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Chapter 15
Invertebrates
Table of Contents
Section 1 Simple Invertebrates
Section 2 Mollusks and Annelid Worms
Section 3 Arthropods
Section 4 Echinoderms
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Chapter 15
Section 1 Simple Invertebrates
Objectives
• Describe the body plans, nervous systems, and
guts of invertebrates.
• Explain how sponges get food.
• Describe three cnidarian characteristics.
• Describe the three kinds of flatworms.
• Describe the body of a roundworm.
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Chapter 15
Section 1 Simple Invertebrates
Invertebrate Characteristics
• An Invertebrate *
• About 96% of all animal species are invertebrates
• Invertebrates have three basic body plans, or *
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Chapter 15
Section 1 Simple Invertebrates
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Chapter 15
Section 1 Simple Invertebrates
Invertebrate Characteristics, continued
• Nerves *.
• Nerves allow animals to sense their environment
and control their actions.
• Some invertebrates have ganglia. A ganglion is a
concentrated mass of nerve cells.
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Section 1 Simple Invertebrates
Invertebrate Characteristics, continued
• Guts Almost all animals digest food in a gut. A gut is
a*
• Complex organisms have a coelom. A coelom is a *
• Other organs can also be found in the coelom, but
they are separated from the gut.
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Chapter 15
Section 1 Simple Invertebrates
Sponges
• Sponges are the simplest invertebrates. They are
asymmetrical and have no tissues, gut, or nerves.
• How Do Sponges Eat? A sponge sweeps water
into its body through its pores. Pores are *
• Collar cells *
• * called the osculum.
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Chapter 15
Section 1 Simple Invertebrates
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Chapter 15
Section 1 Simple Invertebrates
Sponges, continued
• Body Part Abilities Sponges have some unique
abilities.
• If you forced a sponge’s body through a strainer, the
separated cells could come back together and reform
the same sponge.
• If a part of a sponge is broken off, the missing part
can *
• Sponges are the only animals that can use
regeneration as a form of reproduction.
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Section 1 Simple Invertebrates
Sponges, continued
• Kinds of Sponges All sponges live in water, and
most live in the ocean. Sponges come in many
different shapes and sizes.
• Most sponges have a skeleton made of hard fibers
called spicules. Some spicules are *.
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Chapter 15
Section 1 Simple Invertebrates
Cnidarians
• Cnidarians are more complex than sponges.
Cnidarians have complex tissues, a gut, and a
simple nerve network.
• Two Body Forms A cnidarian body can either be in
medusa form or polyp form. Medusas swim *
• Both the medusa and the polyp forms have radial
symmetry.
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Chapter 15
Section 1 Simple Invertebrates
Body Form of Cnidarians
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Chapter 15
Section 1 Simple Invertebrates
Cnidarians
• Stinging Cells All cnidarians have tentacles
covered with stinging cells. Cnidarians use their
stinging cells *
• Kinds of Cnidarians There are three major
classes of cnidarians: *
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Chapter 15
Section 1 Simple Invertebrates
Flatworms
• Flat worms have bilateral symmetry, a clearly defined
head and two large eyespots.
• The eyespots cannot focus, but the flatworm can use
them to sense the direction that light is coming from.
•Some flatworms also have sensory lobes that are used
for detecting food.
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Section 1 Simple Invertebrates
Flatworms, continued
• Planarians Planarians live in freshwater lakes and
streams or on land in damp places. Most planarians are
predators.
• Flukes Flukes are parasites. A parasite is *
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Chapter 15
Section 1 Simple Invertebrates
Flatworms, continued
•Tapeworms Tapeworms are similar to flukes. Like
flukes, they have a small head with no eyespots or
sensory lobes.
• Tapeworms do not need a gut because they attach
directly to the host’s intestines and absorb nutrients.
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Chapter 15
Section 1 Simple Invertebrates
Roundworms
• Roundworms have bodies that are long, slim, and
round, like spaghetti. Like other worms, they have
bilateral symmetry.
• Roundworms have a simple nervous system. A ring of
ganglia forms a simple brain. Parallel nerve cords
connect the two ends of their body.
