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Chapter 33
Invertebrates
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
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Overview: Life Without a Backbone
• Invertebrates are
animals that lack a
backbone
• They account for 95%
of known animal species
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Eumetazoa
Ancestral colonial
choanoflagellate
Chordata
Echinodermata
Other bilaterians (including
Nematoda, Arthropoda,
Mollusca, and Annelida)
Cnidaria
Porifera
LE 33-2
Deuterostomia
Bilateria
LE 33-3a
A sponge
A jelly
0.5 mm
250 µm
A placozoan (LM)
A kinorhynch (LM)
A marine flatworm
A rotifer (LM)
Ectoprocts
Phoronids
LE 33-3b
A brachiopod
A ribbon worm
5 mm
An acanthocephalan
An octopus
A ctenophore, or comb jelly
A marine annelid
50 µm
A loriciferan (LM)
A priapulan
LE 33-3c
A roundworm
A scorpion
(an arachid)
100 µm
100 µm
A cycliophoran (colorized SEM)
Tardigrades (colorized SEM)
An onychophoran
An acorn worm
A sea urchin
A tunicate
Concept 33.1: Sponges are sessile and have a
porous body and choanocytes
• Sponges, phylum
Porifera, live in both
fresh and marine waters
• Sponges lack true
tissues and organs
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• Sponges are suspension
feeders, capturing food
particles suspended in
the water that passes
through their body
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LE 33-4
Food particles
in mucus
Choanocyte
Flagellum
Choanocytes
Collar
Osculum
Azure vase sponge
(Callyspongia plicifera)
Spongocoel
Phagocytosis of
food particles Amoebocyte
Porocytes
Spicules
Epidermis
Water
flow
Amoebocyte
Mesohyl
• Choanocytes, flagellated collar
cells, generate a water current
through the sponge and ingest
suspended food
• Most sponges are
hermaphrodites: Each individual
functions as both male and
female
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Concept 33.2: Cnidarians have radial symmetry, a
gastrovascular cavity, and cnidocytes
• All animals except sponges
belong to the clade
Eumetazoa, animals with true
tissues
• Phylum Cnidaria is one of the
oldest groups in this clade
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• Cnidarians have diversified into a
wide range of both sessile and
floating forms including jellies,
corals, and hydras
• They exhibit a relatively simple
diploblastic, radial body plan
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• The basic body plan of a cnidarian is a sac
with a central digestive compartment, the
gastrovascular cavity
• A single opening functions as mouth and
anus
• There are two variations on the body
plan: the sessile polyp and floating
medusa
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LE 33-5
Mouth/anus
Polyp
Tentacle
Medusa
Gastrovascular
cavity
Gastrodermis
Body
stalk
Mesoglea
Epidermis
Tentacle
Mouth/anus
• Cnidarians are carnivores that
use tentacles to capture prey
• The tentacles are armed with
cnidocytes, unique cells that
function in defense and
capture of prey
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LE 33-6
Prey
Tentacle
“Trigger”
Nematocyst
Coiled thread
Discharge
of thread
Cnidocyte
• Phylum Cnidaria is divided into
four major classes:
– Hydrozoa
– Scyphozoa
– Cubozoa
– Anthozoa
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LE 33-7
Scyphozoans (jellies)
Hydrozoans
Cubozoan (sea wasp)
Anthozoan
(sea anemone)
Hydrozoans
•Most hydrozoans
alternate between
polyp and medusa
forms
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LE 33-8–3
Reproductive
polyp
Feeding
polyp
Medusa
bud
MEIOSIS
Gonad
Medusa
Egg
SEXUAL
REPRODUCTION
Sperm
ASEXUAL
REPRODUCTION
(BUDDING)
Portion of
a colony
of polyps
FERTILIZATION
Zygote
Developing
polyp
Mature
polyp
Planula
(larva)
1 mm
Key
Haploid (n)
Diploid (2n)
Scyphozoans
•In the class
Scyphozoa, jellies
(medusae) are the
prevalent form of the
life cycle
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Cubozoans
• In the class Cubozoa,
which includes box
jellies and sea wasps,
the medusa is boxshaped and has complex
eyes
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Anthozoans
•Class Anthozoa
includes the corals
and sea anemones,
which occur only as
polyps
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Concept 33.3: Most animals have bilateral
symmetry
• The vast majority of animal
species belong to the clade
Bilateria, which consists of
animals with bilateral
symmetry and triploblastic
development
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Flatworms
• Members of phylum Platyhelminthes
live in marine, freshwater, and damp
terrestrial habitats
• They are flattened dorsoventrally
and have a gastrovascular cavity
• Although flatworms undergo
triploblastic development, they are
acoelomates
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• Flatworms are divided into four classes:
– Turbellaria (mostly free-living
flatworms)
– Monogenea (monogeneans)
– Trematoda (trematodes, or flukes)
– Cestoda (tapworms)
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Turbellarians
• Turbellarians are nearly all
free-living and mostly
marine
• The best-known
turbellarians are commonly
called planarians
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• Planarians have light-sensitive
eyespots and centralized
nerve nets
• The planarian nervous system
is more complex and
centralized than the nerve
nets of cnidarians
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LE 33-10
Pharynx
Gastrovascular
cavity
Eyespots
Ganglia
Ventral nerve cords
Monogeneans and Trematodes
• Monogeneans and trematodes live as
parasites in or on other animals
• They parasitize a wide range of
hosts
• Trematodes that parasitize humans
spend part of their lives in snail
hosts
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LE 33-11
Mature flukes live in the blood vessels
of the human intestine
Male
Female
1 mm
Larvae
penetrate skin
and blood
vessels of
humans.
