CHAPTER 14
Mollusks,
Annelids,
Arthropods,
and
Echinoderms
Mrs. Nell’s 7th Grade Life Science Class
Kingdom- Animalia
Phylum- Mollusca
Mollusks
Mollusks are the soft-bodied invertebrates
in the phylum Mollusca. Mollusks usually
have shells (not the slug, though) and
bilateral symmetry.
The Body of a Mollusk
Mollusks have a soft
body covered by a
mantle (a thin layer of
tissue that makes the
shell or protects the
body if the mollusk
doesn’t have a shell).
Mollusk Gills
Mollusks have gills to exchange oxygen and CO2 with the
water.
gills
Visceral Mass
The body organs are located together in
what is called the visceral mass.
Mollusk Foot
Mollusks have a muscular foot for movement.
Circulatory System
Mollusks have an open circulatory system
(blood isn’t contained in vessels- blood
bathes the mollusk’s organs).
Classifying Mollusks
There are three main classes of mollusks:
1) Gastropods
2) Bivalves
3) Cephalopods
Gastropods
Gastropods or univalves are the largest class of
mollusks. Except for slugs, each has a single shell.
Members of the gastropod class are:
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Snails
Slugs
Abalones
Whelks
Sea slugs
Conches
Nutrition
Gastropods feed on
plant material using
their radula (a tongue
like organ with rows
of teeth that works
like a file).
Bivalves
Bivalves are mollusks with a two-part shell joined by a
hinge. Bivalves use siphons to filter feed. Some
bivalves are:
• Clams
• Oysters
• Scallops
Bivalve Defense
To protect themselves, clams will
borrow deep into the sand with
their muscular foot. Mussels and
oysters will cement themselves to
a surface. Scallops will open and
close their shell rapidly to move
away quickly.
Cephalopods
Cephalopods have a large, well-developed head. They have
tentacles with strong suckers for capturing prey. They have a well
developed nervous system and large eyes. Cephalopods have
closed circulatory systems, unlike other mollusks.
Some cephalopods are:
• Squid
• Octopus
• Chambered nautilus
Jet Propulsion
Cephalopods move by pushing water out
through an opening in their head. This jet
of water sends it backward. A squid can
move more than 60m/s this way.
Squid Internal Anatomy
Importance of Mollusks (I)
Mollusks provide food for fish, sea stars,
birds, and other organisms.
Importance of Mollusks (II)
Some invertebrates, like the hermit crab,
use empty mollusk shells as shelter.
Importance of Mollusks (III)
Clams, oysters, snails, and scallops are used
for food.
Importance of Mollusks (IV)
Pearls are produced by many species of
mollusks.
Kingdom- Animalia
Phylum- Annelida
Segmented Worms
Segmented worms belong to the Phylum
Annelida. Annelid means “little rings” and
describes the segments that makeup the
body of these worms. Some members of
the annelid phylum are…
• Earthworm
• Leeches
• Marine Worms
Segmented Worms & Mollusks
Like mollusks, all segmented worms have
a body cavity that holds their organs.
Setae
On the outside of each segment, annelids
have little bristle-like structures called
setae that help them move. Segmented
worms also use the setae to help them
stay in the soil if a bird gets a hold of them!
Earthworms
Earthworms eat soil. They use their crop for storage and their
gizzard to grind the soil. Digested food moves to the intestine
where it is broken down and absorbed by the blood. Undigested soil
and waste leave the worm through the anus.
Leeches
Leeches feed on the blood of
animals- including humans.
They have two suckers that they
use to attach to the animal. It
will then cut into the flesh and
suck out blood. Leeches
produce an anesthetic so that
the animal doesn’t feel the bite.
For centuries leeches were used
for blood letting because of the
mistaken belief that bodily
disorders and fevers were
caused by an excess of blood.
Today leeches are used to keep
blood flowing to reattach body
parts.
The "medicinal leech" feeding on blood from a human arm.
Marine Worms
Marine worms also have segments with setae. Some
marine worms trap food in tentacles. Others build tubes
to hide in.
Annelids & Mollusks- related?
Scientists think segmented worms and mollusks share a common
ancestor. They were the first of the animal groups to have bodies
with space for the body organs, and they both have a larva stage
early in their development.
Kingdom- Animalia
Phylum- Arthropoda
ARTHROPODS
Arthropods make up the largest phylum of animals
in the animal kingdom. Members of the arthropod
phylum include…
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Insects
Arachnids
Centipedes
Millipedes
Crustaceans
Molting Caterpillar
The Body of an Arthropod
Arthropoda means
“jointed foot” and
describes the jointed
appendages of
arthropods. The
appendages on an
arthropod include legs
antennae, claws, and
pinchers.
Arthropods and segmented worms- related?
