The Animal Kingdom:
The Protostomes
Chapter 30
Learning Objective 1
•
Cite specific examples of the evolutionary
significance of the coelom
Coelom 1
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True coelom is a fluid-filled body cavity
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•
completely lined by mesoderm between
digestive tube and outer body wall
Allows tube-within-a-tube body plan
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•
body wall is outer tube
inner tube is digestive tube
Coelom 2
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An enclosed compartment (or series of
compartments) of fluid under pressure
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Serve as hydrostatic skeleton
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contracting muscles push against tube of fluid
Coelom 3
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A space in which internal organs develop
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including gonads
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Helps transport materials
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Protects internal organs
KEY CONCEPTS
•
Evolution of the coelom has been
associated with important innovations in
body plan, including cephalization, the
tube-within-a-tube body plan,
compartmentalization, and segmentation
Learning Objective 2
•
Characterize the protostomes
•
Describe their two main evolutionary
branches
•
Give examples of animals assigned to
each branch
Protostomes
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Characterized by
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spiral cleavage
determinate cleavage
development of mouth from blastopore
Two Branches of Protostomes
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Lophotrochozoa
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platyhelminths, nemerteans, mollusks,
annelids, lophophorate phyla, rotifers
Ecdysozoa
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nematodes (roundworms) and arthropods
KEY CONCEPTS
•
Protostomes are a monophyletic group
that gave rise to two major clades:
Lophotrochozoa and Ecdysozoa
Learning Objective 3
•
What are the distinguishing characteristics
of phylum Nemertea and phylum
Platyhelminthes?
•
Describe the main classes of phylum
Platyhelminthes, giving examples of
animals that belong to each class
Phylum Nemertea (Ribbon Worms) 1
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Characterized by proboscis
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•
muscular tube for capturing food, defense
Reduced coelom (rhynchocoel)
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space surrounding proboscis
Phylum Nemertea (Ribbon Worms) 2
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Nemerteans have
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•
tube-within-a-tube body plan
complete digestive tract with mouth and anus
a circulatory system
Nemerteans
Phylum Platyhelminthes
(Flatworms) 1
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Acoelomate animals with
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bilateral symmetry
cephalization
3 definite tissue layers
well-developed organs
Many are hermaphrodites
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single animal produces both sperm and eggs
Phylum Platyhelminthes
(Flatworms) 2
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Ladder-type nervous system
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•
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sense organs
simple brain composed of two ganglia
2 nerve cords that extend the length of body
Protonephridia
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function in osmoregulation and disposal of
metabolic wastes
3 Classes of
Phylum Platyhelminthes
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Class Turbellaria
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Classes Trematoda and Monogenea
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free-living flatworms, including planarians
parasitic flukes
Class Cestoda
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parasitic tapeworms
Planarian
Deuterostomia
Ecdysozoa
Rotifera
Lophophorate
phyla
Annelida
Mollusca
Nemertea
Platyhelminthes
Radiata
Parazoa
Lophotrochozoa
Choanoflagellate
ancestor
Fig. 30-1 (1), p. 642
Ganglia
Auricle
Auricle
Eyespot
Nerve
Gastrovascular
cavity
Pharynx
Sheath
surrounding
pharynx
Mouth
1 mm
Fig. 30-1ab, p. 642
Pharyngeal
sheath
cavity
Pharyngeal
cavity
Inner
muscle
layer of
pharynx
Outer
muscle
layer
Muscle
Epidermis
Sperm
mass
Ventral
nerve
cords
Adhesive
gland
Cilia
Muscle
layers
Body wall
composed of
epidermis,
circular muscle, and
longitudinal muscle
Fig. 30-1c, p. 642
Insert “Planarian organ
systems”
planarian_organs_v2.swf
Parasitic Flukes and Tapeworms
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Typically have suckers or hooks
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for holding on to their hosts
Have complicated life cycles
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intermediate hosts
large numbers of eggs
Parasitic Fluke
2 Larvae make their way to
circulatory system, where they
mature. During reproduction,
which takes place in veins, male
holds female in a long groove.
