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GUIDE FOR READING
29-1 Echinoderms
After you read the following
sections, you will be able to
CHAPTER
Guide For Reading
What are echinoderms?
29-1 Echinoderms
• Relate the structure of
echinoderms to essential life
How do echinoderms carry out essential functions?
¦ How are echinoderms classified?
¦ How do echinoderms affect other living things?
functions.
• Describe the characteristics of
Echinoderms
and
Invertebrate
Chordates
the classes of echinoderms.
• Explain how echinoderms fit into
the world.
29-2 Invertebrate Chordates
• Name and discuss the three
distinguishing characteristics of
chordates.
Nearly everyone who has visited the seashore has seen
starfish, sea urchins, sand dollars, or their remains washed up
on the beach. These animals are members of the phylum
Echinodermata (echino- means spiny; dermis means skin), a
phylum that has a long and fascinating history stretching back
to the beginning of the Cambrian Period, more than 580 million
years ago.
• Describe the two subphyla of
invertebrate chordates.
Journal Activity
YOU AND YOUR WORLD
The delicate symmetrical appearance of this starfish
obscures the fact that starfish are carnivores preying
on other forms of sea life. The small tunicate shown in
the inset is closely related to vertebrate animals, even
though its appearance more closely resembles other
simpler animals.
Perhaps you have combed a beach
for treasures of shells, starfish, or
sea-urchin spines, scrambled over
grassy dunes, swum in the ocean,
or imagined what the seashore is
like, In your journal, describe your
experiences, whether they are real
or imagined.
hen most people see a starfish, they immediately think of the
ocean—an appropriate reaction, considering that starfish and their
relatives live only in the sea. Surprisingly not all of the members of
this phylum resemble stars. Some look like graceful long-stemmed
flowers; others, like a peculiar cross between a polka-dotted pickle
and a stalk of cauliflower. Some are as round and prickly as a
pincushion. Others are flat bristly disks with holes and notches
around their edges. Still others resemble armored feather dusters,
closely related to the vertebrates? You will discover the answers to
Figure 29-1 Echinoderm means
spiny skin, which as you can see
from this sea urchin (bottom) is
an appropriate name. The sea
cucumber (top) is also an
echinoderm. Although its skin is
smooth, it shows another
characteristic of echinoderms—
these questions-'in the pages that follow.
five-part symmetry.
pentagon-shaped cookies, or the curlicues and flourishes beneath
ah old-fashioned signature.
What other animals belong to this phylum? How are they all
adapted to the ocean world? Why do scientists consider them to be
What Is an Echinoderm?
As their name indicates, echinoderms (ee-KlGH-nohdermz) are spiny-skinned animals. In addition to having a
spiny skin, echinoderms are characterized by five-part
radial symmetry, an internal skeleton, a water vascular
system, and suction-cuplike structures called tube feet. The
internal skeleton, or endoskeleton, is made up of hardened
plates of calcium carbonate, which are often bumpy or spiny.
Figure 29-2 Starfish, or sea star,
species vary greatly. This bat star
lives in the ocean off the coast of
southern California. Lacking the thin
arms of other starfish, this species
resembles a pentagon.
The water vascular system, which you will learn more about
shortly, consists of an internal network of fluid-filled canals
connected to external appendages called tube feet. The water
vascular system is involved with many essential life functions
in echinoderms, including feeding, respiration, internal trans¬
port, elimination of waste products, and movement.
Some echinoderms, such as starfish and sand dollars, live
in shallow water and are thus familiar to beach-goers. Other
echinoderms live only on coral reefs or on the floor of the deep
ocean. Although echinoderms possess certain characteristics
found in no other animals, living or extinct, they share several
important features with members of our own phylum (Chordata). For example, certain stages in the development of echinoderm larvae are remarkably similar to stages seen in some
members of the phylum Chordata. In addition, echinoderms
have an internal skeleton (as do vertebrates) rather than an ex¬
ternal skeleton (as do other invertebrates). For these reasons,
biologists believe that among common invertebrates, echino¬
derms are most closely related to humans.
