1. Discuss the current triploblastic acoelomate
body plan.
2. Discuss the concept of the organ/system level
of organization and apply this to the phylums to be studied in this unit.
3. Define bilateral symmetry and cephalization.
4. Compare the enbryo development in cnidarians
and in the higher metazoa, including presence, formation and function of
the mesoderm.
5. Explain what excretion consists of and tell
why excretory systems are necessary in the more complex animal groups.
6. Describe flame cells and their function
in general, and the excretory system of planaria in particular.
7. Briefly describe these advances of the flatworms
over previously studied phyla: symmetry, nervous and sensory systems, mesoderm
formation, muscle systems, excretory systems, digestive systems and reproductive
systems.
8. Explain the terms hermaphroditic, monoecious
and dioecious, and state what animal types in general are hermaphroditic.
9. List features which will be expected in
higher phyla but are not possessed by the flatworms, and tell why these features
are unnecessary in flatworms.
10. State the probable evolutionary relationship
between free-living species and parasitic species in the same group, and
describe three ways in which a species must change as it evolves from a free-living
form to a parasitic way of life.
11. Briefly describe planaria's taxic responses,
nervous system, method of feeding and digestion of food, muscular system
and reproduction.
12. Describe regeneration in planaria.
13. List and briefly describe the ways in which
the Trematoda differ from the Turbellaria.
14. List and discuss specific trends displayed
by organisms that have developed a parasitic mode of existance.
15. Describe the morphology of Clonorchis sinensis
as an example of a digenetic trematode, and outling the life cycle of this
species, including hosts, larval stages, and means of transmission from host
to host.
16. Outline the life cycle of Schistosoma mansoni
and describe the medicinal importance of schistosomiasis.
17. Discuss the critical aspect of reproductive
potential with regard to trematodes and cestodes, describe the numbers game
they must play in order to survive.
18. Diagram the morphology of a tapeworm including
descriptions of the scolex, strobila and proglottids, tell how tapeworms
differ from trematodes.
19. Outline the life cycles of D. latum the
fish tapeworm and T. saginatus the beef tapeworm.
20. Describe the evolutionary significance of
the Phylum Nemertea.
Resources: Text: Animal Diversity, Chapter
8
Internet resources:
http://www.wfu.edu/users/mackgr5/platy.htm
http://www.personal.psu.edu/users/d/m/dmf177/
http://www.mhhe.com/hickmanad4e
Acoelomates body plan pg 147-148
Ectoderm (1)
Mesoderm (3) mesodermal organ
gut- Endoderm (2)
-no coelom, gut only internal cavity
-TRIPLOBLASTIC; three well defined germ
layers (Endo, Ecto, Meso)
-organ/system level of organization
3 ACOELOMATE PHYLA
*Phylum Platyhelminthes (flat worms)
Phylum Nemertea (ribbon worms)
Phylum Gnathostomulida (jaw worms)
BILATERAL SYMMETRY
-appears early in development
-correlated with cephalization (origin of
head region)
-quick responses to stimuli
-concentration of sensory cells
Muscular system} well developed in free living
forms but not parasitic forms
Nervous system} well developed in free living
forms but not parasitic forms
Digestive system} well developed in free living
forms but not parasitic forms
Excretory system} well developed in free living
forms but not parasitic forms
Phylum Platyhelminthes pg 146 summary
pg 147 ~ 13,000 species
-terrestrial, marine, freshwater
-dorso-ventrally flattened
-protonephridium- organ of osmoregulation
-2 of 3 class we will see are entirely parasitic
CLASS TURBELLARIA (free living flatworms)
-bodies flattened dorso-ventrally
-ciliated epidermis w/ RHABDITES
-mouth ventral, leading to gastrovascular
cavity
-anus lacking
-direct development
-Planaria
-Digestive, Excretory, Nervous systems
*very divergent in form
*5 basic types based on gut
NERVOUS SYSTEM
1. Nerve net- sub-epidermal
(nerve plexus)
2. "brain"- 2 or more nerve
cords, longitudinal, connected laterally to form ladder
3. Sensory cells
a. chemoreceptors
b. mechanoreceptors
**a and b are cells w/ sensory cilia
c. eyes- 1 or more pairs; light detection only
d. statocysts- equilibrium, in head region (anterior)
DIGESTION- mouth, pharynx, intestine (not complete), no anus.
