Platyhelminthes

What type of symmetry do Platyhelminthes exhibit?

Bilateral — primitive form

What type of body complexity do Platy have?

Triploblastic acoelomates

What germ layers are included in triploblastic individuals

• Mesoderm

• Endoderm

• Ectoderm

What simple functions do Platy lack?

Circulatory and respiratory organs

What are two unique organs at the complexity of Platy?

Blind gut and brain

Define blind gut

The mouth and anus are the same

Are Platy segmented or unsegmented?

Can be either

Where do Platyhelminthes live?

Some free living, some parasitic

What are the three classes of Platyhelminthes and what organisms are found in them?

• Turbellaria:

  • All free living

  • Most are marine, but some are freshwater and terrestrial

  • Planaria

• Tremetoda:

  • Parasitic flukes

• Cestoda:

  • Tape worms

What individuals does Turbellaria include?

All sub-groups of Platyhelminthes that are not parasitic

• Some living in fresh water, some in marine habitats

• Most are predators

How many species in Turbellaria and how large are they

• About 4,500 species

• Most are small — around 1mm

• Some get up to 25in — in which case they become ribbon shaped

How does Turbellaria reproduce?

All reproduce sexually

• Most are hermaphroditic

• Larvae look like ciliated planula

What are neoblast cells and what are they found in?

They allow for regeneration

• Turbellaria

How does Turbellaria respire?

Diffuse oxygen throughout their body

What type of digestive organ does Turbellaria have?

Blind pockets with branches — help in digestion and transfer of nutrients throughout the body

Explain excretion in Turbellaria

Flame cells form on each side of the stomach

• Get rid of metabolic waste

• Protonephrida - collection of flame cells

How does Turbellaria balance internal water levels?

Small pores on the epidermis open to allow water in and out

How do Turbellaria “see”/sense?

Use eye spots for light, which contain statocysts for balance

Explain transportation in Turbellaria

Cilia on bottom of the organism

What type of muscles do Turbellaria have and what do they do?

• Circular: outermost muscles which elongate body

• Longitudinal: right underneath circular muscles - shorten body

• Diagonal: have more specific, complex responses - can flatten body

Explain Turbellarian reproduction?

Most are hermaphroditic and produce few large eggs

• Separate sexes are rare

• Have many elaborate reproductive methods: penis fencing

Explain penis fencing

• Turbellaria use two-pronged penis to try to stab each other

• Anywhere on the body that is stabbed, sperm is deposited

• It is not an advantage to be pregnant (due to energy expenditure), so they must fight for fatherhood.

Name the 5 main orders of Turbellaria and what types of organisms these orders encompass:

• Acoela

  • No gut cavity —> have cells with digestive capabilities

• Rhabdocoela

  • Simple tubular gut

• Allocoela

  • gut has one main branch with more complex pharynx

• Trocladia

  • Triclad gut

  • many species, including Planaria — successful

• Polycladia

  • Branched gut

  • most marine

  • Also successful

Name the class and the letters of the body plan

Turbellaria - Planaria

A. Eye spots

B. Gastrovascular cavity

C. Ventral nerve cord

D. Mouth

E. Pharynx

F. Protonephridium

G. Brain

Name the class and label

Turbellaria - Planaria

A. Mesodermal parenchyma

B. Proboscis cavity

C. Proboscis

D. Proboscis dorsal epidermis (with rhadbites)

E. Gut branches

F. Ciliated ventral epidermis

G. Diagonal muscles

H. Inner longitudinal muslces

I. Outer circular muscle

What individuals does Tremetoda include?

Parasitic flukes

• contain oral suckers

• 18,000-24,000 species

What is the body plan for Tremetoda?

Essentially the same as Turbellaria but without cilia

What type of eggs do Tremetoda create?

Large groups of small eggs

What is the main goal for parasitic organisms?

To not be found by the host — remain hidden and reproduce as much as possible

• Usually do not have pathogenic effect on host

What are some parasitic adaptations that Tremetoda and Cestoda have?