Echinoderm species vary greatly in appearance. Starfish
exhibit a fragile beauty and perfection in shape that stirs
wonder in most observers. Some sea cucumber species fasci¬
nate because their ugliness has a certain repulsive appeal.
Regardless of appearance, however, echinoderms have adapta¬
tions that make them successful survivors in the world of the
sea. As you read this section, keep in mind that echinoderms
are survivors of history. Their success is confirmed by the fact
that some echinoderms alive today look much like their an¬
cient ancestors who lived in the seas millions and millions of
years ago.
Form and Function in Echinoderms
Adult echinoderms have a body plan with five parts organ¬
ized symmetrically around a center. As a result of this body
plan, adult echinoderms typically have neither an anterior nor
a posterior end and no brain. However, most echinoderms are
two-sided. The side where the mouth is located is called the
oral surface, and the opposite side is called the aboral surface.
All echinoderms have a unique system of internal tubes
called a water vascular system. The water vascular system
opens to the outside through a sievelike structure called the
madreporite (ma-druh-POR-ight). In starfish, the madreporite
connects to a tube called the ring canal that forms a circle
around the animal's digestive system. From the ring canal, five
radial canals extend into each body segment. Attached to each
radial canal are hundreds of movable tube feet. The entire
water vascular system operates like a series of living hydraulic
pumps that can propel water in or out of the tube feet. When
water is pushed into a tube foot, the tube foot expands. When
water is pulled out, the cup on the end of the tube foot shrinks,
Upper
part of
stomach
creating a partial vacuum that holds onto whatever the foot is
touching. In this way, the tube feet act like living suction cups.
A single tube foot alone cannot accomplish much, but
hundreds acting together create enormous force. All echino¬
derms "walk" with their tube feet, and some use their tube feet
for feeding.
FEEDING Echinoderms have several methods of feeding.
Carnivores, such as many species of starfish, use their tube feet
to pry open the shells of bivalve mollusks such as clams and
scallops. Once the bivalve's shell is opened, the starfish flips
its stomach out of its mouth, pours out enzymes, and digests its
prey in the prey's own shell. When the starfish has finished
dining, it moves its stomach back into its mouth, leaving be¬
hind an empty shell as the only evidence of its deed. Starfish
also eat snails, corals, and even other echinoderms. Herbi¬
vores, such as sea urchins, scrape algae from rocks by using
their five-part jaw. Filter feeders, such as sea lilies, basket
stars, and some brittle stars, use tube feet on flexible arms to
capture plankton that float by on ocean currents. Detritus
feeders, such as sea cucumbers, move much like a bulldozer
across the ocean floor, taking in a mixture of sand and detritus.
Then, like an earthworm, they digest the organic material and
pass the sand grains out in their feces.
Lower
part of
stomach
Figure 29-3 The pressure exerted
by the water vascular system of the
starfish (left) moves the animal
along the ocean bottom. The
digestive system of a starfish (right)
breaks down food, which is then
transported throughout the animal's
body in the digestive glands and in
the fluid within the body cavity.
RESPIRATION Echinoderms, like other animals, need to
exchange carbon dioxide for oxygen. In most species the thinwalled tissue of the tube feet forms the main respiratory sur¬
face. In some species small outgrowths called skin gills also
function in gas exchange.
INTERNAL TRANSPORT The functions of transporting
oxygen, food, and wastes—which are performed by the circula¬
tory system in many animals—are shared by different systems
639
spiny defenses of echinoderms. For example, basket stars,
feather stars, and spiny sea urchins are very slow moving.
Clever fishes (and you will meet some clever fishes in Chapter
31) have learned to turn these animals over and attack them
through their unprotected underside. For this reason, many
echinoderms hide under rocks and in crevices by day, coming
out to feed at night, when most predators are asleep.
Figure 29-4 Tube feel, located on
the underside of a starfish's arms,
are used to perform many life
functions (left). Starfish use their
tube feet to open clams (right). Once
the starfish has opened the clam
shell, it flips its stomach out of its
mouth and begins to digest the clam
right in the shell. No wonder starfish
are not welcome in clam beds!
in echinoderms. Because respiration (gas exchange) and the
removal of metabolic wastes occur through skin gills and tube
feet located all over the body, a system to deliver oxygen and
carry away carbon dioxide and other wastes is not essential.