The bodies of arthropods are divided into segments like those of
segmented worms so scientists hypothesize they may have a
common ancestor.
Exoskeletons
All arthropods have an external
covering called the exoskeleton that
protects the body. It is made of protein
and a carbohydrate called chitin. Once
the arthropod outgrows its shell it will
molt.
Kingdom- Animalia
Phylum- Arthropoda
Class- Insecta
Insects
Insects have three body regions: a head, thorax, and an abdomen.
The head has a pair of antennae, eyes, and a mouth. The thorax
has three pairs of jointed legs and sometimes wings. The abdomen
doesn’t have wings or legs attached.
The Body of an Insect
Insects have open circulatory systems. For their
respiratory system they have openings called spiracles
on the abdomen and thorax through which air enters and
waste gases are expelled.
Metamorphosis
Many species of insects go through a series of changes
called metamorphosis. Most insects (butterflies, beetles,
ants, bees, moths, flies…) develop through complete
metamorphosis. There are four stages of development:
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Egg
Larva
Pupa
Adult
Incomplete Metamorphosis
Grasshoppers,
silverfish, lice, and
crickets develop
through incomplete
metamorphosis. The
three stages of
development are
egg, nymph (a small
adult without wings),
and adult.
Kingdom- Animalia
Phylum- Arthropoda
Class- Arachnida
Arachnids
Arachnids are arthropods
with only two body regions
(the cephalothorax and
abdomen). They have
four pairs of legs but no
antennae. Arachnids
have 8 legs and poison
glands, stingers, or fangs.
Some arachnids are:
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Spiders
Scorpions
Mites
Ticks
Kingdom- Animalia
Phylum- Arthropoda
Class- Chilopoda/Diplopoda
Centipedes & Millipedes
Centipedes have one pair
of jointed legs per
segment. Millipedes
have two per segment.
Centipedes have a pair of
poison claws to inject
venom into their prey
(they eat snails, slugs,
and worms). Millipedes
feed on plants.
Kingdom- Animalia
Phylum- Arthropoda
Class- Crustacea
Crustaceans
Crustaceans are arthropods that have one or two antennae
and jaws called mandibles for crushing food. They have five
pairs of legs. The claws are for catching and holding food.
The other four pairs are walking legs. Some members of the
class Crustacea are:
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Crabs
Crayfish
Lobsters
Shrimp
Barnacles
Pill bugs
Water fleas
Blue Crabs
A male crab, or "Jimmy", has a long
narrow, inverted "T" shaped abdomen and
has blue tipped claws.
A female crab can be easily
identified by the shape of
her abdomen.
Abdomen of immature female crab
Abdomen of mature female crab
“Jimmy”
Some watermen say
that a male blue crab
looks like it has the
Washington
Monument on his
belly!
“Sally”
An immature female,
called "she-crab" or
"Sally," has an
inverted "V" (or
triangular) shaped
abdomen.
“Sook”
An adult female, called a
"sook," has an inverted
"U" (dome) shaped
abdomen. Some
watermen say that a sook
has the U.S. Capitol
Building on her belly!
Another easy way to tell
a male from a female is
that all female crabs
"paint their fingernails"
(have red tipped claws)males do not.
Pesticides and Insects
Most insects are harmless,
but farmers who are
concerned about crop yields
often use pesticides
(chemicals that kill
undesirable plants and
insects).
For Pesticide Use
• Farmers can produce more
food
• New ways of applying
pesticides may reduce amount
needed and ensure it affects
only the insect pests
Against Pesticide Use
• Kill not only intended pest but other organisms as well
• Pesticides accumulate in body tissues of organisms
• Environmental impact is too great
Kingdom- Animalia
Phylum- Echinodermata
Echinoderms
Echinoderms are spiny skinned invertebrates that live on
the ocean bottom. They include:
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Sea stars
Brittle stars
Sea urchins
Sand dollars
Sea cucumbers
Water-Vascular System
Sea stars have a water-vascular system (a network of
water-filled canals) which attach to thousands of tube
feet (‘suction cups’ that help the sea star feed/move).
Sea Stars
The sea star turns its
stomach inside out
and pushes it through
its mouth to eat. It
then secretes enzymes
that digest the animal.
When the meal is over,
the sea star pulls its
stomach back in.
The Sea Cucumber
Sea cucumbers
have soft-bodies
and tentacles
around their mouth.
When threatened
sea cucumbers may
expel their internal
organs and simply
regenerate them in
a few weeks!
This sea cucumber is eviscerating a portion
of its intestines to thwart an attack.
Importance of Echinoderms
• Providing information about how body parts regenerate
• Feed on dead organisms in the marine environment
Echinoderms Similar to Chordates
Of invertebrates- most similar to chordates
(mammals, birds, reptiles, amphibians, and fish)
– Complex body systems
– Embryo develops similar to chordates