Blood flukes
reproduce sexually in
the human host.
Fertilized eggs exit
host in feces.
Eggs develop in
water into ciliated
larvae. Larvae
infect snails.
Asexual
reproduction within
snail results in
another type of
motile larva.
Snail host
•Most
monogeneans are
parasites of fish
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Tapeworms
•Tapeworms are
also parasitic
and lack a
digestive system
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LE 33-12
Proglottids with
reproductive structures
200 µm
Scolex
Hooks
Sucker
Rotifers
• Rotifers, phylum Rotifera, are
tiny animals that inhabit fresh
water, the ocean, and damp soil
• Rotifers are smaller than many
protists but are truly
multicellular and have specialized
organ systems
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LE 33-13
0.1 mm
• Rotifers have an alimentary canal: a
digestive tube with a separate mouth
and anus that lies within a fluid-filled
pseudocoelom
• Rotifers reproduce by
parthenogenesis, in which females
produce offspring from unfertilized
eggs
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Lophophorates: Ectoprocts, Phoronids, and
Brachiopods
• Lophophorates have a
lophophore, a
horseshoe-shaped,
suspension-feeding
organ with ciliated
tentacles
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•Ectoprocts are
colonial animals that
superficially
resemble plants
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LE 33-14
Lophophore
Lophophore
Ectoprocts
Phoronids
Brachiopods
•Phoronids are tubedwelling marine
worms ranging from
1 mm to 50 cm in
length
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• Brachiopods superficially
resemble clams and other
hinge-shelled molluscs, but
the two halves of the shell
are dorsal and ventral
rather than lateral, as in
clams
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Nemerteans
•Members of phylum
Nemertea are
commonly called
proboscis worms or
ribbon worms
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• The nemerteans’ unique proboscis is
used for defense and prey capture
and is extended by a fluid-filled sac
• Nemerteans also have a closed
circulatory system, in which the
blood is contained in vessels distinct
from fluid in the body cavity
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Concept 33.4: Molluscs have a muscular foot, a
visceral mass, and a mantle
• Phylum Mollusca includes snails and
slugs, oysters and clams, and
octopuses and squids
• Most molluscs are marine, though
some inhabit fresh water and some
are terrestrial
• Molluscs are soft-bodied animals, but
most are protected by a hard shell
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• All molluscs have a similar body
plan with three main parts:
– Muscular foot
– Visceral mass
– Mantle
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LE 33-16
Visceral mass
Coelom
Heart
Intestine
Nephridium
Gonads
Mantle
Stomach
Mantle
Shell
cavity
Radula
Anus
Gill
Foot
Nerve
cords
Esophagus
Mouth
Radula
Mouth
• Most molluscs have separate
sexes with gonads located in
the visceral mass
• The life cycle of many
molluscs includes a ciliated
larval stage called a
trochophore
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• There are four major classes of molluscs:
– Polyplacophora (chitons)
– Gastropoda (snails and slugs)
– Bivalvia (clams, oysters, and other
bivalves)
– Cephalopoda (squids, octopuses,
cuttlefish, and chambered
nautiluses)
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Chitons
• Class Polyplacophora
consists of the chitons,
oval-shaped marine
animals encased in an
armor of eight dorsal
plates
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Gastropods
•About threequarters of all living
species of molluscs
belong to class
Gastropoda
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LE 33-18
A land snail
A sea slug. Nudibranchs, or sea slugs,
lost their shell during their evolution.