The distribution of nutrients is performed primarily by the di¬
gestive glands and the fluid within the body cavity.
EXCRETION In almost all echinoderms, solid wastes are
released through the anus in the form of feces. (The exceptions
are brittle stars, which lack an anus and thus release undi¬
gested materials through the mouth.) Echinoderms, like many
other marine invertebrates, excrete nitrogen-containing cellu¬
lar wastes primarily in the form of ammonia. Wastes seem to be
excreted in many of the same places around the body in which
gas exchange takes place—the tube feet and the skin gills.
RESPONSE As you might expect in animals that have no
head, echinoderms have primitive nervous systems. Most
echinoderms have a nerve ring that surrounds the mouth and
radial nerves that connect the ring with the body sections.
Scattered sensory cells that are sensitive to chemicals released
by potential food are also characteristic of most species. Star¬
fish additionally have up to 200 light-sensitive cells clustered
in eyespots at the tip of each arm. Although these structures
have lenses, they do little more than tell the animal whether it
is light or dark. Some echinoderms also possess statocysts
(simple organs for balance that tell an organism whether it is
right side up).
Although you might think that the tough, spiny skins of
echinoderms protect them from predators, spines actually offer
protection for only a few species—the crown-of-thorns starfish,
for example." Many predators have learned ways around the
MOVEMENT Most echinoderms use tube feet and thin
layers of muscle fibers attached to the plates of the endoskeleton to move. An echinoderm's mobility is determined in part
by the structure of its endoskeleton, In sand dollars and sea ur¬
chins, the plates are fused together to form a rigid box that en¬
closes the animal's internal organs. These animals usually have
movable spines attached to their endoskeleton, which they use
along with their tube feet to creep from one place to another or
to burrow in the sand. In starfish, brittle stars, and feather
stars, the skeletal plates move around a series of flexible joints,
enabling these echinoderms to use their arms for locomotion.
Feather stars can swim for short distances by flapping their
arms like wings, but starfish and brittle stars are only able to
crawl. In sea cucumbers, the plates are reduced to tiny vestiges
inside a soft, muscular body wall. The loss of the plates makes
the body of sea cucumbers very flexible. Some species are able
to crawl along the ocean floor like large, fat worms by contract¬
ing the muscles of the body wall.
Figure 29-5 The basket star
spreads its branching arms to filter
particles of food from the water.
When disturbed, the basket star curls
up these arms and exposes the
armored surface for protection.
REPRODUCTION Most echinoderms are either male or
female, although some are hermaphrodites. In starfish, the
sperm or eggs are produced in testes or ovaries, respectively,
which fill the arms during the reproductive season. The ani¬
mals shed their sperm and eggs into the water. Individual star¬
fish detect gametes of their own species in the water, and they
respond to that stimulus by releasing their own gametes. Fertil¬
ization takes place in open water, and larvae swim around for
some time as members of the huge community of plankton that
swarm in the ocean. Eventually the larvae, which have bilateral
symmetry, swim to the ocean bottom, where they mature and
metamorphose into adults that have radial symmetry.
Many starfish have incredible abilities to repair themselves
when damaged. In fact, if a starfish is pulled into pieces, each
piece can grow into a new animal as long as it contains a por¬
tion of the central part of the body. This ability of a starfish to
regenerate itself has caused a great deal of trouble to people
who earn their living fishing for bivalves (two-shelled mollusks). In the past, angry shellfishermen who were aware that
starfish ate bivalves would tear the animals into two or three
pieces and toss them overboard. Imagine their surprise when
they noticed even more starfish in their bivalve beds. Today,
shellfishermen know that starfish have the ability to regenerate
and that every piece of torn starfish they throw back could de-
Figure 29-6 Unlike adults, which
mostly crawl along the ocean
bottom, echinoderm larvae are free-
swimming. These larvae resemble
closely the free-swimming larvae of
invertebrate chordates.
