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LECTURE PRESENTATIONS
For CAMPBELL BIOLOGY, NINTH EDITION
Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson
Chapter 33
An Introduction to Invertebrates
Lectures by
Erin Barley
Kathleen Fitzpatrick
© 2011 Pearson Education, Inc.
Overview: Life Without a Backbone
• Invertebrates are animals that lack a backbone
• They account for 95% of known animal species
• They are morphologically diverse
– For example, the Christmas tree worm
(Spirobranchus giganteus) has tentacles for gas
exchange and feeding
© 2011 Pearson Education, Inc.
Figure 33.1
Figure 33.3a
Porifera (5,500 species)
Placozoa (1 species)
0.5 mm
A sponge
Cnidaria (10,000 species)
A placozoan (LM)
Ctenophora (100 species)
A jelly
Acoela (400 species)
1.5 mm
Acoel flatworms (LM)
A ctenophore, or comb jelly
Figure 33.3b
Platyhelminthes
(20,000 species)
Rotifera
(1,800 species)
0.1 mm
Ectoprocta
(4,500 species)
Ectoprocts
A marine flatworm
Acanthocephala
(1,100 species)
Nemertea
(900 species)
Brachiopoda
(335 species)
A brachiopod
A rotifer (LM)
Annelida
(16,500 species)
Cycliophora
(1 species)
Curved
hooks
100 m
An acanthocephalan (LM)
Mollusca
(93,000 species)
A ribbon worm
An octopus
A cycliophoran
(colorized SEM)
Lophotrochozoa
A marine annelid
Figure 33.3c
Loricifera (10 species)
Priapula (16 species)
Onychophora (110 species)
50 m
A loriciferan (LM)
A priapulan
An onychophoran
Nematoda
(25,000 species)
Tardigrada
(800 species)
Arthropoda
(1,000,000 species)
100 m
A roundworm
(colored SEM)
Ecdysozoa
Tardigrades
(colorized SEM)
A scorpion (an arachnid)
Figure 33.3d
Hemichordata
(85 species)
Chordata
(52,000 species)
A tunicate
Echinodermata (7,000 species)
An acorn worm
Deuterostomia
A sea urchin
Concept 33.1: Sponges are basal animals
that lack true tissues
• Animals in the phylum Porifera are known
informally as sponges
• They are sedentary and live in marine waters or
fresh water
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• Sponges are suspension feeders, capturing food
particles suspended in the water that passes
through their body
• Water is drawn through pores into a cavity called
the spongocoel and out through an opening
called the osculum
• Sponges lack true tissues and organs
© 2011 Pearson Education, Inc.
Figure 33.4
Azure vase sponge
(Callyspongia
plicifera)
Food particles
in mucus
Flagellum
Choanocyte
Collar
Choanocyte
Osculum
Phagocytosis of
food particles
Amoebocyte
Spongocoel
Pore
Spicules
Epidermis
Mesohyl
Water
flow
Amoebocytes
• Choanocytes, flagellated collar cells, generate a
water current through the sponge and ingest
suspended food
• Sponges consist of a gelatinous 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
© 2011 Pearson Education, Inc.
• Cnidarians have diversified into a wide range of
both sessile and motile forms including jellies,
corals, and hydras
• They exhibit a relatively simple 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
© 2011 Pearson Education, Inc.
• There are two variations on the body plan: the
sessile polyp and motile medusa
• A polyp adheres to the substrate by the aboral
end of its body
• A medusa has a bell-shaped body with its mouth
on the underside
• Medusae do not attach to the substate but move
freely
© 2011 Pearson Education, Inc.
Figure 33.5
Mouth/anus
Tentacle
Gastrovascular
cavity
Gastrodermis
Mesoglea
Body
stalk
Epidermis
Tentacle
Polyp
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
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Figure 33.6
Tentacle
Cuticle
of prey
Thread
Nematocyst
“Trigger”
Thread
discharges
Cnidocyte
Thread
(coiled)
• Phylum Cnidaria is divided into four major classes
–
–
–
–
Hydrozoa
Scyphozoa
Cubozoa
Anthozoa
© 2011 Pearson Education, Inc.
