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Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
PowerPoint®
Lecture Presentations for
Biology
Eighth Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero, updated by Erin Barley with contributions from Joan Sharp
Chapter 33
Invertebrates

Overview: Life Without a Backbone
• Invertebrates are animals that lack a
backbone
• They account for 95% of known animal species

Fig. 33-2
ANCESTRAL
PROTIST
Common
ancestor of
all animals
Calcarea
and Silicea
Eumetazoa
Bilateria
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia

Fig. 33-3-1
Calcarea and Silicea (5,500 species)
A sponge
Cnidaria (10,000 species)
A jelly
Acoela (400 species)
Acoel flatworms (LM)
1.5 mm
LOPHOTROCHOZOANS
Platyhelminthes (20,000 species)
A marine flatworm
Ectoprocta (4,500 species)
Ectoprocts A brachiopod
Brachiopoda (335 species)
Rotifera (1,800 species)
A rotifer (LM)
A ctenophore, or comb jelly
Ctenophora (100 species)
A placozoan (LM)
0.5 mm
Placozoa (1 species)

Fig. 33-3-2
An acanthocephalan (LM)
Acanthocephala (1,100 species)
Nemertea (900 species)
A ribbon worm
ECDYSOZOA
Loricifera (10 species) Priapula (16 species)
A loriciferan (LM) A priapulan
50 µm
Cycliophora (1 species)
Mollusca (93,000 species)
A cycliophoran (colorized SEM)
100 µm
An octopus
Annelida (16,500 species)
A marine annelid

Fig. 33-3-3
Tardigrada (800 species)
Nematoda (25,000 species)
Onychophora (110 species)
Arthropoda (1,000,000 species)
DEUTEROSTOMIA
Hemichordata (85 species)
Echinodermata (7,000 species) Chordata (52,000 species)
Tardigrades (colorized SEM)
100 µm
A roundworm
An acorn worm
A sea urchin
An onychophoran
A scorpion
(an arachnid)
A tunicate

Fig. 33-3c
A placozoan (LM)
0.5 mm

Fig. 33-3d
A ctenophore, or comb jelly

Fig. 33-3e
Acoel flatworms (LM)
1.5 mm

Fig. 33-3j
An acanthocephalan (LM)

Fig. 33-3k
A cycliophoran (colorized SEM)
100 µm

Fig. 33-3o
A loriciferan (LM)
50 µm

Fig. 33-3q
Tardigrades (colorized SEM)
100 µm

Fig. 33-3t
A scorpion
(an arachnid)

Concept 33.1: Sponges are basal animals that lack
true tissues
• Sponges are sedentary animals from the phyla
Calcarea and Silicea
• They live in both fresh and marine waters
• Sponges lack true tissues and organs

Fig. 33-UN1
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia

• Sponges are suspension feeders, capturing
food particles suspended in the water that pass
through their body
• Choanocytes, flagellated collar cells, generate
a water current through the sponge and ingest
suspended food
• Water is drawn through pores into a cavity
called the spongocoel, and out through an
opening called the osculum

Fig. 33-4
Azure vase sponge (Callyspongia
plicifera)
Spongocoel
Osculum
Pore
Epidermis Water
flow
Mesohyl
Choanocyte
Flagellum
Collar
Food particles
in mucus
Choanocyte
Amoebocyte
Phagocytosis of
food particles
Spicules
Amoebocytes

• Sponges consist of a noncellular mesohyl
layer between two cell layers
• Amoebocytes are found in the mesohyl and
play roles in digestion and structure
• Most sponges are hermaphrodites: Each
individual functions as both male and female

Concept 33.2: Cnidarians are an ancient phylum of
eumetazoans
• All animals except sponges and a few other
groups belong to the clade Eumetazoa,
animals with true tissues
• Phylum Cnidaria is one of the oldest groups in
this clade

Fig. 33-UN2
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia

• Cnidarians have diversified into a wide range of
both sessile and motile forms including jellies,
corals, and hydras
• They exhibit a relatively simple diploblastic,
radial body plan

• 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 motile medusa

Fig. 33-5
Polyp
Mouth/anus
Body
stalk
Tentacle
Gastrovascular
cavity
Gastrodermis
Mesoglea
Epidermis
Tentacle
Mouth/anus
Medusa

• 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
• Nematocysts are specialized organelles within
cnidocytes that eject a stinging thread