• Some round worms eat dead tissue. Many
roundworms are parasites.
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Chapter 15
Section 2 Mollusks and Annelid Worms
Objectives
• Explain how mollusks eat, control body functions, and
circulate blood.
• Describe the four body parts that most mollusks have
in common.
• Describe the three kinds of annelid worms.
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Chapter 15
Section 2 Mollusks and Annelid Worms
Mollusks
• Snails, slugs, clams oysters, squids, and octopuses
are all mollusks.
• Most mollusks fit into three classes:
• The gastropods include *.
• The bivalves include *
• The cephalopods include *.
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Chapter 15
Section 2 Mollusks and Annelid Worms
Mollusks, continued
• Each kind of mollusk has its own way of eating.
• Slugs and snails eat with a *
• Clams and oysters attach to one place and use
gills to filter tiny plants, bacteria, and other
particles from the water.
• Squids and octopuses grab food with tentacles
and place it in their powerful jaws.
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Chapter 15
Section 2 Mollusks and Annelid Worms
Mollusks, continued
• Ganglia and Brains All mollusks have complex
ganglia. They have ganglia to control breathing,
movement, and digestion.
• Cephalopods, such as octopuses, have large brains
that connect all of their ganglia. Cephalopods are
thought to be the smartest invertebrates.
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Chapter 15
Section 2 Mollusks and Annelid Worms
Mollusks, continued
• Pumping Blood Most mollusks have an open
circulatory system. In an open circulatory system, *
• Squids and octopuses have a closed circulatory
system. In a closed circulatory system, a *
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Section 2 Mollusks and Annelid Worms
Mollusks, continued
• Mollusk Bodies A snail, a clam, and a squid look
quite different from one another, yet they share similar
structures.
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Chapter 15
Section 2 Mollusks and Annelid Worms
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Chapter 15
Section 2 Mollusks and Annelid Worms
Annelid Worms
• Annelid worms are often called segmented worms
because their bodies have segments. A segment is*.
• Annelid worms have bilateral symmetry, a closed
circulatory system and a complex nervous system
with a brain.
• Annelid worms live in salt water, fresh water, or on
land. They eat plant material or animals.
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Section 2 Mollusks and Annelid Worms
Annelid Worms, continued
• Earthworms Earthworms are the most common
annelid worms.
• Each earthworm has 100 to 175 segments. Most
segments are identical, but some have special jobs,
such as eating or reproducing.
• Earthworms eat soil. Their castings, or waste,
improves soil quality.
• To move, earthworms use stiff hairs, or bristles, on
the sides of their bodies.
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Chapter 15
Section 2 Mollusks and Annelid Worms
Annelid Worms, continued
• Marine Worms Marine worms are covered in
bristles and come in many colors.
• Most marine worms live in the ocean. Marine worms
eat mollusks, other small animals, or filter food from
the water.
• Leeches Some leeches are parasites that suck
other animals’ blood. Other leeches eat dead animals
or hunt insects, slugs, and snails.
• Doctors use leeches to prevent swelling.
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Chapter 15
Section 3 Arthropods
Objectives
• List the four main characteristics of arthropods.
• Describe the different body parts of the four kinds of
arthropods.
• Describe the two types of metamorphosis in insects.
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Chapter 15
Section 3 Arthropods
Characteristics of Arthropods
• Arthropods share four characteristics: a segmented
body with specialized parts, jointed limbs, an
exoskeleton, and a well-developed nervous system.
• Segmented and Specialized Like annelid worms,
arthropods are segmented. Many also have
specialized parts such as *
• Jointed Limbs Jointed limbs are legs or other body
parts that bend at the joints and make moving easier.
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Section 3 Arthropods
Characteristics of Arthropods, continued
•An External Skeleton * is called an exoskeleton.
The exoskeleton supports the body, protects internal
organs, and prevents water loss.
• Sensing Surroundings Arthropods that have
compound eyes can see images. A compound eye *
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Section 3 Arthropods
Kinds of Arthropods
• Arthropods are classified by the kinds and numbers
of body parts they have.