• Most gastropods are marine, but many
are freshwater and terrestrial species
• Most have a single, spiraled shell
• Slugs lack a shell or have a reduced shell
• The most distinctive characteristic of
gastropods is torsion, which causes the
animal’s anus and mantle to end up above
its head
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LE 33-19
Mantle
cavity
Anus
Mouth
Stomach
Intestine
Bivalves
• Molluscs of class Bivalvia
include many species of
clams, oysters, mussels, and
scallops
• They have a shell divided
into two halves
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•The mantle cavity
of a bivalve contains
gills that are used
for feeding as well
as gas exchange
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LE 33-21
Coelom
Hinge area
Mantle
Gut
Heart
Adductor
muscle
Shell
Anus
Mouth
Excurrent
siphon
Palp
Water
flow
Foot
Mantle
cavity
Gill
Incurrent
siphon
Cephalopods
• Class Cephalopoda
includes squids and
octopuses, carnivores
with beak-like jaws
surrounded by tentacles
of their modified foot
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•Most octopuses
creep along the
sea floor in search
of prey
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LE 33-22a
Octopuses are considered among the
most intelligent invertebrates.
•Squids use their
siphon to fire a jet of
water, which allows
them to swim very
quickly
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LE 33-22b
Squids are speedy carnivores
with beaklike jaws and welldeveloped eyes.
•One small group of
shelled cephalopods,
the nautiluses,
survives today
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LE 33-22c
Chambered nautiluses are the only living
cephalopods with an external shell.
Concept 33.5: Annelids are segmented worms
• Annelids have bodies composed of a
series of fused rings
• The phylum Annelida is divided into three
classes:
– Oligochaeta (earthworms and their
relatives)
– Polychaeta (polychaetes)
– Hirudinea (leeches)
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Oligochaetes
• Oligochaetes (class Oligochaeta) are
named for relatively sparse chaetae,
bristles made of chitin
• They include the earthworms and a
variety of aquatic species
• Earthworms eat through soil, extracting
nutrients as the soil moves through the
alimentary canal
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LE 33-23
Cuticle
Epidermis
Circular muscle
Longitudinal muscle
Coelom
Septum (partition
between segments)
Metanephridium
Anus
Dorsal vessel
Chaetae
Intestine
Nerve Ventral vessel
cords
Nephrostome
Clitellum
Esophagus
Crop
Pharynx
Giant Australian earthworm
Cerebral ganglia
Intestine
Gizzard
Mouth
Subpharyngeal
ganglion
Metanephridium
Circulatory
system
Ventral nerve cords
with segmental
ganglia
Polychaetes
•Members of class
Polychaetes have
paddlelike parapodia
that work as gills and
aid in locomotion
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LE 33-24
Parapodia
Leeches
•Members of class
Hirudinea are bloodsucking parasites,
such as leeches
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Concept 33.6: Nematodes are nonsegmented
pseudocoelomates covered by a tough cuticle
• Nematodes, or roundworms, are
found in most aquatic habitats, in the
soil, in moist tissues of plants, and in
body fluids and tissues of animals
• The cylindrical bodies of nematodes
(phylum Nematoda) are covered by a
tough coat called a cuticle
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LE 33-26
25 µm
•Some species of
nematodes are
important parasites
of plants and
animals
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LE 33-27
Encysted juveniles
Muscle tissue
50 µm
Concept 33.7: Arthropods are segmented coelomates
that have an exoskeleton and jointed appendages
• Two out of every three known
species of animals are
arthropods
• Members of the phylum
Arthropoda are found in
nearly all habitats of the
biosphere
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General Characteristics of Arthropods
• The diversity and success
of arthropods are largely
related to their
segmentation, hard
exoskeleton, and jointed
appendages
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•Early arthropods,
such as trilobites,
showed little variation
from segment to
segment
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• As arthropods evolved, the
segments fused, and the
appendages became more
specialized
• The appendages of some living
arthropods are modified for
many different functions
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LE 33-29
Cephalothorax
Abdomen
Thorax
Antennae
(sensory
reception)
Head
Swimming
appendages
(two sets
located under
abdomen
Walking legs
Pincer (defense)
Mouthparts (feeding)
• The body of an arthropod is
completely covered by the
cuticle, an exoskeleton made of
chitin
• When an arthropod grow, it molts
its exoskeleton in a process
called ecdysis
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• Arthropods have an open circulatory
system in which fluid called
hemolymph is circulated into the
spaces surrounding the tissues and
organs
• A variety of organs specialized for
gas exchange have evolved in
arthropods
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• Molecular evidence suggests that living
arthropods consist of four major lineages that
diverged early in the phylum’s evolution:
– Cheliceriforms (sea spiders, horseshoe
crabs, scorpions, ticks, mites, and spiders)
– Myriapods (centipedes and millipedes)
– Hexapods (insects and relatives)
– Crustaceans (crabs, lobsters, shrimps,
barnacles, and many others)
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Cheliceriforms
• Cheliceriforms, subphylum
Cheliceriformes, are named for
clawlike feeding appendages
called chelicerae
• Most marine cheliceriforms are
extinct, but some species survive
today, including horseshoe crabs
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• Most modern
cheliceriforms are
arachnids, which include
spiders, scorpions, ticks,
and mites
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LE 33-31a
Scorpions have pedipalps that are pincers
specialized for defense and the capture of
food. The tip of the tail bears a poisonous
stinger.
