Mollusks and Echinoderms
What is a mollusk?
Mollusks are invertebrates with soft bodies that
are often protected by a hard shell (oysters,
clams, snails).
Some lack the shell
All mollusks have a thin layer of tissue that
covers their internal organs called the mantle.
Found everywhere.
Other Structure
Mollusks have bilateral symmetry.
Internal organs include kidneys: What are they
used for?
Many mollusks also have a structure called the
radula: a flexible ribbon of teeth. This structure is
used to scrape food off of objects.
Snail radula
History
Mollusks have been around for millions of years.
We know this because their hard shells form
very nice fossils.
Also form Limestone.
What are fossils?
Limestone
Biological sedimentary rock—formed from shells
of organisms (mollusks) over many years.
Different names of limestone based on how rock
is formed, its appearance or composition.
Limestone is rock by definition that contains at
least 50% calcium carbonate.
Types of Limestone
Coquina: A poorly-cemented limestone that is composed
mainly of broken shell debris. It often forms on beaches
where wave action segregates shell fragments of similar size.
Other types of limestone
Chalk: A soft limestone with a very fine texture that is usually white
or light gray in color. It is formed mainly from the calcareous shell
remains of microscopic marine organisms such as foraminifers or the
calcareous remains from numerous types of marine algae.
Limestone rock
Tufa: A limestone produced by
precipitation of calcium-laden waters at a
hot spring, lake shore or other location.
Coral reef forming limestone from
calcium carbonate skeletons
Limestone- Forming Environment
Nasa
satellite
image
100mi
wide
Stomach Foot
The largest group of
mollusks are the snails
and their relatives
(gastropods).
Get their name from the
fact their stomach and
foot are in the same
area.
Continue
Live everywhere from the ocean to treetops.
Can be herbivores, scavengers and carnivores
(cone shell).
Many snails have a tight fitting trap door on their
shell that they can close off if threatened.
Slugs have the same features as snails except
one.
Gastropods
Snails
Slugs
Two Shelled Mollusks
Have two shells held
together by a hinge and
muscle.
Lack radula
Are filter feeders - use their
gills to catch food as they
breathe.
Food sticks to mucus on the
gills; then cilia take it to the
stomach.
Bivalves
Bivalves have three layers in their shell. The
inside layer has a pearly appearance.
As adults typically stay in one place.
Clams and scallops however can actively move
if startled
– Clams use their foot if startled to bury themselves.
– Scallops can clap their shells to leap away.
Bivalves
Sea Scallop
Giant Clam
Anatomy of an Oyster
Clams
Greater European Peaclam
Asian Clam
Mussels
How are Pearls Formed?
Pearls are formed when a sand grain or parasitic
worm gets caught in a bivalve. The mantle
becomes irritated and produces the pearly layer
over the irritation. This just makes it bigger and
more irritating. It keeps putting on layer after
layer forming a pearl.
Pearls
Natural pearls vary in size
and shape. Their shape
depends on the piece being
coated. These are rare and
very expensive.
Cultured pearls are formed
when the shells are opened
and different shape beads are
inserted.
Natural Black Pearl
Formation of a Pearl
Head Foots
Cephalopods means “headfooted”.
Foot is adapted as tentacles
around the mouth.
Some members of this group
are the octopus, cuttlefish,
and squid.
Most advanced of all
invertebrates.
Octopus
Found only in the ocean where they move by jet
propulsion.
Communicate by changing the color and
patterns of their skin.
Use their tentacles and suckers to capture food.
Excellent vision and nervous system.
They have even been found to remember things
they have learned in captivity.
Why does
this use a
bright
coloring?
Blue-ringed
octopus. One of the
most toxic animals.
Squid
Giant Pacific Squid
Cuttlefish
http://www.uwlax.edu/biology/Zoo-Lab/Lab-06/Index-Lab-6.htm
The Echinoderms
Spiny Skinned animals
Have radial symmetry (?)
Invertebrates that live in the ocean.
Have an endoskeleton that is made up of
calcium plates: Where would we find an
endoskeleton?
Symmetry is based on fives
Also have a water vascular system
Sea Stars or Starfish
Dissected starfish. Notice the radial canals which are
part of the water-vascular system.
Brittle Star
Sea Lily
Sea Lily or Feather star
Sea Urchin
Sand dollar
Sand dollars
Arrowhead
Flat Round
Sea Biscut
Pancake
Sea Gopher
Sea Cucumber
Water vascular system
Parts of the tubes can contract and squeeze the
water into tube feet. This allows the feet to grip
the surface underneath the organism, allowing it
to move.
They also use these tube feet to pull open the
shells of mollusks
Water-Vascular System
Tube feet
Sea Star
When feeding, a sea star grasps a bivalve (?) with all of
its feet and pulls the shell open.
Once the shell is open the sea star forces its stomach
out of its body and into the clam, and digests it
externally.
What other two organisms have we seen do this?
Can regenerate lost arms. Some species lost arms can
grow new bodies!!
Other Echinoderms
Brittle stars are close relatives to sea stars. Except their
arms are extremely long, slender, and flexible.
Sea urchins and sand dollars lack arms, but have hard
spines.
These spines are mobile and are used for movement.
Have teeth that they use to scrape food off of objects.
Continued
Sea cucumber bodies are soft and flexible.
Some have tube feet on their underbelly for
which they use to move across the sea floor.
They crawl along the sea floor sucking in food
found in the sand.
Other sea cucumbers are filter feeders that use
their tube feet to catch food particles in the
water.
Review
What type of symmetry do mollusks and echinoderms
have?
Who are the three groups of mollusks?
What is a radula?
What organ system do they have that the worms
lacked?
What happens if you cut an arm off of a star fish?
How does the water vascular system work?