Figure 33.7
(b) Scyphozoa
(a) Hydrozoa
(c) Cubozoa
(d) Anthozoa
Hydrozoans
• Most hydrozoans alternate between polyp and
medusa forms
• Hydra, a freshwater cnidarian, exists only in polyp
form and reproduces asexually by budding
© 2011 Pearson Education, Inc.
Figure 33.8-3
Feeding
polyp
Reproductive
polyp
Medusa
bud
MEIOSIS
Gonad
Medusa
Egg
ASEXUAL
REPRODUCTION
(BUDDING)
Portion
of a
colony
of polyps
SEXUAL
REPRODUCTION
FERTILIZATION
Developing
polyp
1 mm
Sperm
Mature
polyp
Zygote
Planula
(larva)
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 box-shaped and
has complex eyes
• Cubozoans often have highly toxic cnidocytes
© 2011 Pearson Education, Inc.
Anthozoans
• Class Anthozoa includes the corals and sea
anemones, and these cnidarians occur only as
polyps
• Corals often form symbioses with algae and
secrete a hard external skeleton
© 2011 Pearson Education, Inc.
• Lophotrochozoa 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
© 2011 Pearson Education, Inc.
Flatworms
• Members of phylum Platyhelminthes live in
marine, freshwater, and damp terrestrial habitats
• Flatworms are acoelomates
• They are flattened dorsoventrally and have a
gastrovascular cavity with one opening
• Gas exchange takes place across the surface, and
protonephridia regulate the osmotic balance
© 2011 Pearson Education, Inc.
• Flatworms are divided into two lineages
– Catenulida, or “chain worms,” reproduce asexually
by budding
– Rhabditophora are more diverse and include both
free-living and parasitic species
© 2011 Pearson Education, Inc.
Figure 33.9
5 mm
Free-Living Species
• The best-known rhabditophorans are planarians
• Planarians live in fresh water and prey on smaller
animals
• Planarians have light-sensitive eyespots and
centralized nerve nets
© 2011 Pearson Education, Inc.
• 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
© 2011 Pearson Education, Inc.
Figure 33.10
Gastrovascular cavity
Pharynx
Gastrovascular
cavity
Mouth
Eyespots
Ventral nerve cords
Ganglia
Parasitic Species
• Parasitic rhabditophorans live in or on other
animals
• Two important groups of parasitic rhabditophorans
are the trematodes and the tapeworms
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Trematodes
• Trematodes 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
• They produce surface proteins that mimic their
host and release molecules that manipulate the
host’s immune system
© 2011 Pearson Education, Inc.
Figure 33.11
Male
Human
host
Female
1 mm
Mature flukes
Ciliated
larva
Motile
larva
Snail host
Tapeworms
• Tapeworms are parasites of vertebrates and
lack a digestive system
• Tapeworms absorb nutrients from the host’s
intestine
© 2011 Pearson Education, Inc.
• The scolex contains suckers and hooks for
attaching to the host
• Proglottids are units that contain sex organs and
form a ribbon behind the scolex
• Fertilized eggs, produced by sexual reproduction,
leave the host’s body in feces
© 2011 Pearson Education, Inc.
Figure 33.12
100 m
Hooks
Sucker
Proglottids with
reproductive
structures
Scolex
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
© 2011 Pearson Education, Inc.
Figure 33.13
Jaws
Anus
Stomach
Crown
of cilia
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
© 2011 Pearson Education, Inc.
Lophophorates: Ectoprocts and Brachiopods
• Lophophorates have a lophophore, a crown of
ciliated tentacles around their mouth
• Lophophorates have a true coelom
• Lophophorates include two phyla: Ectoprocta and
Brachiopoda
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• Ectoprocts (also called bryozoans) are sessile
colonial animals that superficially resemble plants
• A hard exoskeleton encases the colony, and
some species are reef builders
© 2011 Pearson Education, Inc.