LE 33-31b
50 µm
Dust mites are ubiquitous scavengers in
human dwellings but are harmless except to
those people who are allergic to them
(colorized SEM).
LE 33-31c
Web-building spiders are generally
most active during the daytime.
• Arachnids have an abdomen
and a cephalothorax, which
has six pairs of appendages,
the most anterior of which
are the chelicerae
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LE 33-32
Stomach
Intestine
Brain
Heart
Digestive
gland
Eyes
Ovary
Poison
gland
Anus
Book lung
Gonopore
(exit for eggs) Sperm
Silk gland
receptacle
Spinnerets
Chelicera
Pedipalp
Myriapods
• Subphylum Myriapoda includes
millipedes and centipedes
• Millipedes, class Diplopoda, have
many legs
• Each trunk segment has two pairs
of legs
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• Centipedes, class Chilopoda,
are carnivores with jaw-like
mandibles
• They have one pair of legs
per trunk segment
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Insects
• Subphylum Hexapoda, insects and
relatives, has more species than all
other forms of life combined
• They live in almost every terrestrial
habitat and in fresh water
• The internal anatomy of an insect
includes several complex organ
systems
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LE 33-35
Abdomen
Thorax Head
Compound eye
Antennae
Dorsal
artery
Crop
Cerebral ganglion
Heart
Anus
Vagina
Malpighian tubules
Ovary
Tracheal tubes
Nerve cords
Mouthparts
• Flight is one key to the great
success of insects
• An animal that can fly can
escape predators, find food,
and disperse to new habitats
much faster than organisms
that can only crawl
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• Many insects undergo
metamorphosis during their
development
• In incomplete metamorphosis,
the young, called nymphs,
resemble adults but are smaller
and go through a series of molts
until they reach full size
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• Insects with complete
metamorphosis have larval stages
known by such names as maggot,
grub, or caterpillar
• The larval stage looks entirely
different from the adult stage
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LE 33-36
Larva (caterpillar)
Pupa
Pupa
Emerging adult
Adult
•Insects are
classified into
about 26 orders
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LE 33-37aA
ORDER
Blattodea
APPROXIMATE
NUMBER OF
SPECIES
4,000
MAIN CHARACTERISTICS
Cockroaches have a dorsoventrally flattened body,
with legs modified for rapid running. Forewings,
when present, are leathery, whereas hind wings are
fanlike. Fewer than 40 cockroach species live in
houses; the rest exploit habitats ranging from
tropical forest floors to caves and deserts.
EXAMPLES
German
cockroach
LE 33-37bA
ORDER
Coleoptera
APPROXIMATE
NUMBER OF
SPECIES
350,000
MAIN CHARACTERISTICS
Beetles comprise the most species-rich order of
insects. They have two pairs of wings, one of which
is thick and leathery, the other membranous. They
have an armored exoskeleton and mouthparts
adapted for biting and chewing. Beetles undergo
complete metamorphosis.
EXAMPLES
Japanese
beetle
LE 33-37cA
ORDER
Dermaptera
APPROXIMATE
NUMBER OF
SPECIES
1,200
MAIN CHARACTERISTICS
Earwigs are generally nocturnal scavengers. While
some species are wingless, others have two pairs of
wings, one of which is thick and leathery, the other
membranous. Earwigs have biting mouthparts and
large posterior pincers. They undergo incomplete
metamorphosis.
