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Chapter 31
Echinoderms and Invertebrate
Chordates
Table of Contents
Section 1 Echinoderms
Section 2 Invertebrate Chordates
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Chapter 31
Section 1 Echinoderms
Objectives
• Compare the developmental pattern found in
protostomes with that found in deuterostomes.
• Describe the major characteristics of echinoderms.
• Summarize how the sea star’s water vascular
system functions.
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Chapter 31
Section 1 Echinoderms
Animal Development
• As an embryo develops, it goes through a gastrula
stage. A gastrula has an opening to the outside called
the blastopore.
• Animals with mouths that develop from or near the
blastopore are called protostomes.
• In phylums Echinodermata and Chordata, the anus—
not the mouth—develops from or near the blastopore.
(The mouth forms later, on another part of the
embryo.) Animals with this pattern of development
are called deuterostomes.
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Chapter 31
Section 1 Echinoderms
Patterns of Embryonic Development
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Chapter 31
Section 1 Echinoderms
Animal Development, continued
• The first deuterostomes were marine echinoderms
that evolved more than 650 million years ago. They
were also the first animals to develop an
endoskeleton.
• Like the echinoderms, chordates have an internal
skeleton. This developmental similarity unites these
seemingly dissimilar animal phyla.
• The identity of the ancestral deuterostome is not
known.
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Chapter 31
Section 1 Echinoderms
Animal Development, continued
This phylogenetic tree shows the relationship of the
major chordate and echinoderm groups.
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Chapter 31
Section 1 Echinoderms
Characteristics of Echinoderms
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Chapter 31
Section 1 Echinoderms
Modern Echinoderms
• Many of the most familiar animals seen along the
seashore—sea stars, sea urchins, sand dollars—are
echinoderms.
• Echinoderms have a calcium-rich endoskeleton
composed of individual plates called ossicles.
• All echinoderms are bilaterally symmetrical as larvae.
During their development into adults, the larvae’s
body plan becomes radially symmetrical.
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Chapter 31
Section 1 Echinoderms
Pentaradial Symmetry
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Chapter 31
Section 1 Echinoderms
Modern Echinoderms, continued
• Echinoderms have a waterfilled system of
interconnected canals and thousands of tiny hollow
tube feet called a water-vascular system.
• The echinoderm body cavity functions as a simple
circulatory and respiratory system.
• Skin gills are small, fingerlike projections that grow
among the echinoderm’s spines. These projections
create an increased surface area through which
respiratory gases can be exchanged.
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Chapter 31
Section 1 Echinoderms
Water Vascular System
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Chapter 31
Section 1 Echinoderms
Anatomy of a Sea Star
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Chapter 31
Section 1 Echinoderms
Anatomy of a Sea Star
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Chapter 31
Section 1 Echinoderms
Types of Echinoderms
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Chapter 31
Section 1 Echinoderms
Echinoderm Diversity
Sea Stars
• Almost all species of sea stars are carnivores, and
they are among the most important predators in
many marine ecosystems.
• The ossicles of many species of sea stars produce
pincerlike structures called pedicellaria.
• Pedicellaria contain their own muscles and nerves,
and they snap at anything that touches them. This
action prevents small organisms from attaching
themselves to the surface of the sea star.
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Chapter 31
Section 1 Echinoderms
Echinoderm Diversity, continued
Brittle Stars
• The sea star’s relatives, the brittle stars and sea
baskets, make up the largest class of echinoderms.
• Brittle stars have slender branched arms that they
move in pairs to row along the ocean floor.
• Although a few species are predators, most brittle
stars are filter feeders or feed on food in the ocean
sediment.
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Chapter 31
Section 1 Echinoderms
Echinoderm Diversity, continued
Sea Lilies and Feather Stars
• The sea lilies and feather stars are the most
ancient and primitive living echinoderms.
• They differ from all other living echinoderms
because their mouth is located on their upper,
rather than lower, surface.
• Sea lilies are sessile and are attached to the
ocean floor by a stalk. Feather stars use hooklike
projections to attach themselves directly to the
ocean bottom or a coral reef.
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Chapter 31
Section 1 Echinoderms
Echinoderm Diversity, continued
Sea Urchins and Sand Dollars
• The sea urchins and sand dollars lack distinct
arms but have the basic five-part body plan seen
in other echinoderms.
• Both sea urchins and sand dollars have a hard,
somewhat flattened endoskeleton of fused plates
covered with spines protruding from it.
• Sea urchins are found on the ocean bottoms
while sand dollars live in sandy areas along the
sea coast.
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Chapter 31
Section 1 Echinoderms
Echinoderm Diversity, continued
Sea Cucumbers
• Sea cucumbers are soft-bodied, sluglike animals
without arms. They differ from other echinoderms in
that their ossicles are small and are not fused
together.
• The sexes of most sea cucumbers are separate, but
some species are hermaphrodites.
• Sea cucumbers feed by trapping tiny organisms
present in the sea water. Their mouth is surrounded
by several dozen tube feet modified into tentacles.
