Chapter 38
Echinoderms and Invertebrate
Chordates
Table of Contents
Section 1 Echinoderms
Section 2 Invertebrate Chordates
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Chapter 38
Section 1 Echinoderms
Objectives
• Discuss four distinguishing characteristics of
echinoderms.
• Describe representative species from each of the
five classes of echinoderms.
• Describe the water-vascular system and other major
body systems of echinoderms.
• Compare sexual and asexual reproduction in sea
stars.
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Chapter 38
Section 1 Echinoderms
Characteristics
• Echinoderms are radially symmetrical
deuterostomes.
• Most living species of echinoderms are motile, but
some are sessile.
• Most echinoderms have:
– pentaradial symmetry
– an endoskeleton made up of ossicles
– a water-vascular system
– tube feet
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Chapter 38
Section 1 Echinoderms
Classification
• There are about 7,000 species of echinoderms.
• There are five major classes of echinoderms:
– Crinoidea
– Ophiuroidea
– Echinoidea
– Holothuroidea
– Asteroidea
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Chapter 38
Section 1 Echinoderms
Classification, continued
Class Crinoidea
• Members of the class Crinoidea, called crinoids,
include the sea lilies and feather stars.
• In both types of crinoids, five arms extend from the
body and branch to form many more arms—up to
200 in some feather star species.
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Chapter 38
Section 1 Echinoderms
Classification, continued
Class Ophiuroidea
• The 2,000 species of basket stars and brittle stars
make up the largest echinoderm class, Ophiuroidea,
which means “snake-tail.”
• Members of this class are distinguished by their long,
narrow arms, which allow them to move more quickly
than other echinoderms.
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Chapter 38
Section 1 Echinoderms
Classification, continued
Class Echinoidea
• The class Echinoidea consists of about 900 species
of sea urchins and sand dollars.
• Echinoidea means “spinelike.”
• The internal organs are enclosed within a fused, rigid
endoskeleton called a test.
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Chapter 38
Section 1 Echinoderms
Classification, continued
Class Holothuroidea
• Sea cucumbers belong to the class Holothuroidea.
• Holothuroidea means “water polyp.”
• Most of these armless echinoderms live on the sea
bottom, where they crawl or burrow into soft sediment
by using their tube feet.
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Chapter 38
Section 1 Echinoderms
Classification, continued
Class Asteroidea
• The sea stars, or starfish, belong to the class
Asteroidea, which means “starlike.”
• Sea stars are economically important because they
prey on oysters, clams, and other organisms that
humans use as food.
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Chapter 38
Section 1 Echinoderms
Structure and Function of Echinoderms
External Structure
• The body of a sea star is composed of several arms
that extend from a central region. Two rows of tube
feet run along the underside of each arm.
• The side of the body where the mouth is located is
referred to as the oral surface. The opposite side is
called the aboral surface.
• The body of a sea star is usually covered with short
spines. Surrounding each spine in many sea stars
are numerous tiny pincers called pedicellariae.
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Chapter 38
Section 1 Echinoderms
Structure and Function of Echinoderms,
continued
Water-Vascular System
• The water-vascular system is a network of water-filled
canals that are connected to the tube feet.
• This coordinated system enables sea stars to climb
slippery rocks and capture prey.
• Water enters through the madreporite, passes down
the stone canal to the ring canal, then through the
radial canal to the end of each arm and to the tube
feet.
• The upper end of each tube foot is a bulblike sac called
an ampulla.
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Chapter 38
Section 1 Echinoderms
Structure and Function of Echinoderms,
continued
Feeding and Digestion
• The sea star can turn its cardiac stomach inside out
through its mouth when it feeds.
• The cardiac stomach transfers food to the pyloric
stomach, which connects to a pair of digestive
glands in each arm.
• Most sea stars are carnivorous.
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Chapter 38
Section 1 Echinoderms
Structure and Function of Echinoderms,
continued
Other Body Systems
• Like other echinoderms, the sea star has no
circulatory, excretory, or respiratory organ systems.
• The nervous system consists mainly of a nerve ring
and a radial nerve that runs along each arm.
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Chapter 38
Section 1 Echinoderms
Structure and Function of Echinoderms,
continued
Reproduction and Development
• Most echinoderms have separate sexes.
• Each arm of the sea star contains a pair of ovaries or
testes.
• Fertilization occurs externally in water.
• Each fertilized egg develops into a bilaterally
symmetrical, free-swimming larva called a bipinnaria.
• Echinoderms have remarkable powers of regeneration.
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Chapter 38
Section 1 Echinoderms
Anatomy of
a Sea Star
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Chapter 38
Section 1 Echinoderms
Characteristics of Echinoderms
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Chapter 38
Section 1 Echinoderms
Pentaradial Symmetry
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Chapter 38
Section 1 Echinoderms
Water Vascular System
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Chapter 38
Section 1 Echinoderms
Anatomy of a Sea Star
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Chapter 38
Section 1 Echinoderms
Types of Echinoderms
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Chapter 38
Section 2 Invertebrate Chordates
Objectives
• List the major characteristics of chordates.
• Describe the evolution and classification of
invertebrate chordates.
• Describe the structure of lancelets.
• Describe the structure of tunicates.
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Chapter 38
Section 2 Invertebrate Chordates
Characteristics
• Chordates, phylum Chordata, are characterized by
having a notochord.
• In most vertebrates, the notochord is present in
embryos but reduced in adults.
• In addition, all chordates have the following
characteristics during some stage of their life:
– a dorsal nerve cord
– pharyngeal pouches
– a postanal tail
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Chapter 38
Section 2 Invertebrate Chordates
Evolution and Classification
• Echinoderms and chordates likely evolved from a
common ancestor.