Fig. 33-6
Tentacle
Nematocyst
“Trigger”
Cuticle
of prey
Thread
discharges
Thread
(coiled)
Cnidocyte
Thread

• Phylum Cnidaria is divided into four major
classes:
– Hydrozoa
– Scyphozoa
– Cubozoa
– Anthozoa

Fig. 33-7
a) Colonial polyps (class
Hydrozoa)
(b) Jellies (class
Scyphozoa)
Sea wasp (class
Cubozoa)
(d) Sea anemone (class
Anthozoa)
(c)

Fig. 33-7a
(a) Colonial polyps (class
Hydrozoa)

Fig. 33-7b
(b) Jellies (class
Scyphozoa)

Fig. 33-7c
(c) Sea wasp (class
Cubozoa)

Fig. 33-7d
(d) Sea anemone (class
Anthozoa)

Hydrozoans
• Most hydrozoans alternate between polyp and
medusa forms
Video: Hydra BuddingVideo: Hydra Budding
Video: Hydra Releasing SpermVideo: Hydra Releasing Sperm
Video: Hydra Eating Daphnia (time lapse)Video: Hydra Eating Daphnia (time lapse)

Fig. 33-8-1
Feeding
polyp
Reproductive
polyp
Medusa
bud
Medusa
ASEXUAL
REPRODUCTION
(BUDDING)Portion of
a colony
of polyps
1mm
Key
Haploid (n)
Diploid (2n)

Fig. 33-8-2
Feeding
polyp
Reproductive
polyp
Medusa
bud
Medusa
ASEXUAL
REPRODUCTION
(BUDDING)Portion of
a colony
of polyps
1mm
Key
Haploid (n)
Diploid (2n)
Gonad
SEXUAL
REPRODUCTION
MEIOSIS
FERTILIZATION
Egg Sperm
Zygote

Fig. 33-8-3
Feeding
polyp
Reproductive
polyp
Medusa
bud
Medusa
ASEXUAL
REPRODUCTION
(BUDDING)Portion of
a colony
of polyps
1mm
Key
Haploid (n)
Diploid (2n)
Gonad
SEXUAL
REPRODUCTION
MEIOSIS
FERTILIZATION
Egg Sperm
Zygote
Planula
(larva)
Developing
polyp
Mature
polyp

Scyphozoans
• In the class Scyphozoa, jellies (medusae) are
the prevalent form of the life cycle
Video: Jelly SwimmingVideo: Jelly Swimming
Video: Thimble JelliesVideo: Thimble Jellies

Cubozoans
• In the class Cubozoa, which includes box
jellies and sea wasps, the medusa is box-
shaped and has complex eyes
• Cubozoans often have highly toxic cnidocytes

Anthozoans
• Class Anthozoa includes the corals and sea
anemones, which occur only as polyps
Video: Clownfish and AnemoneVideo: Clownfish and Anemone
Video: Coral ReefVideo: Coral Reef

Concept 33.3: Lophotrochozoans, a clade identified
by molecular data, have the widest range of animal
body forms
• Bilaterian animals have bilateral symmetry and
triploblastic development
• The clade Bilateria contains Lophotrochozoa,
Ecdysozoa, and Deuterostomia

Fig. 33-UN3
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia

• The clade Lophotrochozoa was identified by
molecular data
• Some develop a lophophore for feeding, others
pass through a trochophore larval stage, and a
few have neither feature
• Lophotrochozoa includes the flatworms,
rotifers, ectoprocts, brachiopods, molluscs, and
annelids

Flatworms
• Members of phylum Platyhelminthes live in
marine, freshwater, and damp terrestrial
habitats
• Although flatworms undergo triploblastic
development, they are acoelomates
• They are flattened dorsoventrally and have a
gastrovascular cavity
• Gas exchange takes place across the surface,
and protonephridia regulate the osmotic
balance

• Flatworms are divided into four classes:
– Turbellaria (mostly free-living flatworms)
– Monogenea (monogeneans)
– Trematoda (trematodes, or flukes)
– Cestoda (tapeworms)

Turbellarians
• Turbellarians are nearly all free-living and
mostly marine
• The best-known turbellarians are commonly
called planarians

• Planarians have light-sensitive eyespots and
centralized nerve nets
• The planarian nervous system is more complex
and centralized than the nerve nets of
cnidarians
• Planarians are hermaphrodites and can
reproduce sexually, or asexually through
fission

