1. 30.3 The Trochozoa
Bilaterally symmetrical at least in some stage of their development
As embryos, they have three germ layers
As adults, they have the organ level of organization
Protostomes
Trochophores
Flatworms, rotifers, molluscs, and annelids
Either have trochophore larvae today or an ancestor had one on the past
cilia
trochophore larva

2. Page 627 cilia trochophore larva
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cilia
trochophore larva

3. 30.3 The Trochozoa Flatworms: Phylum Platyhelminthes
Incomplete digestive tract and only one opening, the mouth
No body cavity – mesoderm fills spaces between organs
Free-living planarians
Have muscles and excretory, reproductive, and digestive systems. They have all organs except respiratory and circulatory organs (diffusion).
The flat body facilitates diffusion of oxygen and other molecules from cell to cell.
Parasitic flukes and tapeworms

4. 30.3 The Trochozoa Free-living Flatworms Freshwater planarians
Found in lakes, ponds, and streams
Feed on small organisms such as worms and crustaceans
Possesses an excretory system (flame cell system)
Ladder-like nervous system exhibits cephalization
Reproduce both asexually and sexually
Regeneration (asexual)
Hermaphroditic cross-fertilization (sexual)

5. Planarian Anatomy gastrovascular cavity eyespots
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
gastrovascular cavity
eyespots
pharynx extended through mouth
auricle
a. Digestive system: Three-branched
system

6. © Tom E. Adams/Peter Arnold
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Planarian Anatomy
gastrovascular cavity
eyespots
pharynx extended through mouth
auricle
flame cell
fluid
cilia
a. Digestive system: Three-branched
system
flame cell
excretory canal
excretory pore
b. Excretory system: Flame-cell system
ovary
yolk
gland
sperm
duct
testis
genital pore
c. Reproductive system: Hermaphroditic system
brain
lateral nerve cord
transverse nerve
d. Nervous system: Ladder-style system
auricle
eyespots
© Tom E. Adams/Peter Arnold e.
5 mm 6

7. 30.3 The Trochozoa Parasitic Flatworms Primary and secondary hosts
Tapeworms (class Cestoda)
Endoparasites
Range in length from several millimeters to 20 meters
Tough outer tegument to protect from host’s enzymes
Scolex - has hooks for attachment; not a sucker
Body of segments called proglottids
Organs of both sexes in each proglottid
Proglottids filled with fertilized eggs are called gravid
Primary and secondary hosts

8. Life Cycle of a Tapeworm, Taenia
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
hooks
proglottid
scolex
sucker
2. Bladder worm attaches
to human intestine
where it matures into a
tapeworm.
1.0 mm
250 m
3. As the tapeworm grows, proglottids mature, and eventually fill with eggs.
4. Eggs leave the
primary host in
feces, which may
contaminate water
or vegetation.
5. Livestock may ingest the eggs,
becoming a secondary host as
each larva becomes a bladder
worm encysted in muscle.
6. Rare or uncooked meat
from secondary host contains
many bladder worms.
1. Primary host ingests meat
containing bladder worms.
(proglottid): © John D. Cunningham/Visuals Unlimited; (scolex): © James Webb/Phototake

9. 30.3 The Trochozoa Parasitic Flatworms Flukes (class Trematoda)
Endoparasites of various vertebrates
Blood, liver and lung flukes
Two suckers: one for feeding, one for attachment
Alimentary canal is well developed
Muscles and excretory system much like free-living flatworms
Poorly developed senses
Hermaphroditic
Complex life cycle involving two intermediate hosts

10. Schistosomiasis
Schistosomiasis, an infection of humans caused by blood flukes, is an extremely prevalent disease in Egypt – especially since the building of the Aswan High Dam. Standing water in irrigation ditches, combined with unsanitary practices, has created the conditions for widespread infection.

11. 30.3 The Trochozoa Molluscs (phylum Mollusca)
Second most numerous animal phylum
Includes chitons, limpets, slugs, snails, abalones, conchs, nudibranchs, clams, scallops, squid, and octopuses
True coelom
Bilateral symmetry
3 germ layers
Organ level of organization
Complete digestive tract

12. 30.3 The Trochozoa Molluscs Unique characteristics of molluscs
Three distinct parts:
Visceral mass: includes most organs
Foot: muscular portion used for locomotion
Mantle: covering that almost encloses visceral mass
Mantle cavity - space between the two folds of the mantle
Mantle may secrete a shell
Radula - rasping organ for feeding

13. Diversity of Molluscs shell eyes tentacles on mantle valve
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
shell
eyes
tentacles
on mantle
valve
b. Scallop, Pecten sp.
eye
tentacle
gills
arm
mantle
foot
suckers
c. Nudibranch, Glossodoris macfarlandi
d. Two-spotted octopus, Octopus bimaculoides
b: Courtesy Larry S. Roberts; c: © Kenneth W. Fink/Bruce Coleman, Inc.; d: © Ken Lucas/Visuals Unlimited

14. 30.3 The Trochozoa Gastropods (class Gastropoda)
Nudibranchs, conchs, and snails
Foot is flattened ventrally
Move by muscle contractions along the foot
Some are herbivores, others carnivores
Nudibranchs (sea slugs)
Lack shell
Conchs and snails have a shell
Protection
Prevents desiccation in land snails