• An antenna is a *
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Section 3 Arthropods
Kinds of Arthropods, continued
• Centipedes and Millipedes Centipedes and
millipedes have one pair of antennae, a hard head,
and one pair of mandibles. Mandibles *
• Centipedes have one pair of legs on each segment
and a total of 30 to 354 legs.
• Millipedes have two pairs of legs on each segment
and as many as 752 legs.
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Section 3 Arthropods
Kinds of Arthropods, continued
• Crustaceans Shrimps, barnacles, crabs, and
lobsters are crustaceans.
• Crustaceans have gills for breathing, mandibles for
eating, two compound eyes on eyestalks, and two
pairs of antennae.
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Section 3 Arthropods
Kinds of Arthropods, continued
• Arachnids Spiders, scorpions, mites, and ticks are
arachnids.
• Arachnids have two main body parts: a
cephalothorax and an abdomen.
• Most arachnids have four pairs of legs, no antenna,
simple eyes, and mouth parts called chelicerae.
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Chapter 15
Section 3 Arthropods
Body Parts of Arachnids
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Section 3 Arthropods
Kinds of Arthropods, continued
• Insects Insects make up the largest group of
arthropods. If you put all the insects in the world
together, they would weigh more than all the other
animals combined!
• Insects have three main body parts, six legs, and two
antennae.
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Chapter 15
Section 3 Arthropods
The World of Insects
• Insect Bodies An insect’s body has three parts: the
head, the thorax, and the abdomen.
• Metamorphosis is a phase in the life cycle of many
animals during which a *
• Complete Metamorphosis Most insects go through
a complete metamorphosis. Complete metamorphosis
has four parts: *
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Section 3 Arthropods
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Section 3 Arthropods
The World of Insects, continued
• Incomplete Metamorphosis Grasshoppers and
cockroaches are some of the insects that go through
incomplete metamorphosis.
• Incomplete metamorphosis has three main stages: *
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Chapter 15
Section 3 Arthropods
Incomplete Metamorphosis
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Chapter 15
Section 4 Echinoderms
Objectives
• Describe the endoskeleton, nervous system, and
water vascular system of echinoderms.
• Explain how an echinoderm’s body symmetry
changes with age.
• Describe five classes of echinoderms.
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Chapter 15
Section 4 Echinoderms
• Echinoderms are spiny invertebrates that live in the
ocean.
• Sea stars, sea urchins, and sand dollars are some
familiar members of this group.
• Echinoderms eat shellfish, dead plants or animals, or
algae that they scrape off rocks.
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Chapter 15
Section 4 Echinoderms
Spiny Skinned
• The name echinoderm means *
• The spines are actually on the animals endoskeleton.
An endoskeleton in an internal skeleton made of bone
or cartilage.
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Section 4 Echinoderms
Bilateral or Radial?
• Adult echinoderms have radial symmetry. Larvae
have bilateral symmetry.
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Section 4 Echinoderms
The Nervous System
• All echinoderms have a simple nervous system
similar to that of a jellyfish. Around the mouth is a circle
of nerve fibers called the nerve ring.
• Sea stars have a radial nerve that runs from the nerve
ring to the tip of each arm.
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Chapter 15
Section 4 Echinoderms
Sea Star Nervous System
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Section 4 Echinoderms
Water Vascular System
• The water vascular system is a *
• Echinoderms use their water vascular system to *
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Section 4 Echinoderms
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Section 4 Echinoderms
Kinds of Echinoderms
• There are five major classes of echinoderms. Sea
stars are the most familiar class.
• Brittle Stars and Basket Stars Brittle stars and
basket stars look like sea stars. But these echinoderms
have long, slim arms and are often smaller than sea
stars. They don’t have suckers on their tube feet.
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Section 4 Echinoderms
Kinds of Echinoderms, continued
• Sea Urchins and Sand Dollars Sea urchins and
sand dollars are round. Their endoskeletons form a
solid, shell-like structure.
• Sea Lilies and Feather Stars Sea lilies and feather
stars have 5 to 200 feathery arms.
• Sea Cucumbers Like sea urchins and sand dollars,
sea cucumbers have no arms. A sea cucumber has a
soft, leathery body.
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