-Turbellarian pharynx extends
out of mouth on ventral surface
*intestines simple or branched
*extracellular digestion in
intestine w/ enzymes
*intracellular digestion in intestine uses phagocytosis
OSMOREGULATION/ EXCRETION
-Protonephridia
*branched tubule ("duct") terminating
in a number of blind capillaries that
open to outside pores (nephridiopores)
*flame bulbs w/ beating flagella
(cilia) drive fluid
*osmoregulatory not excretory
*most metabolic wastes diffuse through body wall
*hypotonic situation of fresh water species requires more flame cells than marine
REPRODUCTION
1. Sexual
-widely various
-gonads distinct
-most hermaphroditic (monoecious)
but self-fert uncommon
-usually copulate w/ reciprocal
sperm transfer
-germ cells originate in mesoderm
-fresh water species: 2 kinds of eggs
a. winter- thick, resistant
cocoon, dormant, hatch in spring
b. summer- thin capsule,
hatch quickly
2. Asexual
-transverse fission
-fragmentation (w/ regeneration)
Parasitism
CLASS TREMATODA (flukes)
-(Trematodes- mouth anterior)
CLASS CESTODA- tapeworms
-(Cestodes- no digestive system);
absorb pre-digested food through
tegument, Who needs digestive
system?
-most parasitic species of any phyla
TRENDS IN THE PARASITIC MODE OF EXISTANCE
1. Tremendous reproductive capacities, "egg laying machines"
2. Tegument- syncytial, outer layer
continuous cytoplasm, nucleated but not
divided into cells
3. pepsin and trypsin resistant (won't
be digested)
4. Complex life cycles:
a. one to many hosts (larva --->
adult)
b. often highly host specific (coevolutionary?)
5. specialized entry and feeding structures
6. organs of attachment
7. locomotor structures lost except in
larva
8. sensory structures lost
**not necessarily degenerate! --->
actually highly specialized
Class Monogenea- single birth; flukes;
development direct- single host all
parasitic; most ectoparasites on
fish
Class Trematoda- flukes
-entirely parasitic
-external tegument (cuticle)
-ovoid body w/suckers for attachment
-incomplete digestive system
-complex life cycle w/ larval stages
and intermediate hosts (indirect development)
-adult general body form like
Turbellarians only somewhat larger (ditto for nervous
and excretory)
-syncytial tegument (epidermis,
cilia lost)
-one or more suckers (possible hooks)
-Digenea- endoparasites in circulatory,
respiratory, digestive, urinary,
reproductive. . . . cause more
damage than ectoparasites
-indirect development (usually 2 hosts)
Intermediate host- larval
stages
Definitive host (usually vertebrate)-
adult
-anterior mouth
-enlarged, comples reproductive system
TYPICAL LIFE CYCLE
1. adult trematode sheds eggs ---> human
feces
2. egg hatches into a miracidium (free swimming, ciliated)
3. miracidium eaten or bores into snail (intermediate)
4. when inside host, miracidium becomes sporocyst
5. sporocyst reproduces to form more spores or rediae (asexual)
6. rediae reproduce (asexually)
or
7. rediae produce cercaria
8. cercaria leave snail and penetrate 2nd host
or
encyst on vegetation and become metacercaria
9. when eaten metacercaria develop into adult
**one miracidium can potentially produce
200,000 cercaria in a single
snail (some estimates as high as 300,000!)
**LIFE CYCLE OF Clonorchis sinensis Pg 152
Schistosoma mansoni- blood fluke; 2nd
or 3rd most important disease in world;
Asia, Africa, S. Amer, Mid East; 100-300
million cases per year
**note tremendous reproductive potential
**swimmers itch, bird schistosome
CLASS CESTODA- tapeworms
-entirely parasitic w/ numerous hosts and complex life cycle (indirect development)
-adults parasites in guts of vertebrates
-no digestive tract, no digestive organs
(including mouth)
-thick syncytial tegument similar to
trematodes but serves as sole means of obtaining
nutrition
-exhibit type of segmentation (proglottids)
-very long
-most highly specialized
-microtriches- increase surface area
-monoecious, cross fertilize
-strobila main body
-proglottids newest behind scolex (head w/ suckers and or hooks)
-mature proglottid (gravid) are egg sacs
-life cycles Taeniarhynchus saginatus Pg 156
Taenia solium- pork tapeworm
Diphyllobothrium latum- fish tapeworm
*as a general rule, adult tapeworms do
little harm to hosts
Phylum Nemertea pg 156
-formerly Rhynchocoela (beak) referred to
proboscis
-mostly marine
-bilateral, ciliated epidermis
-flame cells in excretory system
**digestive tract complete (ending
in an anus)
no more regurgitation
-carnivouous
-Proboscis
**true circulatory system (some w/ hemoglobin)
**most are dioecious