EXAMPLES
Earwig
LE 33-37dA
ORDER
Diptera
APPROXIMATE
NUMBER OF
SPECIES
151,000
MAIN CHARACTERISTICS
Dipterans have one pair of wings; the second pair has
become modified into balancing organs called halteres.
Their head is large and mobile; their mouthparts are
adapted for sucking, piercing, or lapping. Dipterans
undergo complete metamorphosis. Flies and mosquitoes
are among the best-known dipterans, which live as
scavengers, predetors, and parasites.
EXAMPLES
Horsefly
LE 33-37eA
ORDER
Hemiptera
APPROXIMATE
NUMBER OF
SPECIES
85,000
MAIN CHARACTERISTICS
Hemipterans are so-called “true bugs,” including
bed bugs, assassin bugs, and chinch bugs. (Insects
in other orders are sometimes erroneously called
bugs.) Hemipterans have two pairs of wings, one
pair partly leathery, the other membranous. They
have piercing or sucking mouthparts and undergo
incomplete metamorphosis.
EXAMPLES
Leaffooted
bug
LE 33-37fA
ORDER
Hymenoptera
APPROXIMATE
NUMBER OF
SPECIES
125,000
MAIN CHARACTERISTICS
Ants, bees, and wasps are generally highly social
insects. They have two pairs of membranous wings,
a mobile head, and chewing or sucking mouthparts.
The females of many species have a posterior
stinging organ. Hymenopterans undergo complete
metamorphosis.
EXAMPLES
Cicada-killer wasp
LE 33-37gA
ORDER
Isoptera
APPROXIMATE
NUMBER OF
SPECIES
2,000
MAIN CHARACTERISTICS
Termites are widespread social insects that produce
enormous colonies. It had been estimated that there
are 700 kg of termites for every person on Earth!
Some termites have two pairs of membranous
wings, while others are wingless. They feed on wood
with the aid of microbial symbionts carried in
specialized chambers in their hindgut.
EXAMPLES
Termite
LE 33-37aB
ORDER
Lepidoptera
APPROXIMATE
NUMBER OF
SPECIES
120,000
MAIN CHARACTERISTICS
Butterflies and moths are among the best-known
insects. They have two pairs of wings covered with
tiny scales. To feed, they uncoil a long proboscis.
Most feed on nectar, but some species feed on other
substances, including animal blood or tears.
EXAMPLES
Swallowtail
butterfly
LE 33-37bB
ORDER
Odonata
APPROXIMATE
NUMBER OF
SPECIES
5,000
MAIN CHARACTERISTICS
Dragonflies and damselflies have two pairs of large,
membranous wings. They have an elongated
abdomen, large, compound eyes, and chewing
mouthparts. They undergo incomplete
metamorphosis and are active predators.
EXAMPLES
Dragonfly
LE 33-37cB
ORDER
Orthoptera
APPROXIMATE
NUMBER OF
SPECIES
13,000
MAIN CHARACTERISTICS
Grasshoppers, crickets, and their relatives are mostly
herbivorous. They have large hind legs adapted for
jumping, two pairs of wings (one leathery, one
membranous), and biting or chewing mouthparts.
Males commonly make courtship sounds by rubbing
together body parts, such as a ridge of their hind leg.
Orthopterans undergo incomplete metamorphosis.
EXAMPLES
Katydid
LE 33-37dB
ORDER
Phasmida
APPROXIMATE
NUMBER OF
SPECIES
2,600
MAIN CHARACTERISTICS
Stick insects and leaf insects are exquisite mimics of
plants. The eggs of some species even mimic seeds of
the plants on which the insects live. Their body is
cylindrical or flattened dorsoventrally. They lack
forewings but have fanlike hind wings. Their
mouthparts are adapted for biting or chewing.
EXAMPLES
Stick insect
LE 33-37eB
ORDER
Phthiraptera
APPROXIMATE
NUMBER OF
SPECIES
2,400
MAIN CHARACTERISTICS
Commonly called sucking lice, these insects spend
their entire life as an ectoparasite feeding on the hair
or feathers of a single host. Their legs, equipped with
clawlike tarsi, are adapted for clinging to their hosts.
They lack wings and have reduced eyes. Sucking lice
undergo incomplete metamorphosis.