Fig. 33-10
Pharynx
Gastrovascular
cavity
Mouth
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, and
most have complex life cycles with alternating
sexual and asexual stages
• Trematodes that parasitize humans spend part
of their lives in snail hosts
• Most monogeneans are parasites of fish

Fig. 33-11
Human host
Motile larva
Snail host
Ciliated larva
Male
Female
1 mm

Tapeworms
• Tapeworms are parasites of vertebrates and
lack a digestive system
• Tapeworms absorb nutrients from the host’s
intestine
• Fertilized eggs, produced by sexual
reproduction, leave the host’s body in feces

Fig. 33-12
Proglottids with
reproductive structures
Hooks
Sucker
Scolex
200 µm

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
Video: RotiferVideo: Rotifer

Fig. 33-13
Jaws Crown
of cilia
Anus
Stomach 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
• Some species are unusual in that they lack
males entirely

Lophophorates: Ectoprocts and Brachiopods
• Lophophorates have a lophophore, a
horseshoe-shaped, suspension-feeding organ
with ciliated tentacles
• Lophophorates include two phyla: Ectoprocta
and Brachiopoda
• Ectoprocts (also called bryozoans) are
colonial animals that superficially resemble
plants
• A hard exoskeleton encases the colony, and
some species are reef builders

Fig. 33-14
Lophophore
a) Ectoproct (sea mat)
Lophophore
(b) Brachiopods

Fig. 33-14a
(a) Ectoproct (sea mat)
Lophophore

• 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

Fig. 33-14b
(b) Brachiopods
Lophophore

Molluscs
• 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

• All molluscs have a similar body plan with three
main parts:
– Muscular foot
– Visceral mass
– Mantle
• Many molluscs also have a water-filled mantle
cavity, and feed using a rasplike radula

Fig. 33-15
Nephridium Visceral mass
Coelom
Mantle
Mantle
avity
Heart
Intestine
Gonads
Stomach
Shell
Radula
Mouth
EsophagusNerve
cords
Foot
Gill
Anus
Mouth
Radula

• 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

• 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)

Chitons
• Class Polyplacophora consists of the chitons,
oval-shaped marine animals encased in an
armor of eight dorsal plates

Gastropods
• About three-quarters of all living species of
molluscs are gastropods
Video: NudibranchsVideo: Nudibranchs

Fig. 33-17
a) A land snail
(b) A sea slug

• 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

Fig. 33-18
Mouth
Anus
Mantle
cavity
Stomach Intestine

Bivalves
• Molluscs of class Bivalvia include many
species of clams, oysters, mussels, and
scallops
• They have a shell divided into two halves

• The mantle cavity of a bivalve contains gills
that are used for feeding as well as gas
exchange

Fig. 33-20
Mouth
Digestive
gland
Mantle
Hinge area
Gut
Coelom
Heart Adductor
muscle
Anus
Excurrent
siphon
Water
flow
Incurrent
siphonGillGonad
Mantle
cavity
Foot
Palp
Shell

Cephalopods
• Class Cephalopoda includes squids and
octopuses, carnivores with beak-like jaws
surrounded by tentacles of their modified foot
• Most octopuses creep along the sea floor in
search of prey

Fig. 33-21
Octopus
Squid
Chambered
nautilus

• Squids use their siphon to fire a jet of water,
which allows them to swim very quickly

• One small group of shelled cephalopods, the
nautiluses, survives today

Fig. 33-21c
Chambered
nautilus

• Cephalopods have a closed circulatory system,
well-developed sense organs, and a complex
brain
• Shelled cephalopods called ammonites were
common but went extinct at the end of the
Cretaceous

Annelids
• 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)

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
• Earthworms are hermaphrodites but cross-
fertilize Video: Earthworm LocomotionVideo: Earthworm Locomotion

Fig. 33-22
Epidermis
Circular
muscle
Longitudinal
muscle
Dorsal vessel
Chaetae
Intestine
Nephrostome
Fused
nerve
cords
Ventral
vessel
Metanephridium
Septum
(partition
between
segments)
Coelom
Cuticle
Anus
Metanephridium
Crop
Intestine
Gizzard
Ventral nerve cord with
segmental gangliaBlood
vessels
Subpharyngeal
ganglion
Mouth
Cerebral ganglia
Pharynx
Esophagus
Clitellum
Giant Australian earthworm

Polychaetes
• Members of class Polychaetes have paddle-
like parapodia that work as gills and aid in
locomotion
Video: TubewormsVideo: Tubeworms