641
The Echinoderm Classes
The almost 6000 species of living echinoderms are found in
almost every ocean in the world. However, no echinoderms
have ever entered fresh water, and they cannot survive for long
on land. Although they share certain characteristics, echinoderm species are remarkably diverse in appearance. The fol¬
lowing descriptions of echinoderm classes will provide a brief
introduction to these animals.
STARFISH This class contains the common starfish,
which are also known as sea stars. Starfish occur in many
colors, and you may be surprised to learn that many species
have more than five arms. Starfish creep slowly along the
ocean bottom. Most are carnivorous, preying upon the bivalves
they encounter as they move. Some species of starfish are im¬
portant predators in rocky areas along the coast.
BRITTLE STARS These animals live in tropical seas,
Figure 29-7 The brittle star gets its
name from the fact that it can shed
its arms when it is threatened (left).
This distracts predators so that the
brittle star can escape. In time, it
wdl re grow the missing arm. Some
starfish, such as the sun star, have
more than hue arms (right).
especially on coral reefs. They look much like a common star¬
fish, but they have longer, more flexible arms and are thus able
to move much more rapidly. In addition to using speed for pro¬
tection, brittle stars protect themselves by shedding one or
more of their arms when attacked. The detached parts keep
wriggling violently, distracting predators, while the rest of the
animal escapes. Brittle stars are filter and detritus feeders that
hide by day and wander around in search of food only under
the cover of night.
SEA URCHINS AND SAND DOLLARS This class includes
disk-shaped sand dollars, oval heart urchins, and round sea ur¬
chins. Many of these animals, which are found in marine envi¬
ronments all over the world, are grazers that eat large
quantities of algae. Others are detritus feeders. Heart urchins
and sand dollars live hidden in burrows that they dig in sand
or mud. Most sea urchins wedge themselves in crevices in rock
during the day and come out only at night. However, many sea
urchins have formidable defenses in the form of long, sharp
spines. One type of sea urchin even has small blue poison sacs
covering the tips of each spine, ensuring that wounds it inflicts
will be painful!
SEA CUCUMBERS As their name implies, these echino¬
derms look like warty moving pickles with a mouth at one end
and an anus at the other. Most sea cucumbers are detritus
feeders. Although these animals are not numerous in shallow
water, herds containing hundreds of thousands of them often
cover areas of the sea floor at great depths. A few species of sea
cucumbers expel sticky substances that attach to a predator.
The predator, in all probability an attacking crustacean, is im¬
mobilized as it is glued into a helpless ball.
Figure 29-8 The slate urchin
(top, right) has thick, strong spines
that were once harvested for use
as implements for writing on
slateboards—thus, its name. Sea
urchins have a lanternlike set of
bony plates inside their body that
power their jaws (inset). The sand
dollar (top, left) gets its name
from its flattened, coin-shaped
appearance.
SEA LILIES AND FEATHER STARS These filter feeders,
which have 50 or more long, feathery arms, comprise the most
ancient class of echinoderms. Although sea lilies and feather
stars are not common today, a rich fossil record indicates that
643
they were once widely distributed. Sea lilies are sessile animals
that are attached to the ocean bottom by a long, stemlike stalk.
Modern sea lilies live at depths of 100 meters or more. Many
feather stars live on coral reefs, where they perch on top of
rocks at night and use their tube feet to catch floating plankton.
How Echinoderms Fit into the World
Echinoderms are numerous in most marine habitats. In
many areas, starfish are important carnivores that control the
populations of other animals. Sometimes their numbers rise or
fall suddenly, causing major changes in the numbers of other
forms of marine life. For example, several years ago the coraleating crown-of-thorns starfish suddenly appeared in great
numbers over wide areas of the Pacific Ocean. Within a short
span of time, these starfish caused extensive damage to many
coral reefs. The extent of their damage surprised and alarmed
marine biologists, many of whom took drastic action to kill the
starfish by injecting them with poisonous chemicals. We still do
not know what caused this population explosion in the crownof-thorns starfish or what will be its long-term effects on coral
reefs.
Figure 29-9 Acting much like a
living vacuum cleaner, this sea
cucumber (top) moves along the
ocean bottom swallowing organic
material along with sand. Sea lilies
(center) and feather stars (bottom)
feed by filtering floating organic
material from the water. The names
reflect the delicate beauty of these
animals.
