Download Most animals are invertebrates.

KEY CONCEPT
Most animals are
invertebrates.
Sunshine State
STANDARDS
SC.F.2.3.3: The student
knows that generally
organisms in a population live long enough
to reproduce because
they have survival
characteristics.
SC.G.1.3.3: The student
understands that the
classification of living
things is based on a
given set of criteria
and is a tool for understanding biodiversity
and interrelationships.
SC.H.2.3.1: The student
recognizes that patterns exist within and
across systems.
VOCABULARY
invertebrate p. 413
sponge p. 415
sessile p. 415
larva p. 416
BEFORE, you learned
NOW, you will learn
• Animals are consumers; they
get food from the environment
• Most animals have body systems,
including tissues and organs
• Animals interact with the environment and other animals
• About the diversity of
invertebrates
• About six groups of
invertebrates
• How sponges get energy
THINK ABOUT
What makes an
animal an animal?
A sponge is an animal.
It has no head, eyes, ears, arms,
or legs. A sponge doesn’t have a
heart or a brain or a mouth. It
doesn’t move. Typically, it spends its life
attached to the ocean floor. Many people used to think that
sponges were plants that had adapted to life in the water. Scientists,
however, classify them as animals. How might you decide if the organism in the photograph is an animal?
Invertebrates are a diverse group
of organisms.
COMBINATION NOTES
Make notes and diagrams for the first main
idea: Invertebrates are a
diverse group of organisms. Include a sketch of
a member of each group.
About one million invertebrate species live on Earth. Invertebrates
are animals that do not have backbones. In fact, invertebrates do not
have any bone tissue at all. Invertebrates can be found just about
everywhere, from frozen tundra to tropical forests. Some invertebrates
live in water, while others survive in deserts where there is almost no
water. Many invertebrates live inside other organisms.
Most invertebrate animals are small. Crickets, oysters, sea stars,
earthworms, ants, and spiders are some examples of invertebrates.
The fact that invertebrates do not have backbones for support tends to
limit their size. However, some ocean-dwelling invertebrates can be
quite large. For example, the giant squid can grow to 18 meters (59 ft)
in length and can weigh over 450 kilograms (992 lb).
Chapter 12: Invertebrate Animals 413
Invertebrates
Which types of invertebrates live near you?
SKILL FOCUS
Observing
PROCEDURE
1
Cut the potato in half lengthwise. Scoop out a hole and carve a channel so it
looks like the photograph below.
2 Put the two halves back together and wrap them with masking tape. Leave
the channel uncovered. It is the entrance hole.
3 Take the potato trap outside and bury it upright in soil, with the entrance
hole sticking out of the ground. Wash your hands.
4 Collect the potato the next day. Remove the masking tape and look inside.
MATERIALS
•
•
•
•
potato
knife
spoon
masking tape
TIME
20 minutes
WHAT DO YOU THINK?
• Observe the contents of the potato. Record your observations.
• Would you classify the contents of the potato as living or nonliving?
Do you think they are animals or plants?
CHALLENGE Predict how your observations would be
different if you buried the potato in a different place.
In this chapter, you will learn about six groups of invertebrates:
are the simplest invertebrates. They live in water. They
filter food from the water that surrounds them.
Cnidarians also live in water. Animals in this group have a central opening surrounded by tentacles. They take in food and
eliminate waste through this opening. Jellyfish, sea anemones,
hydras, and corals are cnidarians.
Worms are animals with soft, tube-shaped bodies and a distinct
head. Some worms live inside other animals. Others live in the
water or on land.
Mollusks have a muscular foot that allows them to move and
hunt for food. Some mollusks live on land. Others live in water.
Clams, snails, and octopuses are mollusks.
Echinoderms are water animals that have a central opening for
taking in food. Sea stars and sand dollars are echinoderms.
Arthropods are invertebrates that are found on land, in the
water, and in the air. They have legs. Some have wings. Insects,
spiders, crabs, and millipedes are arthropods.
• Sponges
•
•
•
•
•
414 Unit 3: Diversity of Living Things
Sponges are simple animals.
Sponges are
the simplest multicellular animals on Earth. These invertebrates are sessile (SEHS-EEL) organisms, which means they live
attached to one spot and do not move from place to place. Most live in
the ocean, although some live in fresh water. Sponges have no tissues
or organs. The body of a sponge is made up of a collection of cells.
The cells are organized into a body wall, with an outside and an
inside. Sponges are adapted to feed continuously. They feed on plankton and other tiny organisms that live in the water.
VOCABULARY
Make a description wheel
for sponge. Include information on its specialized
cells.
Specialized Cells
A sponge meets its needs with cells specialized for different functions.
Pore cells along the body wall create tiny openings throughout the
body. The pores lead into larger canals and sometimes a central opening, where cells with tiny hairs, or flagella, move water through the
sponge. As water moves out, more water enters, as shown in the diagram below. Specialized cells filter out food particles and oxygen.
Other specialized cells digest the food.
Check Your Reading
What adaptations does a sponge have for obtaining food?
Feeding in Sponges
Structures in a sponge’s body function
to remove food from water.
2
Flagella along the inside
of the sponge move water
through the sponge.
1
Water flows into
the sponge
through pores in
the body wall.
flow of
water
3
4
Specialized cells digest
the food particles.
inside of
sponge
Specialized cells
pick up food
particles as the
water moves by.
pores
Chapter 12: Invertebrate Animals 415
Another adaptation sponges have are structures that make the
body stiff. Most sponges have spicules (SPIHK-yoolz), which are
needlelike spines made of hard minerals such as calcium or silicon.
Spicules help give the sponge its shape and provide support. In some
sponges, spicules stick out from the body. This may make the sponge
less likely to become a source of food for other animals.
Reproduction
Sponges can reproduce asexually. Buds form alongside the parent
sponge or the buds break off and float away. Tiny sponges can float
quite a distance before they attach to the ocean floor or some underwater object and start to grow.
Sponges also reproduce sexually, as most multicellular organisms
do. In sponges, sperm are released into the water. In some sponges, the
eggs are released too. In this case, fertilization occurs in the water. In
other sponges, the eggs are contained in specialized cells in the body
wall. Sperm enter the sponge to fertilize the eggs.
A fertilized egg becomes a larva. A larva is an immature form—an
early stage—of an organism that is different from the parent. Sponge
larvae are able to swim. They move away from the parent and will
grow into a sponge once they attach to some underwater surface.
Then they become sessile, like their parents.
This basket sponge is
releasing microscopic
larvae into the water.
Sponges provide a good starting point for studying other invertebrates. There are many different types of invertebrates, with a wide
range of body structures and behaviors. Invertebrates have adapted to
many different environments. But the sponge is a simple organism
that has changed very little over time. Sponges today look very similar
to fossil sponges that are millions of years old.
KEY CONCEPTS
CRITICAL THINKING
1. Make a table with six columns.
Write the name of an invertebrate group above each
column. Fill in the table with a
characteristic and an example
for each group.
4. Apply Give two examples of
how structure in a sponge
relates to function. You should
use the words flagella and
spicule in your answer.
2. What does it mean that
sponges are sessile?
3. How do sponges meet their
need for energy?
416 Unit 3: Diversity of Living Things
5. Infer How is water involved
in the reproductive cycle of
a sponge?
CHALLENGE
6. Analyze Sponges have lived
on Earth for hundreds of millions of years. Sponges today
look very similar to fossil
sponges. What does this suggest about how well the
simple structure of a sponge
meets its needs? Do species
always change over time?