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Chapter 31
Section 1 Echinoderms
Echinoderm Diversity, continued
Sea Daisies
• In 1986, a new class of echinoderm was discovered:
strange diskshaped little animals called sea daisies.
• Sea daisies have five-part radial symmetry but no
arms.
• Their tube feet are located around the edges of the
disk rather than along the radial lines, like they are in
other echinoderms.
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Chapter 31
Section 2 Invertebrate Chordates
Objectives
• Describe the characteristics of chordates.
• Define the term invertebrate chordate.
• Compare tunicates and lancelets.
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Chapter 31
Section 2 Invertebrate Chordates
The Chordate Skeleton
• The second major group of deuterostomes are the
chordates. Chordates have a very different kind of
endoskeleton from that of echinoderms.
• During the development of the chordate embryo, a
stiff rod called the notochord develops along the
back of the embryo.
• Using muscles attached to this rod, early chordates
could swing their backs from side to side, enabling
them to swim through the water.
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Chapter 31
Section 2 Invertebrate Chordates
The Chordate Skeleton, continued
Other Chordate Characteristics
• Chordates have a single, hollow, dorsal nerve cord
with nerves attached to it that travel to different parts
of the body.
• Chordates also have a series of pharyngeal
pouches that develop in the wall of the pharynx, the
muscular tube that connects the mouth to the
digestive tract and windpipe.
• Another chordate characteristic is a postanal tail,
which is a tail that extends beyond the anus.
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Chapter 31
Section 2 Invertebrate Chordates
Parts of a Chordate
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Chapter 31
Section 2 Invertebrate Chordates
Lancelet Interior
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Chapter 31
Section 2 Invertebrate Chordates
Anatomy of a Lancelet
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Chapter 31
Section 2 Invertebrate Chordates
Invertebrate Chordates
• The vast majority of chordate species belong to
subphylum Vertebrata.
• Two other subphyla, Urochordata (the tunicates) and
Cephalochordata (the lancelets), contain a small
number of species.
• Because members of these two subphyla are
chordates that do not have backbones, they are
called invertebrate chordates.
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Chapter 31
Section 2 Invertebrate Chordates
Characteristics of Invertebrate Chordates
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Chapter 31
Section 2 Invertebrate Chordates
Invertebrate Chordates, continued
Tunicates
• Most adult tunicates are sessile, filter-feeding
marine animals. A tough sac, called a tunic,
develops around the adult’s body and gives
tunicates their name.
• Cilia beating within the tunicate cause water to
enter the incurrent siphon. As water passes
through the slits in the pharynx, food is filtered
from it and passed into the stomach.
• All tunicates are hermaphrodites, and some are
also able to reproduce asexually by budding.
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Chapter 31
Section 2 Invertebrate Chordates
Adult Tunicate
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Chapter 31
Section 2 Invertebrate Chordates
Anatomy of a Tunicate
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Chapter 31
Section 2 Invertebrate Chordates
Invertebrate Chordates, continued
Lancelets
• Lancelets receive their name from their bladelike
shape. Although lancelets may resemble fish, they
are not fish.
• The lancelets V-shaped bundles of muscles are
arranged in a series of repeating segments.
• Lancelets feed on microscopic protists that they filter
out of the water. Unlike tunicates, the sexes are
separate in lancelets.
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Chapter 31
Standardized Test Prep
Multiple Choice
The diagram below shows a vertical cross section of
an adult tunicate. Use the diagram to answer
questions 1–3.
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Chapter 31
Standardized Test Prep
Multiple Choice, continued
1. This organism is in the same phylum as
A.
B.
C.
D.
sea anemones.
sea cucumbers.
sponges.
humans.
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Chapter 31
Standardized Test Prep
Multiple Choice, continued
1. This organism is in the same phylum as
A.
B.
C.
D.
sea anemones.
sea cucumbers.
sponges.
humans.
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Chapter 31
Standardized Test Prep
Multiple Choice, continued
2. Which chordate characteristic does this organism
have as an adult?
F.
G.
H.
J.
pharyngeal slits
dorsal nerve cord
notochord
postanal tail
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Chapter 31
Standardized Test Prep
Multiple Choice, continued
2. Which chordate characteristic does this organism
have as an adult?
F.
G.
H.
J.
pharyngeal slits
dorsal nerve cord
notochord
postanal tail
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Chapter 31
Standardized Test Prep
Multiple Choice, continued
3. What is the significance of the relationship between
structures A and B?
A. B releases undigested food into the water that
leaves the body through A.
B. B releases gametes into the water that leaves
the body through A.
C. B collects food from the water that enters the
body through A.
D. B extracts oxygen from the water that enters the
body through A.
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Chapter 31
Standardized Test Prep
Multiple Choice, continued
3. What is the significance of the relationship between
structures A and B?
A. B releases undigested food into the water that
leaves the body through A.
B. B releases gametes into the water that leaves
the body through A.
C. B collects food from the water that enters the
body through A.
D. B extracts oxygen from the water that enters the
body through A.
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