In many coastal areas, sea urchins are important because
they control the distribution of algae. However, if present in
large numbers, they can threaten to literally "eat out of house
and home" the other dwellers that share this habitat.
In various parts of the world, some echinoderms—for ex¬
ample, sea urchin eggs and sea cucumbers—are considered
delicacies by some people. Many more echinoderms, however,
are useful as research subjects and as possible sources of medi¬
cine. Several chemicals extracted from starfish and sea cucum¬
bers are currently being studied as potential anti-cancer and
anti-viral drugs. Sea urchins have been the subject of pioneer¬
ing studies in embryology. These animals are easy to study be¬
cause they produce large eggs that are fertilized externally and
develop in plain sea water. Sea urchin embryos also make ex¬
cellent subjects for testing the effects of drugs on cell division
and development.
SECTION
REVIEW
1. What is an echinoderm? Name five kinds of
echinoderms.
2. How do tube feet help echinoderms to carry out their
essential life functions?
3. How do starfish move? How do starfish open bivalves?
4. Connection—Ecology Why is tearing a starfish apart
and throwing it back into the water not a good way to
limit a starjish population?
644
29-2 Invertebrate Chordates
Guide For Reading
The phylum Chordata. to which fishes, frogs, birds, snakes
dogs cows and humans belong, will be the subject of many of
the chapters to come. Most of the chordates
vertebrates, which means that they have backbones, so they
are placed in the subphylum Vertebrata. But there are also
some invertebrate chortates. The ¦"-rtebrate chordates are
divided into two subphyla-tumcates and lanceleta Because
thev show possible links between vertebrates and the rest o
the animal kingdom, the invertebrate chordates are of great
What are chordates? What are
invertebrate chordates?
What are the distinguishing
characteristics of chordates?
Why are invertebrate chordates
important to evolutionary
biologists?
evolutionary interest.
What Is a Chordate?
Members of the phylum Chordata are chorda^'
Chordates are animals that are characterized by a notochord a hollow dorsal nerve cord, and pharyngeal (thro )
slits Some chordates possess these distinguishing characteris¬
es as adults; Others, only as embryos. However, all chorda es
display these three characteristics at some stage of their lite.
The first chordate characteristic, the notochord, m a lonsh
flexible supporting rod that runs through at least part of the
body usually along the dorsal surface just beneath the nerve
cord' Most chordates have a notochord only during the early
part of embryonic life. In most vertebrates, the notochord is
-^VtSrirracteristic, the hollow do.al
nerve cord runs along the dorsal surface just above the noto¬
chord. Remember that in most invertebrates, nerve cords run
along ventral surfaces. In most chordates, the front end of this
nerve cord develops into a large brain. Nerves 'his cord
at regular intervals along the length of the animal and connect
to internal organs, muscles, and sense organs.
The third chordate characteristic, pharyngeal slits are
paired structures in the pharyngeal (fuh-RmH-jee-uhO o
throat, region of the body, (Remember that pharynx anothe
word for throat.) In aquatic chordates such as lancelets and
fishes the pharyngeal slits are gill slits that connect the pharvngeal cavUy ^th the outside. The location of gills is very im¬
portant Many invertebrates have gills of some sort in variou
places but only chordates have pharyngeal gills. In terrestna
chordates that use lungs for respiration, pharyngeal slits are
present for only a brief lime during the development of he embrvo These slits soon close up as the embryo develops In
chordates such as humans, pouches form in the pharyngeal reion but never open up to form slits, ^r this reason some sci¬
entists regard pharyngeal pouches, not slits, as the
chordate characteristic.
TUNICATES Tunicates are small marine chordates that
eat plankton they filter from the water. They get their name
Figure 29-10 Although it seems
like a simple animal, the tunicate is
a chordate. It is, therefore, a relatwe
of ours—although a very distant
one.
from a special body covering called the tunic. Only the tad¬
pole-shaped larvae of tunicates have a notochord and a dorsal
nerve chord. When most tunicate larvae mature, they undergo
metamorphosis and become sessile adults that grow into colo-
aTltsirf h0 3 ^ SUrfaCe- B0th 'arval tunicates and
adults filter feed and breathe at the same time through a pha¬
ryngeal basket pierced by gill slits.
