1. Acoelomate Bilateral Animals PLATYHELMINTHES
Chapter 14
Acoelomate Bilateral Animals
PLATYHELMINTHES

2. Overall Characteristics
Acoeolomate
Only one internal space
Bilateral Symmetry
due to cephalization
Triploblastic
Three germ layers (formed during embryonic development)
Middle mesodermal layer: parenchyma

3. Platyhelminthes: the classes
1. Turbellaria
free living flatworms
2. Monogenea
Most are ectoparasites
3. Trematoda
flukes
All are endoparasites
4. Cestoda
tapeworms

4. I. Form and Function Most have Ciliated epidermis Epidermis (Tegument)
syncytial (multinucleated)
Basement layer
separating epidermal from organ layers
contains rhabdites
Produce mucous

5. Muscle fibers below basement layer
Dual-gland adhesive organs (turbellarians)
Viscid gland = stick
Releasing gland = release
1 Anchor cell

6. A. Nutrition and Digestion
Mouth, pharynx & intestine (except cestodes)
gastrovascular cavity
branching

7. Mostly free-living & carnivorous detect prey by chemoreception
Like smelling them!
Extracellular digestion
enzymes
Intracellular digestion
phagocytosis

8. B. Excretion & Osmoregulation
Protonephridia
Osmotic balance
Some ammonia excretion (nitrogenous waste)…, but most by diffusion through body wall
Flatworm kidney
Made of flame cells
Function: osmoregulation

9. C. Nervous System Brain Longitudinal Nerve cords Anterior Ganglia
Bundle of neurons
Longitudinal Nerve cords
Sensory: collect info from environment
Motor: action
Association: link

10. D. Sense Organs 5 sense organs Mechanoreceptors - tactile (touch)
Chemoreception - taste / smell, mates?
Rheoceptors (H2O flow)
Statocysts - balance
Ocelli - simple vision

11. Turbellaria
Polyphiletic (p. 302)
Simple life cycles
.5 to 50cm iin length
Midventral mouth or proboscis (planaria)
Not at anterior (head) end
Muscular waves & or ciliary locomotion
Gut varies from none to highly branched (correlates with size)
Order Acoela (primative marine flatworms) only mouth, no gastrovascular cavity!
Amazing regenerative abilities- planaria developmental studies

12. E. Reproduction Turbellarians (e.g.. Planaria)
Endolecithal (yolk) and ectolecithal (no yolk)
Embryos emerge as juveniles (similar to adults)
Fission
Monoecious
= hermaphroditic
Protostomes with spiral determinate cleavage
cross fertilization
Genital pore
= vagina
Oviduct, eva
Cirrus
= penis
Testes, vas deferens

13. Reproductive System

14. III. Class Trematoda (flukes)
Parasitic
Vertebrate host and invertebrate Intermediate host
Leaf-like
Suckers (two) & or hooks
Well developed
alimentary canal
Nervous system (non-sensory)
Excretory system
Reproductive system
A. Subclass Digenea
Mollusk intermediate
Human definitive host
Pass via excreta to H2O
Infect many body systems
Digestive
Respiratory
Urinary
reproductive
Circulatory system

15. B. Liver Fluke 1. All trematodes are parasitic flukes.
2. Most adults are endoparasites of vertebrates.
Most sporocysts are endoparasites of invertebrates.
3. They resemble some Turbellaria but the tegument lacks cilia in adults.
4. Adaptations for parasitism include:
a. penetration glands,
b. glands to produce cyst material,
c. hooks and suckers for adhesion, and
d. increased reproductive capacity!!!
5. Sense organs are poorly developed.
250,000

16. Fluke life cycle
Clonarchis (liver fluke)
More
Egg (Shelled miracidium)
Miracidium (free swimming larva) penetrates first invertebrate host
Sporocyst forms in host (asexual reproduction)
Rediae from sporocyst which also reproduce asexually to create..
Cercariae which emerge from the intermediate host to become..
Metacercariae which infect another intermediate or final vertebrate host and mature, usually after ingestion
Eg. Chinese liver fluke (monoecious)
Multiplication
1 miracidium to 250,000 cercariae!!!

17. Be careful what you drink, eat, & where you wade!
C. Schistosoma
(blood flukes)
Sexual dimorphism (dioecious)
Male larger than female
Snail
Human (penetrates skin)
million people infected globally
Multiple organ infection
Sometimes fatal
No rediae intermediate
Cirrhosis of the liver (eggs)
Image
Lung Flukes
Snails
Crabs and crayfish
Vertebrates (humans)
Leucochloridium paradoxum
snails and birds
sporocyst
Be careful what you drink, eat, & where you wade!

18. V. Class Cestoda Tapeworm Form Life Cycle Taenia saginatus (beef)
Taenia solium (pork)
Form
Gutless wonders!
Microtriches (tegument)
Scolex
Germinative zone
Proglottids (Strobila chain)
Life Cycle
Monoecious
Self fertilization (or not)
Gravid proglottid
Shelled larvae
Consumed by intermediate
Muscle cysts
Bladder cysts (invaginated cysticercus)
Hydatid cyst (dog tapeworm)
Uncooked meat
Definitive host consumes intermediate host
Cysticercosis (ingestion of eggs or proglottids)

19. Class Cestoda
1. Tapeworms have a unique flattened and segmented shape compared to other flatworms.
2. Each trailing segment is a proglottid containing a set of reproductive organs.
3. The entire surface of cestodes is covered with projections similar to microvilli seen in the vertebrate small intestine; these microtriches increase the surface area for food absorption.
4. Nearly all are monoecious.
5. They lack sensory organs except for modified cilia. (Fig )
6. The scolex is a holdfast head portion with suckers and hooks.