Figure 33.14
Lophophore
(a) Ectoprocts, colonial
lophophorates
Lophophore
(b) Lampshell,
a brachiopod
• 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
• Brachiopods are marine and attach to the seafloor
by a stalk
© 2011 Pearson Education, Inc.
Figure 33.14b
Lophophore
(b) Lampshell,
a brachiopod
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 snails and slugs 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
• Many molluscs also have a water-filled mantle
cavity and feed using a rasplike radula
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Figure 33.15
Nephridium
Heart
Visceral mass
Coelom
Digestive tract
Intestine
Gonads
Mantle
Stomach
Shell
Radula
Mantle
cavity
Mouth
Anus
Gill
Foot
Nerve
cords
Esophagus
Mouth
Radula
• Most molluscs have separate sexes with gonads
located in the visceral mass, but many snails are
hermaphrodites
• The life cycle of many molluscs includes a ciliated
larval stage called a trochophore
© 2011 Pearson Education, Inc.
• Four of the major classes of molluscs are
–
–
–
–
Polyplacophora (chitons)
Gastropoda (snails and slugs)
Bivalvia (clams, oysters, and other bivalves)
Cephalopoda (squids, octopuses, cuttlefish, and
chambered nautiluses)
© 2011 Pearson Education, Inc.
Chitons
• Chitons are oval-shaped marine animals encased
in an armor of eight dorsal plates
• They use their foot like a suction cup to grip rock,
and their radula to scrape algae off the rock
surface
© 2011 Pearson Education, Inc.
Figure 33.16
Gastropods
• About three-quarters of all living species of
molluscs are gastropods
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Figure 33.17
(a) A land snail
(b) A sea slug (nudibranch)
• Most gastropods are marine, but many are
freshwater and terrestrial species
• The most distinctive characteristic of gastropods is
torsion, which causes the animal’s anus and
mantle to end up above its head; torsion is
different from the coiling of a shell
• Most have a single, spiraled shell
• Slugs lack a shell or have a reduced shell
© 2011 Pearson Education, Inc.
Figure 33.18
Mantle
cavity
Anus
Mouth
Stomach
Intestine
Bivalves
• Bivalves are marine and include many species of
clams, oysters, mussels, and scallops
• They have a shell divided into two halves drawn
together by adductor muscles
• Some bivalves have eyes and sensory tentacles
along the edge of their mantle
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Figure 33.19
• The mantle cavity of a bivalve contains gills that
are used for feeding as well as gas exchange
© 2011 Pearson Education, Inc.
Figure 33.20
Mantle
Hinge area
Coelom
Gut
Heart
Digestive
gland
Adductor muscle
(one or two)
Anus
Mouth
Excurrent
siphon
Shell
Palp
Foot
Mantle
cavity
Gonad
Gill
Water
flow
Incurrent
siphon
Cephalopods
• Cephalopods are carnivores with beak-like jaws
surrounded by tentacles of their modified foot
• Most octopuses creep along the sea floor in
search of prey
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Figure 33.21
Squid
Octopus
Chambered
nautilus
• Squids use their siphon to fire a jet of water, which
allows them to swim very quickly
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Figure 33.21b
Octopus
• One small group of shelled cephalopods, the
nautiluses, survives today
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Figure 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 65.5 million years ago
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Protecting Freshwater and Terrestrial
Molluscs
• Molluscs are the animal group with the largest
number of recent extinctions
• The most threatened groups are
– Freshwater bivalves, including pearl mussels
– Terrestrial gastropods, including Pacific island
land snails
• These molluscs are threatened by habitat loss,
pollution, and non-native species
© 2011 Pearson Education, Inc.
Figure 33.22
Other invertebrates
Molluscs
Amphibians
Insects
Birds
Fishes
Mammals
An endangered Pacific
island land snail,
Partula suturalis
Recorded extinctions of animal
species (Data: International Union for
Reptiles
(excluding
birds)
Conservation of Nature, 2008)
Workers on a mound of pearl
mussels killed to make buttons
(ca. 1919)
Annelids
• Annelids have bodies composed of a series of
fused rings
• Annelids are coelomates
• The phylum Annelida is divided into two groups
– Polychaeta (polychaetes)
– Oligochaeta (earthworms and their relatives, and
leeches)
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Polychaetes
• Members of class Polychaetes have paddle-like
parapodia that work as gills and aid in locomotion
• Most polychaetes are marine
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Figure 33.23
Parapodia
Oligochaetes
• Oligochaetes (class Oligochaeta) are named for
relatively sparse chaetae, bristles made of chitin
© 2011 Pearson Education, Inc.