LANCELETS The small fishlike creatures called lancelets
ive in the sandy bottom of shallow tropical oceans. Unlike tun¬
icates, adult lancelets have a definite head. They have a mouth
nair.Tf^n1".-? a, g Pharyn§eaI region with up to a hundred
pairs of gill slits. Lancelets feed by passing water through their
pharynx, where food particles are caught in a sticky mucus.
is mucus is swallowed into a digestive tract that starts at one
nd of the pharynx and continues straight through the animal
to the anus, near the tail.
^aVe 3 simP,e' P"mitive heart that pumps blood
Figure 29-11 Sea squirts are
tunicates. /Ls' adults, these organisms
are sessile, living firmly attached to
one place. However, the larvae of
these animals, like the larvae of
echinoderms, are free-swimming.
The Secret Life of Salps
once mysterious open-water tunicates known
Once scuba-diving scientists became suffi¬
ciently experienced (and sufficiently brave) to
hop off their boats in the middle of the ocean,
however, our knowledge of salps increased
dramatically. It became clear that salps are
everywhere. Giant herds of salps drift just be¬
neath the surface. Certain species form huge
snakelike colonies that stretch for many
Sometimes a remarkably simple change in
the techniques biologists use to study the
world causes us to alter our ideas about the
way the living world works. For example, the
invention of the microscope opened up the
world of "unseen life." Recently, new methods
have contributed to our understanding of the
as salps.
meters.
lanrf»i t Ve*seis In a closed circulatory system. Additionally,
ancelets show evidence of segmentation in the arrangement of
n nerves and muscles. A lancelet's muscles are organized
to V-shaped units that are paired on either side of the body
Each muscle unit receives a branch from the main nerve cord
A similar segmented nerve and muscle organization is found in
all living vertebrates. Unlike most vertebrates, lancelets have
no jaw. Their mouth is composed entirely of soft tissues. LanceJets also lack appendages and can move only by bending
their bodies back and forth. 8
Salps are free-swimming animals that live
in the open sea. Biologists have known about
their existence for many years, but they knew
little about their importance. This was due to
the fact that research vessels had no way of
collecting and identifying salps. These beauti¬
ful animals are so fragile that they literally fall
to pieces if they are handled roughly. And that
was exactly what happened in the collecting
nets marine biologists used to gather plankton.
Any salps that entered the net were squeezed
How Invertebrate Chordates Fit
into a clear, featureless mush.
By collecting salps carefully, researchers
have learned how they live. In many places,
salps form important links in the ecology of
the open sea. Salps eat certain plankton and
are themselves food for other plankton, sea
turtles, and certain fishes. This new knowledge
has come to light because of a simple change
in research techniques. Although these vital
creatures have been nearly ignored for dec¬
ades, marine biologists can now study them
closely and discover how they fit into the web
of life.
into the World
Figure 29-12 Lancelets are small
fish/ike creatures that often live with
their body half buried in sand. They
filter food particles from the water.
In some ways, studying invertebrate chordates is like using
a time machine to study the ancestors of our own subphylum. It
is important to remember that living vertebrates did not evolve
from hying lancelets or tunicates. Both these subphyla have
evolved oyer time. However, similarities in structure and embryolog'cal development indicate that vertebrates and inverteb ate chordates evolved from common ancestors many
millions of years ago.
1. What characteristics are found in a chordate?
2. What characteristics of tunicates and lancelets make
them seem like close relatives of vertebrates?
3. Critical Thinking—Making Comparisons Which
characteristics of tunicates and lancelets are unlike
vertebrate cbaracteristics?
Salps are free-swimming invertebrate chordates found in the open ocean.
647
r u d E imj
S 1r ii ii ¥
6 I %&
•v 1
G ECHINODERMS
PROBLEM
SUMMARIZING THE CONCEPTS
How can echinoderms be identified?
