Unit 1: What is Biology?
Unit 2: Ecology
Unit 3: The Life of a Cell
Unit 4: Genetics
Unit 5: Change Through Time
Unit 6: Viruses, Bacteria, Protists, and Fungi
Unit 7: Plants
Unit 8: Invertebrates
Unit 9: Vertebrates
Unit 10: The Human Body
Unit 1: What is Biology?
Chapter 1: Biology: The Study of Life
Unit 2: Ecology
Chapter 2: Principles of Ecology
Chapter 3: Communities and Biomes
Chapter 4: Population Biology
Chapter 5: Biological Diversity and Conservation
Unit 3: The Life of a Cell
Chapter 6: The Chemistry of Life
Chapter 7: A View of the Cell
Chapter 8: Cellular Transport and the Cell Cycle
Chapter 9: Energy in a Cell
Unit 4: Genetics
Chapter 10: Mendel and Meiosis
Chapter 11: DNA and Genes
Chapter 12: Patterns of Heredity and Human Genetics
Chapter 13: Genetic Technology
Unit 5: Change Through Time
Chapter 14: The History of Life
Chapter 15: The Theory of Evolution
Chapter 16: Primate Evolution
Chapter 17: Organizing Life’s Diversity
Unit 6: Viruses, Bacteria, Protists, and Fungi
Chapter 18: Viruses and Bacteria
Chapter 19: Protists
Chapter 20: Fungi
Unit 7: Plants
Chapter 21:
Chapter 22:
Chapter 23:
Chapter 24:
What Is a Plant?
The Diversity of Plants
Plant Structure and Function
Reproduction in Plants
Unit 8: Invertebrates
Chapter 25: What Is an Animal?
Chapter 26: Sponges, Cnidarians, Flatworms, and
Roundworms
Chapter 27: Mollusks and Segmented Worms
Chapter 28: Arthropods
Chapter 29: Echinoderms and Invertebrate Chordates
Unit 9: Vertebrates
Chapter 30: Fishes and Amphibians
Chapter 31: Reptiles and Birds
Chapter 32: Mammals
Chapter 33: Animal Behavior
Unit 10: The Human Body
Chapter 34: Protection, Support, and Locomotion
Chapter 35: The Digestive and Endocrine Systems
Chapter 36: The Nervous System
Chapter 37: Respiration, Circulation, and Excretion
Chapter 38: Reproduction and Development
Chapter 39: Immunity from Disease
Invertebrates
What is an animal?
Sponges, Cnidarians, Flatworms and
Roundworms
Mollusks and Segmented Worms
Arthropods
Echinoderms and Invertebrate Chordates
Chapter 29 Echinoderms and Invertebrate
Chordates
29.1: Echinoderms
29.1: Section Check
29.2: Invertebrate Chordates
29.2: Section Check
Chapter 29 Summary
Chapter 29 Assessment
What You’ll Learn
You will compare and contrast the
adaptations of echinoderms.
You will distinguish the features of
chordates by examining invertebrate
chordates.
Section Objectives:
• Compare similarities and differences among
the classes of echinoderms.
• Interpret the evidence biologists have for
determining that echinoderms are close
relatives of chordates.
What is an echinoderm?
• Echinoderms move by means of hundreds of
hydraulic, suction-cup-tipped appendages
and have skin covered with tiny, jawlike
pincers.
• Echinoderms are
found in all the
oceans of the world.
Echinoderms have endoskeletons
• If you were to examine the skin of several
different echinoderms, you would find that
they all have a hard, spiny,or bumpy
endoskeleton covered by a thin epidermis.
Echinoderms have endoskeletons
• Sea stars, sometimes called starfishes, may
not appear spiny at first glance, but a close
look reveals that their long, tapering arms,
called rays, are covered with short, rounded
spines.
• The endoskeleton of all echinoderms is
made primarily of calcium carbonate, the
compound that makes up limestone.