• Reduced sense organs - no eye spots

• Reduced locomotion - no cilia

• Reduction/loss of ability to maintain homeostasis

• Elaborate/complex lifecycle - usually with multiple hosts and can sexually and can asexually reproduce at various parts of maturity

• Organs of attachment

• High reproductive capacity

Explain the characteristics of subclass Monogenea

Phylum: Platyhelminthes

Class: Tremetoda

• Ectoparasites: live on outside of the host body

  • Usually hosts on lower vertebrates like fish and amphibians

  • Commonly found on skin, gills, and fins

• Very simple life cycle

  • No intermediate host

  • eggs develop into adult

• Causes fish to be lethargic, gulp for air, and try to scrape parasites off.

Explain Monogenea lifecycle

Phylum: Platyhelminthes

Class: Tremetoda

Subclass: Monogenea

Briefly explain subclass Digenia

Phylum: Platyhelminthes

Class: Tremetoda

• Endoparasites: parasite is inside the host

• Have at least 2 hosts

  • Primary hosts: where it reaches sexual maturity and sexually reproduces

  • Intermediate host: where asexual reproduction occurs

Explain Digenia body plan

• Relatively simple gut

• Complex hermaphroditic genitalia

• Ventral sucker to attach to host

• Male pore with sperm duct

• Female pore with uterus and ovary

Explain the maturation steps that Digenia goes through within an intermediate host

1. Eggs enter intermediate host

2. Eggs hatch into miricidium

3. Miricidium develops into sporocyst

4. Sporocyst asexually reproduces redia

5. Redia develop into cercaria

Name the subclass and label

Phylum: Platyhelminthes, Class: Tremetoda, Subclass: Digenia

A. Mouth

B. Pharynx

C. Gut

D. Female pore

E. Uterus

F. Ovary

G. Yolk duct

H. Seminal receptacle

I. Testes

J. Shell gland

K. Yolk gland

L. Sperm duct

M. Ventral sucker

N. Male pore

O. Oral sucker

P. enelope is Digenia

Describe the life cycle of Clonorchis sinensis

Phylum: Platyhelminthes

Class: Tremetoda

Subclass: Digenia

Describe the characteristics of sheep flukes - Fascicola hepatica

Phylum: Platy

Class: Tremetoda

Subclass: Digenia

Species: Fascicola sp. (hepatica)

• Common definite primary hosts are humans and ruminants

• Encyst on grass tips

• The snail intermediate host can pick up the egg or miracidium

• Wider distribution than Clonorchis

• Adult flukes travel to bile duct and feed on bile

Describe Fascicola hepatica lifecycle

Phylum: Platy

Class: Tremetoda

Subclass: Digenia

Species: Fascicola sp. (hepatica)

Describe the overall characteristics of blood flukes - Schistisoma spp.

Phylum: Platy

Class: Tremetoda

Subclass: Digenia

Species: Schistisoma spp.

• Eggs hatch into miracidium before or during intermediate snail phase

• Cercaria has a forked tail

• Blood flukes only use mammals as primary hosts and only use snails as secondary hosts - no other hosts

• Cercaria penetrate skin of human in or near water and absorb its tail for nutrients

Describe the Schistisoma body plan

Phylum: Platy

Class: Tremetoda

Subclass: Digenia

Species: Schistisoma spp.

Explain the subclasses of Cestoda

Cestoda - tapeworms

• 6,000ish species - all parasitic

• Subclass: Cestodaria

  • Unsegmented

• Subclass: Eucestoda

  • Segmented

Describe basic eucestoda body plan

Phylum: Platy

Class: Cestoda

Subclass: Eucestoda

• Scolex (head)

• Proglottid - segmented individuals with female and male reproductive organs that can produce 50-100 eggs

• No gut - endoparasite of hind gut and just absorbs you

Describe the lifecycle of Taenia

Phylum: Platy

Class: Cestoda

Subclass: Eucestoda

Genus: Taenia (pissiformis) - beef and pork tapeworms

Describe the lifecycle of Echinococcosis

Phylum: Platy

Class: Cestoda

Subclass: Eucestoda

Genus: Echinococcosis - dog tapeworm

What are larval Eucestoda called?

Bladder worms