CHAPTER 13 p. 360
Mollusks, Echinoderms, and Arthropods
Mollusks PHYLUM
MOLLUSCA
 means “soft”.
 second largest phylum.
 Ex. Snails, clams, squids
 all have bilateral symmetry.
SOME
LIVE
ON
LAND
MOST LIVE IN WATER
MOLLUSK BODY PLAN
FOUR BASIC PARTS
1) MANTLE
- creates the shell.
2) VISCERAL MASS
- internal organs.
3) SHELL
- for protection.
4) FOOT (or headfoot)
- for movement.
- most have an
open circulatory
system.
(the blood is not
contained in
vessels).
CLASSIFYING MOLLUSKS
1)Bivalves
- ex. clam, oyster,
scallops.
Class Bivalvia
“
“
- also known as
Class Pelycepoda
“
“
-have a two-part
shell linked by a
hinge.
- have a strong
muscular foot for
movement.
Bivalves are filter feeders.
MORE BIVALVES
Scallops
Oyster
Scallop
Giant Clam
Bivalve Body Plan
Gills
Visceral mass
Foot
Mantle
Shell
2) Univalves
“
Ex. snails, conches,
slugs.
- in Class Gastropoda
“
“
because they walk on
their stomach.
- have only one shell.
“
Univalves are the largest
class of mollusks.
Triton
Murex
Slug
Gastropods obtain food by scraping
material off ‘rocks’.
- they have a
tongue-like
organ called a
radula.
MORE GASTROPODS
Land Snails
Slug
Edible Snail
Conch
SNAILS
• Crawl on a layer of slime.
• Land snails breathe with lungs. Water
snails have gills
• Snails cannot hear.
• Snails are hermaphrodites.
• Most travel about 23 inches per hour!
3) CLASS CEPHALOPODA
• means “headfoot”.
• includes octopus
and squid.
Squid
Octopus
Cephalopods are
the most
complex class.
- have a closed
circulatory
system.
- their ‘foot’ is
their tentacles.
MOVEMENT: JET PROPULSION
CEPHALOPODS
Chambered Nautilus
- an “ancient”
cephalopod.
Octopus
- eight tentacles.
Squid
- ten tentacles
CEPHALOPOD FACTS
• A cepholopod eye is
somewhat similar to ours and
is the animal kingdom’s
largest.
• The Giant Squid is over 65
feet in length.
• Octopus swim ‘backwards’.
• Squid and octopus do not
have shells.
• Some can release an “ink” to
escape predators.
• Most have a “beak” which can
tear apart their prey.
Importance of Mollusks
1) Food
- clams, oysters,
snails, calamari,
octopus, etc.
2) Pearls
• Created by the mantle.
• It secretes nacre over
an irritant (like a grain of
sand).
• Nacre is also called
“mother of pearl”.
• It takes many layers of
nacre to make a pearl.
REVIEW THE THREE MAJOR CLASSES
<
CLASS GASTROPODA
CLASS BIVALVIA >
<
CLASS CEPHALOPODA
ECHINODERMS (p. 380)
Phylum Echinodermata
ex. starfish, sea
urchin
- have radial
symmetry.
‘
‘
- some seastars have the ability
to regenerate.
- starfish have tubefeet on their
tentacles which act like suction cups.
- for movement
and feeding.
Starfish can ‘extend’ their stomachs to
digest their prey.
More echinoderms
Crown of thorns seastar
Sea Cucumber
Pacific Seastar
Sand Dollar
ASSIGNMENT:
WORKSHEET “MOLLUSCA”
PHYLUM ARTHROPODA “
p. 370
- largest phylum of
animals - more
than all of the
other phylums put
together.
- an estimated 10
million species.
“
Arthropods are more complex.
- they have
respiratory
circulatory
nervous
systems.
- all have an open circulatory system.
Respiratory System
- water arthropods have “gills”.
- land arthropods have air sacs/trachea.
- air enters the book
lungs thru holes
called spiracles.
Arthropods can have several pairs of
appendages.
Ex. legs, wings,
pincers.
Their bodies have a hard outer
covering called an exoskeleton
The exoskeleton does not grow. It
must be molted or shed.
- the new
exoskelet
on is soft
and takes
time to
harden.
ARTHROPOD CLASSES
1) Class insecta
- largest class of
arthropods.
Ex. ants,
grasshoppers,
beetles, etc.
Insects have three
body regions.
- all have six
legs.
- the only class
able to fly.
Insects have a
compound eye
(many lenses)
and a pair of
antennae (to
sense)
Insects are classified into orders
according to its mouth parts
(or how it eats).
* chewing - grasshopper
* piercing - mosquito
* sucking - fly
ASSIGNMENT:
WORKSHEET
“CLASS INSECTA”
INSECT DEVELOPMENT
Metamorphosis (p.372)
- a change in form that an organism
goes thru to become an adult.
A) Complete
metamorphosis
Ex. butterfly
1) egg
2) larva
(caterpillar)
3) pupa
-inactive stage
- forms a
chrysalis
(cocoon)
4) Adult
Monarch larvae
Chrysalis
Complete Metamorphosis
B) Incomplete
metamorphosis
Ex. grasshopper
1) egg
2) nymph
- small adult
- no wings
- many molts
to
3) Adult
No real ‘change’ - it
just grows larger.
Which type of
metamorphosis?
Incomplete
Complete
2) Class Arachnae “Arachnids”
p. 374
Ex. spiders, ticks,
scorpions.
- have eight legs.
- no antennae.
Spiders have book lungs
- air moves over structures that look like
pages of an open book.
- openings are called _____.
Arachnids have two body parts.
1) cephalothorax
- head and chest
area.
2) abdomen
- internal organs
- arachnids have simple eyes
- they can sense light/dark but
cannot see images.
Arachnids have more appendages than
insects.
stingers
- at the end of the
abdomen.
Ex. scorpion
fangs
- inject poison - a
paralyzer.
- it also liquifies the
prey’s inner parts.
- the spider sucks it out.
spinnerets - are tubes which ‘spit out’
material make webs and capture food.
ASSIGNMENT:
WORKSHEET
“METAMORPHOSIS”
3) Class Myriapoda ‘myriapods’
“
p. 375
“
Centipede
- “hundred legged”
- many body
segments.
- eats other insects
- has poison fangs.
Millipede
- “thousand legged”
- many body
segments.
- eats dead plants.
- one pair of legs per
segment.
- can move only
one side at a time.
- ‘wriggle’.
- two pair of legs per
segment.
- can move both
sides at a time.
- smooth movement
- stink glands if
threatened.
- slower.
ASSIGNMENT:
WORKSHEET
‘ARTHROPODS’
4) Class Crustacea
Ex. crab, lobster,
shrimp
- similar
characteristics to
arachnids.
- two body parts
“Crustaceans”
p. 377
- but has many more appendages.
- two pair of antennae
to sense info about
their environment.
- claws
- used to capture
or hold prey.
- also the first pair
of legs.
- four pairs of walking
legs.
- five pairs of
swimmerets.
- uropod
- the fan shaped part of the tail.
- used for swimming.
- some can regenerate
appendages.
- have mandibles
- jaws for chewing.
- they also molt.
- have compound eyes usually
located on long stalks
- more than one
lense
- can see
movement
better.
- see over a
wider area.
-most live in water…
not pill bugs
- a huge source
of food for
people.
More crustaceans…
Crayfish
Blue Crab
Fiddler Crab
Shrimp
ASSIGNMENT:
WORKSHEET
“CRUSTACEANS”
What are these structures?
3.
2.
1.