Leeches
• Members of class Hirudinea are blood-sucking
parasites, such as leeches
• Leeches secrete a chemical called hirudin to
prevent blood from coagulating

Concept 33.4: Ecdysozoans are the most species-
rich animal group
• Ecdysozoans are covered by a tough coat
called a cuticle
• The cuticle is shed or molted through a
process called ecdysis
• The two largest phyla are nematodes and
arthropods

Fig. 33-UN4
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia

Nematodes
• 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
• They have an alimentary canal, but lack a
circulatory system
• Reproduction in nematodes is usually sexual,
by internal fertilization
Video:Video: C.C. eleganselegans CrawlingCrawling
Video:Video: C.C. eleganselegans Embryo Development (Time Lapse)Embryo Development (Time Lapse)

• Some species of nematodes are important
parasites of plants and animals

Fig. 33-26
Encysted juveniles Muscle tissue 50 µm

Arthropods
• 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

Arthropod Origins
• The arthropod body plan consists of a
segmented body, hard exoskeleton, and jointed
appendages, and dates to the Cambrian
explosion (535–525 million years ago)
• Early arthropods show little variation from
segment to segment

• Arthropod evolution is characterized by a
decrease in the number of segments and an
increase in appendage specialization
• These changes may have been caused by
changes in Hox gene sequence or regulation

Fig. 33-28
EXPERIMENT
RESULTS
Origin of Ubx and
abd-A Hox genes?
Other
ecdysozoans
Arthropods
OnychophoransCommon ancestor of
onychophorans and arthropods
Ubx or
abd-A genes
expressed
Ant = antenna
J = jaws
L1–L15 = body segments

Fig. 33-28a
EXPERIMENT
Other
ecdysozoans
Origin of Ubx and
abd-A Hox genes?
Common ancestor of
onychophorans and arthropods
Arthropods
Onychophorans

Fig. 33-28b
RESULTS
Ubx or
abd-A genes
expressed
Ant = antenna
J = jaws
L1–L15 = body segments

General Characteristics of Arthropods
• The appendages of some living arthropods are
modified for many different functions
Video: Lobster Mouth PartsVideo: Lobster Mouth Parts

Fig. 33-29
Cephalothorax
Antennae
(sensory
reception) Head
Thorax
Abdomen
Swimming appendages
(one pair located
under each
abdominal segment)
Walking legs
Mouthparts (feeding)Pincer (defense)

• The body of an arthropod is completely
covered by the cuticle, an exoskeleton made of
layers of protein and the polysaccharide chitin
• When an arthropod grows, it molts its
exoskeleton

• 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

• 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)

Cheliceriforms
• Cheliceriforms, subphylum Cheliceriformes,
are named for clawlike feeding appendages
called chelicerae
• The earliest cheliceriforms were eurypterids
(water scorpions)
• Most marine cheliceriforms (including
eurypterids) are extinct, but some species
survive today, including horseshoe crabs

• Most modern cheliceriforms are arachnids,
which include spiders, scorpions, ticks, and
mites

Fig. 33-31
Scorpion
Dust mite
Web-building spider
50 µm

Fig. 33-31c
Web-building spider

• Arachnids have an abdomen and a
cephalothorax, which has six pairs of
appendages, the most anterior of which are the
chelicerae
• Gas exchange in spiders occurs in respiratory
organs called book lungs
• Many spiders produce silk, a liquid protein,
from specialized abdominal glands

Fig. 33-32
Intestine
Heart
Digestive
gland
Ovary
Anus
Spinnerets
Silk gland
Gonopore
(exit for eggs) Sperm
receptacle
Book lung
Chelicera Pedipalp
Poison
gland
Eyes
Brain
Stomach

Myriapods
• Subphylum Myriapoda includes millipedes and
centipedes
– Myriapods are terrestrial, and have jaw-like
mandibles
• Millipedes, class Diplopoda, have many legs
– Each trunk segment has two pairs of legs

• Centipedes, class Chilopoda, are carnivores
– They have one pair of legs per trunk segment

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

Fig. 33-35
Abdomen Thorax Head
Compound eye
Antennae
Heart
Dorsal
artery Crop
Cerebral ganglion
Mouthparts
Nerve cords
Tracheal tubesOvary
Malpighian
tubules
Vagina
Anus

• Insects diversified several times following the
evolution of flight, adaptation to feeding on
gymnosperms, and the expansion of
angiosperms
• Insect and plant diversity declined during the
Cretaceous extinction, but have been
increasing in the 65 million years since