Echinoderms have endoskeletons
• Some of the spines found on sea stars and
sea urchins have become modified into
pincerlike appendages called pedicellariae
(PEH dih sih LAHR ee ay).
Echinoderms have endoskeletons
• An echinoderm
uses its jawlike
pedicellariae
for protection
and for
cleaning the
surface of its
body.
Pedicellariae
Echinoderms have radial symmetry
• You may remember that radial symmetry is
an advantage to animals that are stationary
or move slowly.
• Radial symmetry
enables these animals
to sense potential food,
predators, and other
aspects of their
environment from all
directions.
The water vascular system
• The water vascular system is a hydraulic
system that operates under water pressure.
• Water enters and leaves the water vascular
system of a sea star through the madreporite
(mah druh POHR ite), a sievelike, diskshaped opening on the upper surface of the
echinoderm’s body.
The water vascular system
• The underside of a sea star has tube feet that
run along a groove on the underside of each
ray.
The water vascular system
• Tube feet are hollow, thin-walled tubes that
end in a suction cup.
• Tube feet look somewhat like miniature
droppers.
• The round, muscular structure called the
ampulla (AM pew lah) works something like
the bulb of a dropper.
The water vascular system
• Each tube foot
works
independently of
the others, and the
animal moves along
slowly by
alternately pushing
out and pulling in
its tube feet.
Ampullae
The water vascular system
• Tube feet also function in gas exchange and
excretion. Gases are exchanged and wastes
are eliminated by diffusion through the thin
walls of the tube feet.
Echinoderms have varied nutrition
• All echinoderms have a mouth, stomach,
and intestines, but their methods of
obtaining food vary.
• Sea stars are carnivorous and prey on
worms or on mollusks such as clams.
Echinoderms have varied nutrition
• Most sea urchins are herbivores and graze
on algae.
• Brittle stars, sea lilies, and sea cucumbers
feed on dead and decaying matter that drifts
down to the ocean floor.
Echinoderms have a simple nervous
system
• Echinoderms
have no head or
brain, but they
do have a central
nerve ring that
surrounds the
mouth.
Ring
canal
Echinoderms have a simple nervous
system
• Nerves extend from the nerve ring down
each ray.
• Each radial nerve then branches into a nerve
net that provides sensory information to the
animal.
• Echinoderms have cells that detect light and
touch, but most do not have sensory organs.
Echinoderms have a simple nervous
system
• Sea stars are an exception. A sea star’s body
consists of long, tapering rays that extend
from the animal’s central disk.
• A sensory organ known as an eyespot and
consisting of a cluster of light-detecting cells
is located at the tip of each arm, on the
underside.
Echinoderms have a simple nervous
system
• Eyespots enable sea stars to detect the
intensity of light.
• Sea stars also have chemical receptors on
their tube feet.
Echinoderms have bilaterally
symmetrical larvae
• If you examine the larval stages of
echinoderms, you will find that they have
bilateral symmetry.
• Through metamorphosis, the free-swimming
larvae make dramatic changes in both body
parts and in symmetry.
Echinoderms are deuterostomes
• Echinoderms are deuterostomes.
• This pattern of development indicates a
close relationship to chordates, which are
also deuterostomes.
Diversity of Echinoderms
• Approximately 6000 species of echinoderms
exist today.
• About one-fourth
of these species
are in the class
Asteroidea (AS
tuh ROY dee uh),
to which the sea
stars belong.
Diversity of Echinoderms
• The five other classes of living echinodems
are Ophiuroidea (OH fee uh ROY dee uh),
the brittle stars; Echinoidea (eh kihn OY
dee uh), the sea urchins and sand dollars.
Diversity of Echinoderms
• Holothuroidea (HOH loh thuh ROY dee uh),
the sea cucumbers; Crinoidea (cry NOY dee
uh), the sea lilies and feather stars; and
Concentricycloidea (kon sen tri sy CLOY
dee uh), the sea daisies.
Sea Cucumber
Sea stars
• Most species of sea stars have five rays, but
some have more. Some species may have
more than 40 rays.