Specimen
Identity of Specimen
Identification (from Identification Key)
MATERIALS (per group)
Number
1
assorted echinoderms
(pictures or preserved specimens)
29-1 Echinoderms
2
• Echinoderms are spiny-skinned animals with
five-part radial symmetry, an internal skele¬
3
4
PROCEDURE
L^-
1. On a separate piece of paper, draw a data table
similar to the one shown here.
2. Your teacher will provide either pictures or
preserved echinoderm specimens. Each speci¬
men will be numbered.
3. Use the key to identify each numbered speci¬
men. Start at step 1 and read descriptions A
and B. Only one of the descriptions correctly
applies to the specimen you are examining. At
the end of a description is the identity of the
specimen or directions to proceed to another
step. Continue to follow the directions step by
step until you identify the specimen.
4. After you identify the specimen, write its name
next to its identification number in the data
table. Then proceed to the next numbered
derms are important predators in many
environments.
ton, a water vascular system, and suction-
—-
OBSERVATIONS
1. What feature did all of the echinoderms you
examined have in common?
2. How did the echinoderms you examined
differ?
3. Did any echinoderms with visible differences
have the same identity?
ANALYSIS AND CONCLUSIONS
1. How is the use of an identification key similar
to the process of classification?
2. Why is it possible for two organisms that look
different to have the same identity based on
specimen.
The key concepts in each section of this chapter are listed below to help you
review the chapter content. Make sure you understand each concept and its
relationship to other concepts and to the theme of this chapter.
the key used in this investigation?
29-2 Invertebrate Chordates
cuplike structures called tube feet.
• Echinoderms are marine animals; no echino¬
derms live in fresh water or on land. Certain
stages in the development of echinoderm
larvae are similar to stages seen in members
of the phylum Chordata.
• All echinoderms have a water vascular sys¬
tem that opens to the outside through a
sievelike structure called the madreporite.
• In a starfish, the madreporite connects to a
tube that leads to the ring canal, a part of the
water vascular system, which forms a circle
around the starfish's digestive system. Nu¬
trients are moved around the animal in the
digestive glands and the body cavity.
• Starfish reproduce externally by pouring
eggs and sperm into the ocean water. The
larvae that result from a fertilized egg float as
part of the plankton.
• In spite of their fragile appearance, echino¬
• Most chordates are vertebrates, which
means they have backbones. However, a few
chordate species are invertebrates. There
are two subphyla of invertebrate, chordates
—tunicates and lancelets.
• At some stage of their life, all chordates pos¬
sess these distinguishing characteristics: a
notochord, a hollow dorsal nerve cord, and
pharyngeal (throat) slits.
• Tunicates are small chordates that live in the
ocean. Tunicate larvae resemble tadpoles
and can move around in the water.
• Lancelets are small fishlike creatures that
live in sandy ocean bottoms. Adult lancelets
have a definite head.
9 Invertebrate chordates are important be¬
cause they indicate that vertebrate and in¬
vertebrate chordates evolved from common
ancestors many millions of years ago.
Identification Key
1 A. Has obvious radial symmetry
B. Appears to have bilateral symmetry
Go to 2
A. Has arms or branches
Cucumber
B. Spherical, oval, or disk shaped
Co to 3
3 A. Arms in multiples of five
Go to 5
B. Arms are branched and feathery Go to 4
4 A. Arms are long, slender, and flexible Go to 7
B, Arms are thick and less flexible
Star
o A. Spherical; covered with spines Starfish
B. Not spherical
Sea Urchin
6
AOval
Go
to
6
B. Flattened disk
Urchin
7 A. Has a long stalk
!.
Sand Dollar
B. Stalk short or absent
Sea Lily
'
648
'
""'
Feather
Star
REVIEWING KEY TERMS
Vocabulary terms are important to your understanding of biology. The key terms
listed below are those you should be especially familiar with. Review these terms
and their meanings. Then use each term in a complete sentence. If you are not
sure of a term's meaning, return to the appropriate section and review its definition.
29-1 Echinoderms
echinoderm
water vascular system
tube feet
29-2 Invertebrate
hollow dorsal
Chordates
nerve cord
chordate
notochord
pharyngeal slit
649
CONTENT REVIEW
B. In each of the following sets of terms, three of the terms are related. One term
does not belong. Determine the characteristic common to three of the terms and
then identify the term that does not belong.
