system in all except cephalopods
May have been the first animals in the course of evolution to
have a coelom
Important Mollusk Body Parts
• Look at the Picture on Page 182
• Mantle
– Attaches to the visceral mass, enfolds most of the body, and
may secrete a shell that overlies the mantle
• Radula
– Tongue-like organ with rows of teeth found in the mouth used to
scrape food into their mouths
• Mantle Cavity
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Found between the mantle and the foot
Room for organs
Gas exchange
Excretion
Elimination of wastes
Release of gametes (reproduction)
Feeding and Digestion
• Mollusks have complete guts with
digestive glands, stomachs, and
intestines.
• The digestive system has 2 openings-a
mouth and an anus.
• Radula
– Can be used to scrape algae, drill holes in
shells, or tear up the food the capture
– Few mollusks do not have radulas, such as
clams who are filter feeders.
Respiration
• Most mollusks have respiratory structures
called gills
– Gills are parts of the mantle that consist of a
system of projections like fringes of a blanket.
– Gills contain a rich supply of blood for the
transport of oxygen to the blood and for the
removal of carbon dioxide from the blood.
– Gills also move water into and through the
mantle cavity in a continuous stream using
highly branched structures that increase
surface area through which gases can diffuse.
Circulation
Mollusks have a well-developed circulatory system that
even includes a chambered heart.
Open Circulatory System
Closed Circulatory System
• Most mollusks
• Blood is pumped out of vessels
into open spaces surrounding
body organs
• Enables animals to diffuse
oxygen and nutrients into
tissues that are bathed in
blood and also to move CO2
from tissues into the blood.
• Slow-moving mollusks, such
as snails and clams, utilize this
system because they do not
need rapid delivery of oxygen
and nutrients for quick
movement!
• Only some mollusks, such as
squid.
• Blood is confined to blood
vessels as it moves through
the body.
• Mollusks that move quickly,
such as octopi, need more
energy than slow-moving
mollusks, and the closed
circulatory system quickly
deliver nutrients and oxygen.
Excretion & Response to Stimuli
• Excretion:
– Most mollusks get rid of metabolic wastes through
nephridia (similar to annelida)
• Response to Stimuli:
– Have a nervous system that coordinates movement
and behavior.
– Mollusks that are more highly evolved, such as
octopuses, have a brain. In addition, octopuses
have complex eyes similar to human eyes with
irises, pupils, and retinas. BUT, most mollusks only
have simple structures in the eyes that reflect light.
Movement
• Mollusks can move many
different ways:
– Muscular foot of a clam enables it
to burrow into wet sand
– Mollusks with 2 shells can clap their
shells together for short bursts of
rapid swimming.
– Most slugs and snails creep along
moist areas on a slime trail of
mucus secreted by glands in the
foot.
– Octopi and squid take water into the
mantle cavity and expel it through a
tube called a siphon.
Reproduction
• Mollusks generally reproduce sexually by
releasing their eggs and sperm into the
water at the same time where fertilization
occurs externally….but there are a few
exceptions:
– A few bivalves and gastropods that live on
land are hermaphrodites and fertilization
occurs internally.
– Copulation can occur through mutual sperm
transfer (think annelid) or even where one is
male and one is female (more rare)
Taxonomy of Mollusca
• Kingdom Animalia
– Phylum Mollusca
• Class Caudofoveata
• Class Aplacophora
• Class Polyplacophora
• Class Monoplacophora
• Class Scaphopoda
• Class Bivalvia
• Class Gastropoda
• Class Cephalopoda
Class Bivalvia
• 30,000 species (2nd larges molluscan class)
• Filter-feeders (also remove bacteria from
polluted water) DO NOT EAT BIVALVES
FROM POLLUTED WATER!
• No head or radula, but do have wedge-shaped
foot
• Marine and Freshwater
• Two shells called valves
• Umbo – oldest part of the shell
• Example species: Clams, oysters, mussels, &
scallops
Clam
Giant Clam Life Cycle
Oysters
"There once was an oyster
Whose story I tell,
Who found that some sand
Had got into his shell.
Now the years have rolled around,
As the years always do,
And he came to his ultimate
Destiny - stew.
It was only a grain,
but it gave him great pain.
For oysters have feelings
Although they're so plain.
And the small grain of sand
That had bothered him so
Was a beautiful pearl
All richly aglow.
Now, did he berate
the harsh workings of fate
That had brought him
To such a deplorable state?
Now the tale has a moral,
for isn't it grand
What an oyster can do
With a morsel of sand?
Did he curse at the government,
Cry for election,
And claim that the sea should
Have given him protection?
What couldn't we do
If we'd only begin
With some of the things
That get under our skin.”
'No,' he said to himself
As he lay on a shell,
Since I cannot remove it,
I shall try to improve it.
- Unknown
Pearls being removed from oysters
Read, Write, Talk
• Pick up the “Pearls” article and read it
• Write on your paper interesting facts or
something you do not understand
• Last we will discuss, expect me to ask you
questions!
Akoya Pearl
Scallops
Scallop
Mussels
Mussel Anatomy
Mussel
Non-native zebra mussels
encrusting a native mussel from the
Ohio river
Zebra Mussel – Nuisance Species
http://fl.biology.usgs.gov/Nonindigenous_S
pecies/ZM_Progression/zm_progression.ht
ml
Zebra Mussel 3, 2, 1
• Read
• Write:
– 3 most important facts
– 2 questions you have
– 1 connection (something you already know)
Mother of Pearl
buttons from
mussel shells
Class Gastropoda
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Marine, freshwater, & terrestrial
Over 35,000 species
Shell if present is coiled
Torsion – 180o counterclockwise twisting of
viseral mass, mantle, & mantle cavity
One broad foot for creeping
Uses a Radula (rough tongue) to eat
1 Shell (except nudibranchs and slugs)
Definite Head, Eyes and Tentacles
Example species:
– Snails, Limpets, Slugs, Nudibranches
Snails
Limpets
Slugs
Nudibranch
Class Polyplacophora
• Chitons!
• Have a reduced head, a flattened foot, and
a shell that divides into 8 overlapping shell
plates!
• Most live near edge of marine waters
(intertidal zone) and feed on algae
• About 1,000 species
Chiton
Class Cephalopoda
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Foot modified into a circle of tentacles and a siphon
Most complex mollusks (and possible invertebrates)!
Shell reduced or absent
Marine
Well developed head and brain
Human-like eyes
Uses a beak, a radula,
and tentacles to eat
• Less than 1,000 species
• Well defined head
• Example Species:
– Octopuses, squid, cuttlefish, and nautiluses
Octopus
Squid
Cuttlefish
Nautilus