15. Nudibranchs

16. Conch Shell

17. Gastropod and Cephalopod Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
eye
hermaphroditic
gland
shell
cerebral
ganglion
tentacle
radula
pedal
ganglion
penis
foot

18. Gastropod and Cephalopod Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
growth
line
eyes
spiral
shell
foot
a. Land snail
© Farley Bridges; 18

19. 30.3 The Trochozoa Cephalopods (class Cephalopoda)
Squid, octopus, nautilus
Foot has evolved into funnel or siphon
Powerful beak and radula for feeding
Cephalization is apparent
Octopuses have no shell, squid have reduced shell
Octopuses thought to be among the most intelligent invertebrates

20. Squid

21. Fig. 30.11d fin pen mantle suckers gill ink sac arm anus funnel eye
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig d
fin
pen
mantle
suckers
gill
ink sac
arm
anus
funnel
eye
tentacle

22. © Georgette Douwma/Photo Researchers, Inc.
Fig e
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
fins
eye
tentacles
with
suckers
b. Squid
© Georgette Douwma/Photo Researchers, Inc.

23. Octopus

24. Octopus

25. Giant Squid

26. Swimming Nautilus

27. Gastropod and Cephalopod Anatomy
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
eye
hermaphroditic
gland
shell
cerebral
ganglion
fin
pen
mantle
suckers
gill
tentacle
ink sac
arm
radula
anus
pedal
ganglion
funnel
penis
eye
growth
line
fins
tentacles
with
suckers
eye
eyes
foot
spiral
shell
foot
tentacle
a. Land snail
b. Squid
a: © Farley Bridges; b: © Georgette Douwma/Photo Researchers, Inc. 27

28. 30.3 The Trochozoa Bivalves (class Bivalvia)
Clams, oysters, scallops, mussels
Two-part shells secreted by mantle
Filter-feeders: water enters through incurrent siphon
Visceral mass
Coelom is reduced
Pericardial cavity is the only remains of the coelom
Described as an open circulatory system because blood flows through sinuses in organs
Sexes separate – trochophore larvae in marine clams

29. Clam, Anodonta pericardial cavity umbo anterior aorta heart kidney
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pericardial cavity
umbo
anterior aorta
heart
kidney
posterior ganglion
posterior retractor muscle
digestive gland
stomach
posterior adductor muscle
anterior adductor muscle
posterior aorta
esophagus
shell
anterior ganglion
anus
mouth
excurrent siphon
labial palps
foot ganglion
incurrent siphon
foot
gill
gonad
intestine
mantle

30. Scallop-adductor muscle

31. Oyster bed

32. Oyster

33. Pearls

35. 30.3 The Trochozoa Annelids (phylum Annelida)
Only trochozoan with segmentation and a well-developed coelom
Hydrostatic skeleton
Specialization of digestive tract
Closed circulatory system
Brain with nerve cord connecting ganglia in each segement
Excretory system – nephridia in most segements
Tubule for collecting waste material

36. Polychaetes 30.3 The Trochozoa Have many setae or bristles
Anchor worm or help in locomotion
Used for swimming and respiration
Active predators or sessile forms
Trochophore larva

37. © Heather Angel/Natural Visions;
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
sensory
projections
parapodia
a. Clam worm, Nereis
© Heather Angel/Natural Visions;

38. a: © Heather Angel/Natural Visions; c: © Diane R. Nelson
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
sensory
projections
pharynx
(extended)
sensory
projections
jaw
eyes
parapodia
parapodia
a. Clam worm, Nereis
b. Head region of Nereis
spiraled
tentacles
c. Christmas tree worms,
Spirobranchus
a: © Heather Angel/Natural Visions; c: © Diane R. Nelson

39. 30.3 The Trochozoa Oligocaetes (class Oligochaeta) Includes earthworms
Few setae per segment
Head is not well developed
Gas exchange is across the body wall
Scavengers on dead or living organic matter
Evidence of segmentation in many systems
Hemraphroditic
Clitellum
No larval stage

40. a. pharynx brain mouth esophagus coelom hearts (5 pairs) crop
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
pharynx
brain
mouth
esophagus
coelom
hearts (5 pairs)
crop
seminal vesicle
dorsal blood vessel
nephridium
ventral blood vessel
ventral nerve cord
anus
clitellum a.

41. coelomic lining longitudinal muscles
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
dorsal blood vessel
coelomic
lining
longitudinal
muscles
muscular wall
of intestine
circular muscles
nephridium
typhlosole
setae
coelom
ventral
blood vessel
cuticle
excretory
pore
ventral nerve cord
subneural blood vessel b.

42. © Roger K. Burnard/Biological Photo Service
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
clitellum
anterior end
clitellum
anterior end c.
© Roger K. Burnard/Biological Photo Service

43. 30.3 The Trochozoa Leeches (class Hirudinea) Most live in freshwater
No setae
2 suckers – one around mouth, large posterior one
Some free-living but most are fluid feeders
Hirudin prevents blood coagulation

44. Leeches

45. Medicinal Leeches