Sea stars
Pedicellariae
Endoskeleton
Ray
Madreporite
Radial
canal
Radial
nerve
Tube feet
Eyespots
Anus
Ring
canal
Ampullae
Nerve ring
Stomach
Mouth
Reproductive
organ
Endoskeletal
plates
Digestive
gland
Brittle stars
• Brittle stars are extremely fragile.
• This adaptation helps the brittle star survive
an attack by a predator.
• While the predator is busy with the broken
off ray, the brittle star can escape. A new ray
will regenerate.
Brittle stars
• Brittle stars propel themselves with the
snake like, slithering motion of their flexible
rays.
• They use their tube
feet to pass
particles of food
along the rays and
into the mouth in
the central disk.
Sea urchins and sand dollars
• Sea urchins and sand dollars are globe or
disk-shaped animals covered with spines;
they do not have rays.
• A living sand dollar is covered with minute,
hair-like spines that are lost when the animal
dies.
• A sand dollar has tube feet that protrude
from the petal-like markings on its upper
surface.
Sea urchins and sand dollars
• These tube feet are modified into gills and
are used for respiration.
• Tube feet on the
animal’s bottom
surface aid in
bringing food
particles to the
mouth.
Sea urchins and sand dollars
• Sea urchins look like living pincushions,
bristling with long, usually pointed spines.
• Sea urchins have
long, slender tube
feet that, along with
the spines, aid the
animal in
locomotion.
Sea cucumbers
• Sea cucumbers are so called because of their
vegetable-like appearance.
• Their leathery covering allows them
flexibility as they move along the ocean
floor.
Sea cucumbers
• When sea cucumbers are threatened, they
may expel a tangled, sticky mass of tubes
through the anus, or they may rupture,
releasing some internal organs that are
regenerated in a few weeks.
• Sea cucumbers reproduce by shedding eggs
and sperm into the water, where fertilization
occurs.
Sea lilies and feather stars
• Sea lilies and feather stars resemble plants in
some ways.
• Sea lilies are the only sessile echinoderms.
• Feather stars are sessile only in larval form.
The adult feather star uses its feathery arms
to swim from place to place.
Sea daisies
• Sea daisies are flat, disk-shaped animals less
than 1 cm in diameter.
• Their tube feet are located around the edge
of the disk rather than along radial lines, as
in other echinoderms.
Origins of Echinoderms
• The earliest echinoderms may have been
bilaterally symmetrical as adults, and
probably were attached to the ocean floor by
stalks.
• Another view of the earliest echinoderms is
that they were bilateral and free swimming.
Origins of Echinoderms
• The echinoderms represent the only major
group of deuterostome invertebrates.
• This pattern of development is one piece of
evidence biologists have for placing
echinoderms as the closest invertebrate
relatives of the chordates.
Origins of Echinoderms
• Most echinoderms have been found as
fossils from the early Paleozoic Era.
• Fossils of brittle
stars are found
beginning at a
later period.
Not much is
known about
the origin of sea
daisies.
Question 1
Why is radial symmetry an advantage
to animals that are stationary or slow
moving?
(TX Obj 2;
8C)
Radial symmetry enables stationary or
slow moving animals to sense potential
food, predators, and other aspects of
their environment from all directions.
Question 2
What is the similarity between the
endoskeleton of echinoderms and the
exoskeleton of crustaceans? (TX Obj 2;
8C, 10A, 10B)
Answer
Both of these features are composed
of calcium carbonate.
Question 3
Pincerlike appendages from modified
spines on sea stars are called _______.
(TX Obj 2; 8C, 10A, 10B)
A. rays
B. pedicellariae
C. madreporites
D. tube feet
The answer is B, pedicellariae.
Pedicellariae
Question 4
Which of the following terms does NOT
describe an echinoderm’s method of
obtaining food? TX Obj 2; 8C, 10A, 10B
TX Obj 3; 12B, 12E)
A. carnivore
B. herbivore
C. parasite
D. scavenger
The answer is C, parasite.