Earthworms
• Earthworms eat through soil, extracting nutrients
as the soil moves through the alimentary canal
• Earthworms are hermaphrodites but cross-fertilize
• Some reproduce asexually by fragmentation
© 2011 Pearson Education, Inc.
Figure 33.24
Cuticle
Coelom
Epidermis
Septum (partition
between segments)
Circular muscle
Metanephridium
Longitudinal muscle
Anus
Dorsal vessel
Chaetae
Intestine
Skin
Ventral vessel
Fused
nerve cords
Nephrostome
Metanephridium
Clitellum
Esophagus Crop
Pharynx
Intestine
Giant Australian earthworm
Gizzard
Cerebral
ganglia
Mouth
Subpharyngeal
ganglion
Circulatory
system vessels
Ventral nerve cords
with segmental
ganglia
Leeches
• Most species of leeches live in fresh water; some
are marine or terrestrial
• Leeches include predators of invertebrates, and
parasites that suck blood
• Leeches secrete a chemical called hirudin to
prevent blood from coagulating
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Figure 33.25
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
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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
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Figure 33.26
25 m
• Caenorhabditis elegans is a model organism in
research
• Some species of nematodes are important
parasites of plants and animals
• Thrichinella spiralis can be acquired by humans
from undercooked pork
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Figure 33.27
Encysted juveniles
Muscle tissue
50 m
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
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Arthropod Origins
• The arthropod body plan consists of a segmented
body, hard exoskeleton, and jointed appendages
• This body plan dates to the Cambrian explosion
(535–525 million years ago)
• Early arthropods show little variation from segment
to segment
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Figure 33.28
General Characteristics of Arthropods
• The appendages of some living arthropods are
modified for functions such as walking, feeding,
sensory reception, reproduction, and defense
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Figure 33.30
Cephalothorax
Antennae
(sensory
reception)
Abdomen
Thorax
Head
Swimming appendages (one pair per
abdominal segment
Pincer
(defense)
Mouthparts
(feeding)
Walking legs
• 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
© 2011 Pearson Education, Inc.
• Arthropods have eyes, olfactory receptors, and
antennae that function in touch and smell
• Arthropods have an open circulatory system in
which 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
– Chelicerates (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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Chelicerates
• Chelicerates, subphylum Chelicerata, 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
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Figure 33.31
• Most modern cheliceriforms are arachnids, which
include spiders, scorpions, ticks, and mites
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Figure 33.32
50 m
Scorpion
Dust mite
Web-building
spider
• Arachnids have an abdomen and a cephalothorax,
which has six pairs of appendages: the chelicerae,
the pedipalps, and four pairs of walking legs
• Gas exchange in spiders occurs in respiratory
organs called book lungs
• Many spiders produce silk, a liquid protein, from
specialized abdominal glands
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Figure 33.33
Stomach
Intestine
Heart
Brain
Digestive
gland
Eyes
Ovary
Poison
gland
Anus
Book lung
Spinnerets
Silk gland
Gonopore
(exit for eggs)
Sperm
receptacle
Chelicera
Pedipalp
Myriapods
• Subphylum Myriapoda includes millipedes and
centipedes
• Myriapods are terrestrial, and have jaw-like
mandibles
• Millipedes eat decaying leaves and plant matter
• Millipedes have many legs, with two pairs per
trunk segment
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Figure 33.34
(a) Millipede
(b) Centipede
• Centipedes are carnivores
• Centipedes 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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Figure 33.35
Abdomen
Thorax Head
Compound eye
Antennae
Heart
Dorsal
artery
Crop
Anus
Vagina
Malpighian
tubules
Ovary
Tracheal tubes
Nerve cords
Mouthparts
Cerebral
ganglion
• 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 has been increasing in
the 65 million years since
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• 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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Figure 33.36
• 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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Figure 33.37
(a) Larva (caterpillar)
(b) Pupa
(c) Later-stage
(d) Emerging
pupa
adult
(e) 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
© 2011 Pearson Education, Inc.