1 Larvae
burrow
through
skin.
1 mm
3 Eggs pass
into
intestine.
7 Finally, forktailed larvae
(cercariae)
develop and
leave snail.
4 Eggs containing
developing embryos are
excreted with feces.
6 Larvae must enter a second
host, a freshwater snail. After
burrowing into tissues of snail,
larvae develop into a form that
reproduces asexually.
5 If they find their way
to fresh water, the
eggs hatch, releasing
free-swimming larvae
(miracidia).
Fig. 30-2, p. 644
Tapeworm
Insert “Blood fluke lifecycle” and “Tapeworm life
cycle”
blood_fluke.swf
tapeworm.swf
Watch the fluke and tapeworm
life cycles by clicking on the
figures in ThomsonNOW.
Learning Objective 4
•
What are the adaptive advantages of
cephalization?
Cephalization
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Evolution of a head
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concentration of sense organs and nerve cells
(simple brain) at anterior end
(Flatworms show beginnings of cephalization)
Increases effectiveness of bilateral animal
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to actively find food, shelter, mates
to detect enemies
Learning Objective 5
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What are the distinguishing characteristics
of phylum Mollusca and the four molluscan
classes discussed?
•
Give examples
Phylum Mollusca
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Soft-bodied animals
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Ventral foot
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usually covered by a shell
for locomotion
Mantle
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covers visceral mass (body organs)
Mollusks
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Most have open circulatory system
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Most have rasplike radula for feeding
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Cephalopods have closed circulatory system
Bivalves are suspension feeders
Most marine mollusks have freeswimming, ciliated trochophore larva
Insert “Molluscan
classes”
mollusk_classes.swf
Trochophore Larva
Digestive
tract
Cilia
Mouth
Nephridium
Mesodermal
cells
Anus
Fig. 30-7, p. 648
Class Polyplacophora
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•
Includes marine chitons
Shells consist of 8 overlapping plates
Shell
Digestive
tract
Class Polyplacophora
Fig. 30-6a, p. 647
Class Gastropoda
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Largest group of mollusks
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snails, slugs, and their relatives
Body undergoes torsion
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a twisting of the visceral mass
Shell
Foot
Digestive
tract
Class Gastropoda
Fig. 30-6b, p. 647
Insert “Snail body plan”
snail_body_plan.swf
Torsion
Insert “Torsion in
gastropods”
torsion.swf
Class Bivalvia
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Includes aquatic clams, scallops, oysters
•
Two-part shell
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hinged dorsally
encloses bodies
Suspension feeders
Shell
Digestive
Foot tract
Class Bivalva
Fig. 30-6c, p. 647
Clam
Heart
Digestive gland
Stomach
DORSAL
Metanephridium
Intestine
Esophagus
Posterior
adductor muscle
Anus
Ganglion
Anterior adductor
muscle
Excurrent
siphon
Incurrent
siphon
Mouth
Palp
Pedal
ganglion
Gill—partially
cut
Mantle
Foot
Shell
Intestine Gonad
VENTRAL
Fig. 30-10, p. 649
Insert “Clam body plan”
clam.swf
Class Cephalopoda
•
Includes squids, octopods, Nautilus
•
Active, predatory swimmers
•
Tentacles surround the mouth
•
located in the large head
Tentacles
(modified
foot)
Internal
shell
Digestive
tract
Class Cephalopoda
Fig. 30-6d, p. 647
Learning Objective 6
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What are the distinguishing characteristics
of phylum Annelida and the three annelid
classes discussed?