Question 5
What stimulates a sea star to move in a
given direction?
(TX Obj 2; 8C, 10A, 10B)
Sea stars move toward light and toward
chemical signals emitted from potential
prey animals.
Section Objectives:
• Summarize the characteristics of chordates.
• Explain how invertebrate chordates are
related to vertebrates.
• Distinguish between sea squirts and
lancelets.
What is an invertebrate chordate?
• The phylum Chordata includes three
subphyla: Urochordata, the tunicates (sea
squirts); Cephalochordata, the lancelets;
and Vertebrata, the vertebrates.
• Invertebrate chordates have a notochord, a
dorsal hollow nerve cord, pharyngeal
pouches, and a postanal tail at some time
during their development.
What is an invertebrate chordate?
• In addition, all chordates have bilateral
symmetry, a well-developed coelom, and
segmentation.
Dorsal hollow
nerve cord
Mouth
Notochord
Pharyngeal
pouches
Anus Postanal
tail
Muscle
blocks
All chordates have a notochord
• The embryos of all
chordates have a
notochord (NOH
tuh kord) — a long,
semirigid, rod-like
structure located
between the
digestive system
and the dorsal
hollow nerve cord.
Nerve cord
Gill slits
Notochord
All chordates have a notochord
• In invertebrate chordates, the notochord may
be retained into adulthood. But in vertebrate
chordates, this structure is replaced by a
backbone.
• Invertebrate chordates do not develop a
backbone.
All chordates have a notochord
• The notochord develops just after the
formation of a gastrula from mesoderm on
what will be the dorsal side of the embryo.
• The notochord anchors internal muscles and
enables invertebrate chordates to make rapid
movements of the body.
All chordates have a dorsal hollow
nerve cord
• The dorsal hollow nerve cord in chordates
develops from a plate of ectoderm that rolls
into a hollow tube.
Outer layer of
ectoderm
Dorsal hollow
nerve cord
All chordates have a dorsal hollow
nerve cord
• This tube is composed of cells surrounding a
fluid-filled canal that lies above the
notochord.
• In most adult chordates, the cells in the
posterior portion of the dorsal hollow nerve
cord develop into the spinal cord.
All chordates have a dorsal hollow
Neural Neural
nerve cord
fold
plate
• The cells in the Neural foldNeural plate
anterior portion
Notochord
Ectoderm
develop into a
Mesoderm
Endoderm
Outer layer
brain.
of ectoderm
Dorsal hollow
nerve cord
Dorsal hollow
• A pair of
nerve cord
Cells that
nerves connects
form bones
and muscles
the nerve cord
to each block Notochord
Dorsal hollow
of muscles.
nerve cord
All chordates have pharyngeal pouches
• The pharyngeal pouches of a chordate
embryo are paired openings located in the
pharynx, behind the mouth.
• In aquatic chordates, pharyngeal pouches
develop openings called gill slits.
• In terrestrial chordates, pharyngeal pouches
develop into other structures.
All chordates have a postanal tail
• At some point in
development, all
chordates have a
postanal tail.
Postanal tail
• Humans are
chordates, and
during the early
development of the
human embryo,
there is a postanal
tail that disappears
as development
continues.
All chordates have a postanal tail
• In most animals that have
tails, the digestive system
extends to the tip of the
tail, where the anus is
located.
• Chordates, however,
usually have a tail that
extends beyond the
anus.
All chordates have a postanal tail
• Muscle blocks aid in movement of the tail.
• Muscle blocks are modified body segments
that consist of stacked muscle layers.
• Muscle blocks are anchored by the
notochord, which gives the muscles a firm
structure to pull against.
Homeotic genes control development
• Homeotic genes specify body organization
and direct the development of tissues and
organs in an embryo.
• Studies of chordate homeotic genes have
helped scientists understand the process of
development and the relationship of
invertebrate chordates to vertebrate
chordates.
