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Chapter 29 – Mollusks, Segmented
Worms and Starfish ( Sea Stars)
Snails, Earthworms and Starfish
What is a Mollusk?
Clam,squid, snail…….octopus
. Soft
bodies …and a shell
2. Bilateral symmetry
3. A coelom ( a true body cavity)
4. A muscular foot , mantle and
visceral Mass
5. Two body openings
(mouth and anus)
6. Swimming, ciliated larva
7.) All but bi-valves have a radula
(tongue-like organ) to take in food with
Three classes of Mollusks
–1. Bivalves - two shells
– a hatchet-like foot
2. Gastropoda- Those
one shell (usually
spiral) and slide on
their foot.
 3. Cephalopoda – no
shell tentacles and
well developed
nervous systems.
Body systems of a Mollusk
Have a true coelom which contains organs for
digestion, like the radula, esophagus,
stomach and intestines.
Many mollusks use gills to extract oxygen
from the environment (almost 50%), while
others use moist skin.
Excretion is done using a nephridia, which will
also recover molecules needed to remain in
the body (sugar, salt, water)
Body Systems continued
Many mollusks have a three chambered
heart that pump blood to an open
circulatory system. Blood is sprayed over
vital organs for diffusion of nutrients.
Octopuses and squid are the exception
with both having a closed system to allow
for the speed and endurance both
Hermaphrodites exist within the phylum
but most are sexual reproducing
Some oysters are able to change sex
over and over.
Where do mollusks live??
Mollusks live in a wide variety of
They live in polar regions and tropical
Some are free swimming, others
sessile, & some move across land.
A close look at Gastropods…
37,000 called the univalves…(one shell)
The largest class…. snails,
slugs, and sea slugs.
Herbivorous, using the radula
(a rasp-like tongue) to scrape
surfaces for food.
The body of the snail, called
the visceral mass, is found
within the shell.
Crawls on belly - (foot)
secretes mucus….
A close look at Gastropods…
sometimes called univalves
Open circulatory system
allows blood to flow
 2- pairs of antenna eyes
on long ones - smell for
Most land univalves are
 The abalone and conches
are examples of marine
Naked gastropods…the slugs
No shell, just a thick
layer of mucus coating
their bodies.
Some sea slugs called
nudibranchs feed on
jellyfish and incorporate
the nematocysts into
their own tissues!
Some sea slugs secrete
a poisonous mucus for
A closer look at BIVALVES
A large muscular foot
for burrowing in the
Bivalves are filter feeders.
Gills are coated with
mucus and cilia. They
trap food in the mucus.
The mantle secretes
the shell… and any
particle caught in
between the shell
and mantle is coated
to stop irritation.
Bi-Valves continued
Adductor muscles located on the
opposite side of the opening halves
cause great contractions and can even
help scallops travel from place to place.
Siphon tube, opposite the foot of a bivalve is a hollow tube to draw in water
and filter prey. ( No radula, so they
filter feed)
Cephalopods- Squid,
These are the most complex
Tentacles with suckers are used for
moving and capturing prey.
A sharp beak-like radula for ripping
apart the prey.
These species have a closed
circulatory system (most efficient).
The giant earthworm
of Australia can be 3m
Fan worms trap food
in the mucus of their
fan-like gills.
Leeches secrete
chemicals that are
used as anesthetics,
anti-clotting agents,
and to dilate blood
vessels to increase
blood flow.
Repeating segments that move
independent of each other.
Helps in the advanced movements of
Each segment has it’s own muscles
attached to help control movements
The annelids….segmented
(tiny rings)
worms !!
worms and leeches
These have a coelom and
two body openings.
Each segment has its
own muscles!
Each segments has a
kidney and a nerve
The Body System of the Annelids
The digestive
system is
complete with a
pharynx, crop,
gizzard, glands,
intestines, and anus.
The circulatory
system is closed and
has 5 aortic arches
that pump blood
Body Systems Continued
Excretion is performed by nephridia
With the addition of segmentation
comes specialization. Which means
stimuli must be stored and controlled by
a ganglion (Very simple brain)
Septa are the segments and nutrients
get to each by circulation and the
impulses come from the nerve cord.
Setae “Anchor” Away
Small hair like
projections stick out
of each septa to
anchor and aide in
motion. Movement
is also controlled by
muscle contractions.
Reproduction of Annelids
Although they are
annelids reproduce
with a partner every
time and they all get
Earthworms lock,
pass sperm to each
other, eggs get
Echinoderms = Sea Stars
( The starfish)
5 to many arms around a central disk
No blood!! Pump sea water thru body!
Eyespots on end of arms
External Digestion- stomach is thrown
up out of body!!
Eat Clams oysters and others!!
Internal skeleton- spines
Echinoderm Types
Sea Stars – starfish – 5 to 12 arms
Brittle stars – wire-like arms move
very fast
Sea Urchin – many spine-like arms
looks like a pin cushion
In all other blastula
organisms, the
mouth was the first
to develop, but now
it is second.
Chordates and
development in the
same way during
Body Systems to perform life
Water vascular
system is used for
gas exchange,
eating, and
Tube feet also help
in respiration,
excretion and
circulation ( no
Other characteristics..
Tubed feet that acts as suckers
Spiny external skeleton (ossicles)
Madreporite – filters sea water before it
enters animal!
Regenerate lost arms!
Sexual reproduction!
Importance of
Mollusks and Echinoderms….
Serve as food for many people.
Most eaten invertebrate type!
Pearls and other jewelry…
Snails destroy crops.. And serve as a
carrier for disease- causing parasites!
Starfish eats clams, oysters, and
Sea cucumbers are eaten in China!