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Give examples
Phylum Annelida
(Segmented Worms)
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Aquatic worms, earthworms, leeches
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Conspicuously long bodies
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Segmentation
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both internally and externally
Large, compartmentalized coelom
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serves as hydrostatic skeleton
Annelids
Mouth
Setae
Clitellum
Suckers
Parapodia
Anus
Class Polychaeta
Class Oligochaeta
Class Hirudinea
Fig. 30-11 (a-c), p. 650
Setae
Deuterostomia
Ecdysozoa
Rotifera
Lophophorate
phyla
Annelida
Mollusca
Nemertea
Platyhelminthes
Radiata
Parazoa
Lophotrochozoa
Mouth
Clitellum
Suckers
Parapodia
Choanoflagellate
ancestor
Anus
Class Polychaeta
Class Oligochaeta Class Hirudinea
Stepped Art
Fig. 30-11 (a-c), p. 650
Earthworm
Clitellum
Intestine
Gizzard Crop
Esophagus
Pharynx
Dorsal vessel
Ventral vessel
Muscles
Longitudinal
Circular
Septa
Nerve cord
Mouth
Cerebral
ganglia
Fig. 30-12a, p. 651
Intestine
Dorsal
blood
vessel
Metanephridia
Coelom
Ventral
blood
vessel
Nerve cord
Fig. 30-12b, p. 651
Insert “Earthworm body
plan”
earthworm_v2.swf
Leeches
Class Polychaeta
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Marine worms with parapodia
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appendages for locomotion, gas exchange
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Parapodia have many setae
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Well-defined head with sense organs
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unlike other annelids
Class Oligochaeta
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Earthworms
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Characterized by few short setae per
segment
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Body divided into > 100 segments
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separated internally by septa
Class Hirudinea
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Leeches
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Characterized by absence of setae and
appendages
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Parasitic leeches have suckers
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for holding on to their host
Learning Objective 7
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What are the distinguishing characteristics
of the lophophorate phyla?
The Lophophorate Phyla
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Marine animals with a lophophore
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brachiopods, phoronids, bryozoans
Lophophore
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ciliated ring of tentacles surround the mouth
specialized to capture particles in water
Lophophorates
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Phylum Brachiopoda
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Phylum Phoronida
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Phylum Bryozoa
Deuterostomia
Ecdysozoa
Rotifera
Lophophorate
phyla
Annelida
Mollusca
Nemertea
Platyhelminthes
Radiata
Parazoa
Lophotrochozoa
Choanoflagellate
ancestor
Fig. 30-14 (1), p. 653
Phylum Rotifera
Deuterostomia
Ecdysozoa
Rotifera
Lophophorate
phyla
Annelida
Mollusca
Nemertea
Platyhelminthes
Radiata
Parazoa
Lophotrochozoa
Choanoflagellate
ancestor
Fig. 30-15 (1), p. 654
150 µm
Fig. 30-15a, p. 654
Crown of
cilla
Mouth
Eyespot
Pharynx (grinding
organ)
Digestive
glands
Stomach
Reproductive
organ
Protonephridium
Intestine
Bladder
Anus
Cuticle and
epidermis
Fig. 30-15b, p. 654
Learning Objective 8
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What are the distinguishing characteristics
of phylum Nematoda?
Phylum Nematoda (Roundworms)
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Highly successful ecdysozoans
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Pseudocoelom
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Body covered by tough cuticle
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helps prevent desiccation
Phylum Nematoda (Roundworms)
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Parasitic nematodes in humans
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Ascaris
hookworms
trichina worms
pinworms
Ascaris
Mouth
Pharynx
Dorsal nerve
Excretory
canal
Excretory
gland
Pharynx
Muscle of
pharynx
wall
Pseudocoelom
Uterus
Ovary
Intestine
Excretory
canal
Vulva
Muscle layer
Ventral nerve
Epidermis
Cuticle
(b) Cross section
Anus
(a) Longitudinal section
Fig. 30-17, p. 656
Learning Objective 9
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What are the distinguishing characteristics
of phylum Arthropoda?