• The phylum Chordata is divided into three subphyla:
– Vertebrata
– Cephalochordata
– Urochordata
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Chapter 38
Section 2 Invertebrate Chordates
Evolution and Classification, continued
Subphylum Cephalochordata
• The subphylum Cephalochordata contains about two
dozen species of lancelets.
• Lancelets retain their notochord, dorsal nerve cord,
pharyngeal pouches, and postanal tail throughout
their life.
• Lancelets feed by filtering water through the slits in
the pharynx. The water leaves the body through the
atriopore.
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Chapter 38
Section 2 Invertebrate Chordates
Evolution and Classification, continued
Subphylum Urochordata
• The subphylum Urochordata contains about 2,000
species commonly called tunicates or sea squirts.
• As adults, most tunicates are sessile, barrel-shaped
filter feeders that live on the sea bottom. They may
be solitary or colonial.
• Tunicates are hermaphrodites.
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Chapter 38
Section 2 Invertebrate Chordates
Lancelet Interior
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Chapter 38
Section 2 Invertebrate Chordates
Exploration of a Lancelet
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Chapter 38
Section 2 Invertebrate Chordates
Adult Tunicate
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Chapter 38
Section 2 Invertebrate Chordates
Characteristics of Invertebrate Chordates
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Chapter 38
Section 2 Invertebrate Chordates
Parts of a Chordate
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Chapter 38
Section 2 Invertebrate Chordates
Anatomy of a Lancelet
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Chapter 38
Section 2 Invertebrate Chordates
Anatomy of a Tunicate
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Chapter 38
Standardized Test Prep
Multiple Choice
1. In a sea star, gas exchange and excretion of wastes
take place by diffusion through which of the following
structures?
A. pharynx
B. skin gills
C. atriopore
D. radial canals
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
1. In a sea star, gas exchange and excretion of wastes
take place by diffusion through which of the following
structures?
A. pharynx
B. skin gills
C. atriopore
D. radial canals
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
2. Which of the following types of symmetry is
characteristic of echinoderms?
F. biradial
G. bilateral
H. pentaradial
J. pentalateral
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
2. Which of the following types of symmetry is
characteristic of echinoderms?
F. biradial
G. bilateral
H. pentaradial
J. pentalateral
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
3. Which of the following classes of echinoderms most
closely resembles the fossils of ancient
echinoderms?
A. Crinoidea
B. Asteroidea
C. Echinoidea
D. Holothuroidea
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
3. Which of the following classes of echinoderms most
closely resembles the fossils of ancient
echinoderms?
A. Crinoidea
B. Asteroidea
C. Echinoidea
D. Holothuroidea
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
4. Which of the following is found in adult tunicates, or
sea squirts?
F. eyespot
G. notochord
H. spinal cord
J. pharynx with slits
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
4. Which of the following is found in adult tunicates, or
sea squirts?
F. eyespot
G. notochord
H. spinal cord
J. pharynx with slits
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
The illustration below shows a sea star and a sand dollar.
Use the illustration to answer the question that follows.
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
5. To which phylum do these animals belong?
A. Chordata
B. Vertebrata
C. Arthropoda
D. Echinodermata
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
5. To which phylum do these animals belong?
A. Chordata
B. Vertebrata
C. Arthropoda
D. Echinodermata
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
6. Cardiac stomach : digestion :: atriopore :
F. excretion
G. respiration
H. circulation
J. reproduction
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
6. Cardiac stomach : digestion :: atriopore :
F. excretion
G. respiration
H. circulation
J. reproduction
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
The diagram below shows a lancelet. Use the diagram
to answer the question that follows.
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
7. Which four structures are the main distinguishing
characteristics of chordates?
A. 1, 2, 3, 4
B. 1, 2, 3, 8
C. 2, 3, 4, 6
D. 2, 3, 4, 9
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Chapter 38
Standardized Test Prep
Multiple Choice, continued
7. Which four structures are the main distinguishing
characteristics of chordates?
A. 1, 2, 3, 4
B. 1, 2, 3, 8
C. 2, 3, 4, 6
D. 2, 3, 4, 9
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Chapter 38
Standardized Test Prep
Short Response
Echinoderms and chordates are believed to have
evolved from a common ancestor.
Describe the evidence that supports this view.
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Chapter 38
Standardized Test Prep
Short Response, continued
Echinoderms and chordates are believed to have
evolved from a common ancestor.
Describe the evidence that supports this view.
Answer: Because both echinoderms and chordates are
deuterostomes and all other invertebrates are
protostomes it is believed that they descended from
the same ancestor.
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Chapter 38
Standardized Test Prep
Extended Response
The fossil record of echinoderms dates to the
Cambrian period, more than 500 million years ago.
Scientists have observed many well-preserved
echinoderm species from this period.
Part A
Based on the fossil evidence, which
characteristics did the earliest adult echinoderms
have, in terms of symmetry and ability to move?
Part B
Based on your answer to Part A, describe the
evolution of echinoderms.
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Chapter 38
Standardized Test Prep
Extended Response, continued
Answers
Part A
They were bilaterally symmetrical and sessile.
Part B
Present-day echinoderms are radially symmetrical and may
move about. Echinoderms probably evolved radial symmetry
as an adaptation to their sessile existence. Later, they
evolved mobility. Over time, mobile species became more
numerous , and today most species can move about. It is
unlikely that echinoderms evolved mobility and then radial
symmetry, because there would be no selective pressure for
radial symmetry in a species that was mobile.
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