• 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

• 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

• 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
Video: Butterfly EmergingVideo: Butterfly Emerging

Fig. 33-36
a) Larva (caterpillar)
(b) Pupa
(c) Later-stage
pupa (d) Emerging
adult
(e) Adult

Fig. 33-36a
(a) Larva (caterpillar)

Fig. 33-36c
(c) Later-stage pupa

Fig. 33-36d
(d) Emerging adult

• Most insects have separate males and females
and reproduce sexually
• Individuals find and recognize members of their
own species by bright colors, sound, or odors
• Some insects are beneficial as pollinators,
while others are harmful as carriers of
diseases, or pests of crops
• Insects are classified into more than 30 orders
Video: Bee PollinatingVideo: Bee Pollinating

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
• Most crustaceans have separate males and
females

• Isopods include terrestrial, freshwater, and
marine species
– Pill bugs are a well known group of terrestrial
isopods
• Decapods are all relatively large crustaceans
and include lobsters, crabs, crayfish, and shrimp

Fig. 33-38
(a) Ghost crab
(b) Krill (c) Barnacles

• Planktonic crustaceans include many species
of copepods, which are among the most
numerous of all animals

• Barnacles are a group of mostly sessile
crustaceans
• They have a cuticle that is hardened into a
shell

Concept 33.5: 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
• Shared characteristics define deuterostomes
(Chordates and Echinoderms)
– Radial cleavage
– Formation of the mouth at the end of the
embryo opposite the blastopore

Fig. 33-UN5
Cnidaria
Lophotrochozoa
Ecdysozoa
Deuterostomia

Echinoderms
• Sea stars and most other echinoderms are
slow-moving or sessile marine animals
• A thin epidermis covers an endoskeleton of
hard calcareous plates
• Echinoderms have a unique water vascular
system, a network of hydraulic canals
branching into tube feet that function in
locomotion, feeding, and gas exchange
• Males and females are usually separate, and
sexual reproduction is external

Fig. 33-39
Anus
Stomach
Spine
Gills
Madreporite
Radial
nerve
Gonads
Ampulla
Podium
Tube
feet
Radial canal
Ring
canal
Central disk
Digestive glands

Video: Echinoderm Tube FeetVideo: Echinoderm Tube Feet
• 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)

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
• Sea stars can regrow lost arms

Fig. 33-40
(a) A sea star (class Asteroidea)
(c) A sea urchin (class Echinoidea)
(e) A sea cucumber (class Holothuroidea)
(b) A brittle star (class Ophiuroidea)
(d) A feather star (class Crinoidea)
(f) A sea daisy (class Concentricycloidea)

Fig. 33-40a
(a) A sea star (class Asteroidea)

Brittle Stars
• Brittle stars have a distinct central disk and
long, flexible arms, which they use for
movement

Fig. 33-40b
(b) 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

Fig. 33-40c
c) A sea urchin (class Echinoidea)

Sea Lilies and Feather Stars
• Sea lilies live attached to the substrate by a
stalk
• Feather stars can crawl using long, flexible
arms

Fig. 33-40d
(d) A feather star (class Crinoidea)

Sea Cucumbers
• Sea cucumbers lack spines, have a very
reduced endoskeleton, and do not look much
like other echinoderms
• Sea cucumbers have five rows of tube feet;
some of these are developed as feeding
tentacles

Fig. 33-40e
(e) A sea cucumber (class Holothuroidea)

Sea Daisies
• Sea daisies were discovered in 1986, and only
three species are known

Fig. 33-40f
(f) 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, but have
evolved separately for at least 500 million
years

You should now be able to:
1. Describe how a sponge feeds and digests its
food
2. List the characteristics of the phylum Cnidaria
that distinguish it from other animal phyla
3. List the four classes of Cnidaria and
distinguish among them based on life cycle
morphology
4. List the characteristics of Platyhelminthes and
distinguish among the four classes

5. Describe a lophophore and name two
lophophorate phyla
6. Describe the features of molluscs and
distinguish among the four classes
7. Describe the features of annelids and
distinguish among the three classes
8. List the characteristics of nematodes that
distinguish them from other wormlike animals

9. List three features that account for the
success of arthropods
10. Define and distinguish among the four major
arthropod lineages
11. Describe the developmental similarities
between echinoderms and chordates
12. Distinguish among the six classes of
echinoderms

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