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Distinguish among the subphyla and
classes of this phylum
•
Give examples of animals that belong to
each group
Phylum Arthropoda 1
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Segmented animals with paired, jointed
appendages
•
Armorlike exoskeleton of chitin
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Molting necessary for arthropod to grow
Phylum Arthropoda 2
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Open circulatory system
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dorsal heart, pumps hemolymph
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Aquatic forms have gills for gas exchange
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Terrestrial forms have either tracheae or
book lungs
KEY CONCEPTS
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The most biologically successful
protostomes in terms of diversity and
numbers are the mollusks and the
arthropods
Trilobites
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Extinct marine arthropods
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covered by hard, segmented shell
Each segment had a pair of biramous
appendages with two jointed branches
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inner walking leg
outer gill branch
Trilobites
Deuterostomia
Arthropoda
Nematoda
Lophotrochozoa
Radiata
Parazoa
Ecdysozoa
Choanoflagellate
ancestor
Fig. 30-19 (1), p. 658
Antenna
Head
Eye
Gill
Lateral lobe
Median lobe
(a) Dorsal view of a trilobite.
(b) Ventral view.
Fig. 30-19ab, p. 658
Subphylum Myriapoda
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2 Classes
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Chilopoda (centipedes)
Diplopoda (millipedes)
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Uniramous (unbranched) appendages
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Single pair of antennae
Myriapods
Subphylum Chelicerata 1
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Merostomes (horseshoe crabs) and
Arachnids (spiders, mites, and relatives)
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Body with cephalothorax and abdomen
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6 pairs of uniramous, jointed appendages
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4 pairs serve as legs
Subphylum Chelicerata 2
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First appendages are chelicerae
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second are pedipalps
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Appendages adapted for manipulation of
food, locomotion, defense, copulation
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No antennae, no mandibles
Chelicerates
Subphylum Crustacea 1
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Lobsters, crabs, shrimp, pill bugs,
barnacles
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Body with cephalothorax and abdomen
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Most have five pairs of walking legs
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Appendages are biramous
Subphylum Crustacea 2
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Two pairs of antennae
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Third appendages are mandibles
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sense taste and touch
for chewing
Two pairs of maxillae
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posterior to mandibles
manipulate and hold food
Crustaceans
Lobster
Cephalothorax
Abdomen Thorax
Head
Eye
Fifth
walking leg
Fig. 30-23a, p. 661
Tail fan
Fifth
walking leg
Second
walking
leg
Mouth
Third
maxilliped
Cheliped
First
antenna
Second
antenna
Swimmerets First
swimmeret
(used by male
in copulation)
Fig. 30-23b, p. 661
Subphylum Hexapoda
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Includes class Insecta
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articulated, tracheated hexapods
Head
Thorax
Abdomen
Forewing
Antenna
Simple eye
Compound eye
Sound receptor
Spiracles
Hindwing
(a) External structure. Note the three pairs of segmented legs.
Fig. 30-24a, p. 661
Insects
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•
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Body with head, thorax, and abdomen
Uniramous appendages
Single pair of antennae
Tracheae for gas exchange
Malpighian tubules for excretion
Grasshopper
Ovary
Digestive gland
Heart
Anus
Brain
Nerve cord
Malpighian tubules
(b) Internal Anatomy.
Intestine
Genital opening
Learning Objective 10
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What adaptations have contributed to the
biological success of insects?
Insect Adaptations 1
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Versatile exoskeleton
Segmentation
Specialized jointed appendages
Highly developed sense organs
Ability to fly
Insert “Insect head parts”
insect_heads.swf
Insect Adaptations 2
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Metamorphosis
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transition from one developmental form to
another
reduces intraspecific competition
Metamorphosis
Insert “Insect
development”
insect_devt.swf
Insect Adaptations 3
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Insects have developed
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effective reproductive strategies
effective mechanisms for defense, offense
ability to communicate
KEY CONCEPTS
•
The remarkable biological success of the
insects can be attributed to the evolution
of complex body plans and life cycles, for
example, their exoskeleton, segmentation,
specialized jointed appendages, ability to
fly, and metamorphosis
Explore the body plans of the
protostomes by clicking on the
figures in ThomsonNOW.