Diversity of Invertebrate Chordates
• The invertebrate chordates belong to two
subphyla of the phylum chordata: subphylum
Urochordata, the tunicates (TEW nuh kaytz),
also called sea squirts, and subphylum
Cephalochordata, the lancelets.
Tunicates are sea squirts
• Although adult tunicates do not appear to
have any shared chordate features, the larval
stage, has a tail that makes it look similar to
a tadpole.
Tunicates are sea squirts
• Tunicate larvae do not feed and are free
swimming after hatching.
• They soon settle and attach themselves with
a sucker to boats, rocks, and the ocean
bottom.
• Many adult tunicates secrete a tunic, a tough
sac made of cellulose, around their bodies.
Tunicates are sea squirts
• Colonies of tunicates sometimes secrete just
one big tunic that has a common opening to
the outside.
• Only the gill slits in adult tunicates indicate
their chordate relationship.
• Adult tunicates are small, tubular animals
that range in size from microscopic to
several centi-meters long.
Tunicates are sea squirts
• If you remove a tunicate from its sea home,
it might squirt out a jet of water-hence the
name sea squirt.
Water
A Tunicate
Incurrent siphon
Excurrent siphon
Mouth
Ciliated groove
Pharynx
Anus
Gill slits
Heart
Reproductive
organs
Intestine
Tunic
Esophagus
Stomach
Lancelets are similar to fishes
• Lancelets are small, streamlined, and
common marine animals, usually about 5 cm
long.
• Like tunicates, lancelets are filter feeders.
Lancelets are similar to fishes
• Unlike tunicates, however, lancelets retain
all their chordate features throughout life.
Oral hood with tentacles
Dorsal hollow
nerve cord
Postanal tail
Notochord
Muscle blocks
Anus
Intestine
Mouth
Gill slits in
pharynx
Lancelets are similar to fishes
• Although lancelets look somewhat similar to
fishes, they have only one layer of skin, with
no pigment and no scales.
Lancelets are similar to fishes
• Lancelets do not have a distinct head, but
they do have light sensitive cells on the
anterior end.
• They also have a hood that covers the mouth
and the sensory tentacles surrounding it.
• The tentacles direct the water current and
food particles toward the animal’s mouth.
Origins of Invertebrate Chordates
• Biologist are not sure where sea squirts and
lancelets fit in the phylogeny of chordates.
• According to one hypothesis, echinoderms,
invertebrate chordates, and vertebrates all
arose from ancestral sessile animals that fed
by capturing food in tentacles.
Origins of Invertebrate Chordates
• Recent discoveries of fossil forms of
organisms that are similar to living lancelets
in rocks 550 million years old show that
invertebrate chordates probably existed
before vertebrate chordates.
Question 1
Which of the following features is NOT shared
by all chordates? (TX Obj 2; 8C, 10A, 10B)
A. bilateral symmetry
B. coelom
C. segmentation
D. protostome development
The answer is D, protostome development.
Question 2
In vertebrates the notochord is replaced by
the _______. (TX Obj 2; 8C, 10A, 10B)
A. backbone
B. brain
C. spinal chord
D. medulla
The answer is A, backbone.
Question 3
How does a notochord aid in the
movement of a chordate?
(TX Obj 2; 8C, 10A, 10B)
The notochord anchors internal muscles and
enables invertebrate chordates to make rapid
movements of the body, which they use to
propel themselves.
Dorsal hollow
nerve cord
Mouth
Notochord
Pharyngeal
pouches
Anus Postanal
tail
Muscle
blocks
Question 4
How is a tunicate heart unusual?
(TX Obj 2; 8C, 10A, 10B)
The tunicate
heart pumps
blood in one
direction for
several
minutes and
then reverses
direction.
Heart
Question 5
What is the only feature of adult tunicates
that indicates their chordate relationship?
(TX Obj 2; 8C, 10A, 10B)
A. notochord
B. gill slits
C. postanal tail
D. dorsal hollow nerve cord
The answer is B,
gill slits.
Gill slits
Echinoderms
• Echinoderms have spines or bumps on their
endoskeletons, radial symmetry, and water
vascular systems. Most move by means of
the suction action of tube feet.
• Echinoderms can be carnivorous,
herbivorous, scavengers, or filter feeders.
• Echinoderms include sea stars, brittle stars,
sea urchins, sand dollars, sea cucumbers,
sea lilies, feather stars, and sea daisies.
Echinoderms
• Deuterostome development is an indicator of
the close phylogenetic relationship between
echinoderms and chordates.
• A good fossil record of this phylum exists
because the endoskeleton of echinoderms
fossilizes easily.
Invertebrate Chordates
• All chordates have a dorsal hollow nerve cord,
a notochord, pharyngeal pouches, and a
postanal tail at some stage during
development.
• All chordates also have bilateral symmetry, a
well-developed coelem, and segmentation.
Invertebrate Chordates
• Sea squirts and lancelets are invertebrate
chordates.
• Vertebrate chordates may have evolved from
larval stages of ancestral invertebrate
chordates.
Question 1
Which of the following is not a function
of tube feet? (TX Obj 2; 8C, 10A, 10B)
A. digestion
B. excretion
C. gas exchange
D. movement
The answer is A, digestion.
Tube feet
Question 2
What is the difference in the way sea stars
and brittle stars use their tube feet?
(TX Obj 2; 8C, 10A, 10B)
Sea stars use their tube feet to move. Brittle
stars use their feet to pass particles of food
along their rays and into their mouth.
Question 3
The only sessile echinoderms belong to the
_______. (TX Obj 2; 8C, 10A, 10B)
A. Asteroidea
B. Ophiuroidea
C. Echinoidea
D. Crinoidea
The answer is D. The Crinoidea include the
sea lilies which are sessile.
Question 4
Describe the sea cucumber’s method of
protection from predators. TX Obj 2; 8C,
10A, 10B)
When sea cucumbers are threatened they
may expel portions of themselves through the
anus or a ruptured part of the skin to confuse
predators. The expelled portions are
regenerated later.
Question 5
What is the adaptive value of colonies of sea
cucumbers all shedding eggs and sperm into
the water at the same time?
(TX Obj 2; 8C, 10A, 10B )
Answer
The adaptive value of this behavior is that the
fertilization of many eggs is assured.
Question 6
Pedicellariae
TX Obj 2; Endoskeleton
8C, 10A,
10B
Madreporite
Ray
Radial
canal
Radial
nerve
Tube feet
Eyespots
Anus
Ring
canal
Ampullae
Nerve ring
Stomach
Mouth
Reproductive
organ
Endoskeletal
plates
Digestive
gland
The sea star displays radial symmetry
because each ray is a duplicate of the others
and all organs extend around a central point
in a radial or circular arrangement.
Question 7
Why is the fossil record of invertebrate
chordates incomplete? (TX Obj 2; 8C, 10A, 10B)
Answer
Sea squirts and lancelets have no bones,
shell, or other hard parts that could form
fossils.
Question 8
Where is a tunicate’s postanal tail?
(TX Obj 2; 8C, 10A, 10B)
Answer
A tunicate possesses a postanal tail only
in its larval stage.
Question 9
Lancelets and tunicates are both _______.
(TX Obj 2; 8C, 10A, 10B, TX Obj 3; 12B, 12E)
A. predators
B. filter feeders
C. parasites
D. decomposers
The answer is B, filter feeders.
Question 10
The tunic of Urochordates is composed of
_______. (TX Obj 2; 8C, 10A, 10B)
A. mesoderm
B. chitin
C. calcium carbonate
D. cellulose
The answer is D, cellulose.
Photo Credits
• General Biological Inc.
• Ward's Natural Science Establishment, Inc.
• Digital Stock
• Ed Shay
• American Petrolium Inst.
• Harris Biological Supply LTD
• Susan Marquart
• Carolina Biological Supply Co.
• PhotoDisc
• Alton Biggs
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