Figure 33.38
Archaeognatha (bristletails; 350 species)
Thysanura (silverfish; 450 species)
Winged insects (many orders)
Complete metamorphosis
Coleoptera
(beetles; 350,000 species)
Diptera
(151,000 species)
Hymenoptera
(125,000 species)
Proboscis
Lepidoptera
(120,000 species)
Incomplete metamorphosis
Hemiptera
(85,000 species)
Orthoptera
(13,000 species)
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
• Small crustaceans exchange gases through the
cuticle; larger crustaceans have gills
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• 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
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Figure 33.39
(a) Ghost crab
(b) Krill
(c) Barnacles
• Planktonic crustaceans include many species of
copepods, which are among the most numerous
of all animals
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• Barnacles are a group of mostly sessile
crustaceans
• They have a cuticle that is hardened into a shell
© 2011 Pearson Education, Inc.
Concept 33.5: Echinoderms and chordates
are deuterostomes
• Echinoderms (phylum Echinodermata) include sea
stars and sea urchins
• Chordates (phylum Chordata) include the
vertebrates
• Echinoderms and chordates constitute the clade
Deuterostomia
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• Deuterostomes share developmental
characteristics
– Radial cleavage
– Formation of the anus from the blastopore
• However, some other animals also share these
developmental characteristics
• Deuterostomes are defined primarily by DNA
similarities
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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 and
feeding
• Males and females are usually separate, and
sexual reproduction is external
© 2011 Pearson Education, Inc.
Figure 33.40
Short digestive tract
Stomach
Anus
Spine
Gills
Central disk
Madreporite
Digestive glands
Radial
nerve
Ring
canal
Radial canal
Gonads
Ampulla
Podium
Tube feet
• Most adult echinoderms have radial symmetry with
multiples of five
• Echinoderm larvae have bilateral symmetry
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• Living echinoderms are divided into five classes
– Asteroidea (sea stars and sea daisies)
– Ophiuroidea (brittle stars)
– Echinoidea (sea urchins and sand dollars)
– Crinoidea (sea lilies and feather stars)
– Holothuroidea (sea cucumbers)
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Asteroidea: Sea Stars and Sea Daisies
• Sea stars have multiple arms radiating from a
central disk
• The undersurface of each arm bears tube feet,
which grip substrate with adhesive chemicals
• Sea stars feed on bivalves by prying them open
with their tube feet, everting their stomach, and
digesting their prey externally with digestive
enzymes
• Sea stars can regrow lost arms
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• Sea daisies were discovered in 1986, and only
three species are known
• Sea daisies live on submerged wood and absorb
nutrients through a membrane that surrounds their
body
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Figure 33.41
Ophiuroidea: Brittle Stars
• Brittle stars have a distinct central disk and long,
flexible arms, which they use for movement
• Some species are suspension feeders, while
others are predators or scavengers
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Figure 33.42
Echinoidea: Sea Urchins and Sand Dollars
• Sea urchins and sand dollars have no arms but
have five rows of tube feet
• Their spines are used for locomotion and
protection
• Sea urchins feed on seaweed using a jaw-like
structure on their underside
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Figure 33.43
Crinoidea: Sea Lilies and Feather Stars
• Sea lilies live attached to the substrate by a stalk
• Feather stars can crawl using long, flexible arms
• Both are suspension feeders
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Figure 33.44
Holothuroidea: 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
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Figure 33.45
Chordates
• Phylum Chordata consists of two subphyla of
invertebrates as well as hagfishes and vertebrates
• Chordates are bilaterally symmetrical coelomates
with segmented bodies
• Chordates share many features of embryonic
development with echinoderms, but have evolved
separately for at least 500 million years
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Figure 33.UN06