Multiple Choice
Choose the letter of the answer that best completes each statement.
1. A kind of echinoderm that is eaten by some
5. Digested nutrients are moved around the
people is a
body of a starfish in its
a. sea urchin. c. starfish.
a. skin gills. c. bony plates.
b. digestive glands, d. water vascular
b. sea lily. (j lancelet.
2. To open a clam, a starfish uses its
system.
a. tube feet. c. madreporite.
b. brain. d stomach.
6. Tunicates and lancelets are examples of
a. vertebrates. c. echinoderms.
3. Echinoderms have
^ ^sh- d. chordates.
a. a backbone.
b. a long history on Earth.
c. lungs.
7. The side of an echinoderm where the
mouth is located is called the
a. aboral surface. c. oral surface.
d. smooth skin.
4. Echinoderms show
a. bilateral symmetry.
b. top and bottom symmetry.
b. tunicate. d. vascular surface.
8. Invertebrate chordates lack a
c. radial symmetry.
d. no symmetry.
a. larva. c. nerve cord.
b. notochord. d. backbone.
True or False
5.
6.
7.
8.
starfish, sea lily, lancelet, sea urchin
ring canal, radial canal, tube feet, skin
notochord, hollow dorsal nerve cord, pharyngeal slits, vertebrae
tube feet, brain, water vascular system, madreporite
CONCEPT MASTERY
Use your understanding of the concepts developed in the chapter to answer each
of the following in a brief paragraph.
5. How do starfish reproduce?
1. What is radial symmetry? Name an animal
6. How does a sea cucumber feed?
that shows this kind of symmetry.
7. What characteristics does a lancelet share
2. Briefly explain how a starfish eats a clam.
with vertebrate chordates?
3. How does the water vascular system of a
8. Why is it not a good idea to break up a
starfish help this animal to move?
starfish and throw the pieces back into the
4. What structures on a starfish tell this
water, especially if you fish for oysters?
animal about its environment?
CRITICAL AND CREATIVE THINKING
Determine whether each statement is true or false If it
is true, write "true." If it
is false, change the underlined word or words to make
Discuss each of the following in a brief paragraph.
1. All echinoderms have bilateral symmetrv. fi
2. In echinoderms. tube feet and skin gills
used in respiration and excretion. 7
3. Lancelets have a primitive heart.
4. Echinoderms have nerves attached to 8
plates in their endoskeleton.
1. Making predictions Suppose that you are
living alone on a small tropical island in
the Pacific Ocean. This island is protected
by a coral reef that surrounds it. One day
while you are skin diving, you notice
several crown-of-thorns starfish eating some
of the coral animals that are part of your
the statement true.
5. A sea cucumber is a herbivore.
Tube feet are able to create suction when
air is pumped out of them.
Some echinoderms have madreporites that
tell them whether they are right side up.
If a piece of a starfish contains a portion of
the central part of the body, the piece is
able to regenerate.
Word Relationships
A. An analogy is a relationship between two pairs of words or phrases senera/lv
wrmen ,n the fo lowing manner: abed. The symbol: is read Cto'andthe
anTa'l aj^ls toplan,^^ ^ * -
reef. Predict what might happen if the
crown-of-thorns starfish increase in number.
2. Making comparisons Compare the form
and function of a starfish and a sea
cucumber. Describe the animals'
adaptations for movement and feeding.
3. Applying concepts Explain why many
1. starfish:echinoderm::tunicate:
2. sea cucumberrdetritus feeder::feather smr ~
3. eyespots:light::statocysts:
4. madreporite.aboral surface::mouth:__
fertilized starfish eggs never develop into
adult starfish.
4. Designing an experiment Your friend tells
you that starfish can regenerate themselves
from even a small portion of an arm. You
challenge this assumption. Design an
experiment to prove who is correct.
5. Using the writing process Suppose that
humans had the ability to regenerate
themselves. For example, an arm might be
able to grow a whole new body. Write a
science fiction story that describes how this
process might work for a person who was
severely injured in an automobile accident.