EXAMPLES
Human
body
louse
LE 33-37fB
ORDER
Siphonaptera
APPROXIMATE
NUMBER OF
SPECIES
2,400
MAIN CHARACTERISTICS
Fleas are bloodsucking ectoparasites on birds and
mammals. Their body is wingless and laterally
compressed. Their legs are modified for clinging to
their hosts and for long-distance jumping. They
undergo complete metamorphosis.
EXAMPLES
Flea
LE 33-37gB
ORDER
Thysanura
APPROXIMATE
NUMBER OF
SPECIES
450
MAIN CHARACTERISTICS
Silverfish are small, wingless insects with a flattened
body and reduced eyes. They live in leaf litter or
under bark. They can also infest buildings, where
they can become pests.
EXAMPLES
Silverfish
LE 33-37hB
ORDER
Trichoptera
APPROXIMATE
NUMBER OF
SPECIES
7,100
MAIN CHARACTERISTICS
The larvae of caddisflies live in streams, where they
make houses from sand grains, wood fragments, or
other material held together by silk, Adults have two
pairs of hairy wings and chewing or lapping
mouthparts. They undergo complete metamorphosis.
EXAMPLES
Caddisfly
Crustaceans
• While arachnids and insects thrive
on land, crustaceans, for the most
part, have remained in marine and
freshwater environments
• Crustaceans, subphylum Crustacea,
typically have branched appendages
that are extensively specialized for
feeding and locomotion
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• Decapods are all
relatively large
crustaceans and include
lobsters, crabs,
crayfish, and shrimp
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Planktonic crustaceans
include many species of
copepods, which are among
the most numerous of all
animals
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Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Barnacles are a group of
mostly sessile
crustaceans
• They have a cuticle that
is hardened into a shell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Concept 33.8: Echinoderms and chordates are
deuterostomes
• Sea stars and other
echinoderms, phylum
Echinodermata, may seem to
have little in common with
phylum Chordata, which
includes the vertebrates
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Chordates and echinoderms share
characteristics of deuterostomes:
– Radial cleavage
– Development of the coelom from
the archenteron
– Formation of the mouth at the
end of the embryo opposite the
blastopore
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Echinoderms
• Sea stars and most other echinoderms
are slow-moving or sessile marine animals
• A thin, bumpy or spiny skin covers an
endoskeleton of hard calcareous plates
• Unique to echinoderms is a water vascular
system, a network of hydraulic canals
branching into tube feet that function in
locomotion, feeding, and gas exchange
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LE 33-39
Spine
Anus Stomach
Gills
Central disk
Madreporite
Digestive glands
Radial
nerve
Ring
canal
Gonads
Ampulla
Radial canal
Podium
Tube
feet
• Radial anatomy of many echinoderms evolved
from the bilateral symmetry of ancestors
• Living echinoderms are divided into six classes:
– Asteroidia (sea stars)
– Ophiuroidea (brittle stars)
– Echinoidea (sea urchins and sand dollars)
– Crinoidea (sea lilies and feather stars)
– Holothuroidea (sea cucumbers)
– Concentricycloidea (sea daisies)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Sea Stars
• Sea stars, class Asteroidea, have
multiple arms radiating from a
central disk
• The undersurfaces of the arms
bear tube feet, each of which
can act like a suction disk
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 33-40a
A sea star (class Asteroidea)
Brittle Stars
•Brittle stars have a
distinct central disk
and long, flexible
arms
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LE 33-40b
A brittle star (class Ophiuroidea)
Sea Urchins and Sand Dollars
•Sea urchins and
sand dollars have no
arms but have five
rows of tube feet
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LE 33-40c
A sea urchin (class Echinoidea)
Sea Lilies and Feather Stars
• Sea lilies live attached
to the substrate by a
stalk
• Feather stars crawl
using long, flexible arms
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LE 33-40d
A feather star (class Crinoidea)
Sea Cucumbers
• Sea cucumbers do not look
much like other echinoderms
• They lack spines, and their
endoskeleton is much reduced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 33-40e
A sea cucumber (class Holothuroidea)
Sea Daisies
•Sea daisies were
discovered in 1986,
and only two species
are known
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
LE 33-40f
A sea daisy (class Concentricycloidea)
Chordates
• Phylum Chordata consists of two
subphyla of invertebrates as well
as hagfishes and vertebrates
• Chordates share many features
of embryonic development with
echinoderms
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings