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Section Objectives: 29.1
• Compare similarities and differences among
the classes of echinoderms.
• Interpret the evidence biologists have for
determining that echinoderms are close
relatives of chordates.
• _________ move by means of hundreds of
hydraulic, suction-cup-tipped appendages
and have skin covered with tiny, jawlike
• Echinoderms are
found in all the
_____ of the world.
• If you were to examine the skin of several
different echinoderms, you would find that
they all have a hard, _____, or bumpy
endoskeleton covered by a thin ________.
• ___ ___, sometimes called starfishes, may
not appear spiny at first glance, but a close
look reveals that their long, tapering arms,
called ___, are covered with short, rounded
• Some of the spines found on sea stars and
___ _____ have become modified into
pincer-like appendages called _________
(PEH dih sih LAHR ee ay).
• An echinoderm
uses its jaw-like
_______ for
protection and
for cleaning the
surface of its
• You may remember that ____________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
• The water vascular system is a _____ system
that operates under water pressure.
• Water enters and leaves the water vascular
system of a sea star through the _______
(mah druh POHR ite), a sieve-like, diskshaped opening on the upper surface of the
echinoderm’s body.
• The underside of a sea star has ____ feet that
run along a groove on the underside of each
• Tube feet are hollow, thin-walled tubes that
end in a ______ cup.
• Tube feet look somewhat like miniature
• The round, muscular structure called the
______ (AM pew lah) works something like
the bulb of a dropper.
• Each ____ foot
independently of
the others, and the
animal moves along
slowly by
alternately pushing
out and pulling in
its tube feet.
• Tube feet also function in gas exchange and
excretion. Gases are exchanged and wastes
are eliminated by ________ through the thin
walls of the tube feet.
• All echinoderms have a mouth, stomach,
and intestines, but their methods of
obtaining food vary.
• Sea stars are _________ and prey on
worms or on mollusks such as clams.
• Most sea urchins are ___________ and
graze on algae.
• ______ stars, ___ lilies, and sea _______
feed on dead and decaying matter that drifts
down to the ocean floor.
• Echinoderms
have no head or
brain, but they
do have a ____
____ ____ that
surrounds the
• Nerves extend from the _____ ____down
each ray.
• Each ______ nerve then branches into a
nerve net that provides sensory information
to the animal.
• ___ ____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 ______ and
consisting of a cluster of light-detecting cells
is located at the tip of each arm, on the
• _______ enable sea stars to detect the
intensity of light.
• Sea stars also have chemical ______ on their
tube feet.
• If you examine the larval stages of
echinoderms, you will find that they have
___________ ______.
• Through __________, the free-swimming
larvae make dramatic changes in both body
parts and in symmetry.
• Echinoderms are deuterostomes.
• This pattern of development indicates a
close relationship to ______, which are also
• Approximately 6000 species of echinoderms
exist today.
• About one-fourth
of these species
are in the class
_______ (AS tuh
ROY dee uh), to
which the sea
stars belong.
• 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.
• 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
• Most species of sea stars have ____ rays, but
some have more. Some species may have
more than 40 rays.
• Brittle stars are extremely ______.
• 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 ________.
• Brittle stars propel themselves with the
snake like, slithering motion of their flexible
• They use their tube
feet to pass
particles of food
along the rays and
into the mouth in
the ____ ____.
• Sea urchins and sand dollars are _____ 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
• A sand dollar has tube feet that protrude
from the petal-like markings on its upper
• These tube feet are modified into ____ and
are used for respiration.
• Tube feet on the
animal’s bottom
surface aid in
bringing food
particles to the
• 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 ________.
• Sea cucumbers are so called because of their
vegetable-like appearance.
• Their leathery covering allows them
flexibility as they move along the ocean
• 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
_______ in a few weeks.
• Sea cucumbers reproduce by shedding ____
and _____ into the water, where fertilization
• Sea lilies and feather stars resemble plants in
some ways.
• Sea lilies are the only ______ echinoderms.
• Feather stars are sessile only in _____form.
The adult feather star uses its feathery arms
to swim from place to place.
• 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.
• The earliest echinoderms may have been
bilaterally symmetrical as adults, and
probably were attached to the ocean floor by
• Another view of the earliest echinoderms is
that they were bilateral and ____ swimming.
• The echinoderms represent the only major
group of deuterostome ___________.
• This pattern of development is one piece of
evidence biologists have for placing
echinoderms as the closest invertebrate
relatives of the ________.
• 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
Section Objectives: 29.2
• Summarize the characteristics of chordates.
• Explain how invertebrate chordates are
related to vertebrates.
• Distinguish between sea squirts and
• The phylum _________includes three
subphyla: Urochordata, the ________ (sea
squirts); Cephalochordata, the ______; and
Vertebrata, the vertebrates.
• Invertebrate chordates have a ______, a
dorsal hollow nerve cord, ______pouches,
and a ______ tail at some time during their
• In addition, all chordates have ______
symmetry, a well-developed ______, and
Dorsal hollow
nerve cord
Muscle blocks Postanal
• The embryos of all
chordates have a
_____ (NOH tuh
kord) — a long,
semirigid, rod-like
structure located
between the
digestive system
and the dorsal
hollow nerve cord.
Nerve cord
Gill slits
• In invertebrate chordates, the notochord may
be retained into adulthood. But in vertebrate
chordates, this structure is replaced by a
• ________ chordates do not develop a
• The pharyngeal pouches of a chordate
embryo are paired openings located in the
_______, behind the mouth.
• In aquatic chordates, pharyngeal pouches
develop openings called _____ ____.
• In terrestrial chordates, pharyngeal pouches
develop into other structures.
• At some point in
development, all
chordates have a _____
chordates, and
during the early
development of the
human _____, there
is a postanal tail that
Postanal tail
disappears as
• In most animals that have
tails, the digestive system
extends to the tip of the
tail, where the ____ is
• _______, however,
usually have a tail that
extends beyond the
• Muscle _____ aid in movement of the tail.
• Muscle blocks are modified body segments
that consist of _______ muscle layers.
• Muscle blocks are anchored by the
notochord, which gives the muscles a firm
structure to pull against.
• _______ 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
• 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.
• Although adult tunicates do not appear to
have any shared chordate features, the _____
stage, has a tail that makes it look similar to
a tadpole.
• Tunicate larvae do not ___and are free
swimming after hatching.
• They soon settle and attach themselves with
a sucker to boats, rocks, and the ocean
• Many adult tunicates secrete a ____, a tough
sac made of _______, around their bodies.
• Colonies of tunicates sometimes secrete just
one big tunic that has a common opening to
the outside.
• Only the ______ ____in adult tunicates
indicate their chordate relationship.
• If you remove a tunicate from its sea home,
it might squirt out a jet of water-hence the
name sea squirt.
• ______ are small, streamlined, and common
marine animals, usually about 5 cm long.
• Like tunicates, lancelets are ____ ____.
• Unlike tunicates, however, lancelets retain
all their chordate features throughout life.
Oral hood with tentacles
Dorsal hollow
nerve cord
Postanal tail
Muscle blocks
Gill slits in
• Although lancelets look somewhat similar to
fishes, they have only one layer of skin, with
no pigment and no scales.
• Lancelets do not have a distinct ____, but
they do have light sensitive cells on the
_______ end.
• They also have a ____ that covers the mouth
and the sensory _______ surrounding it.
• 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 ______animals that fed
by capturing food in tentacles.
• 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.