Transcript Flatworms are placed in 3 classes

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Flatworms are placed in 3 classes
Class Turbellaria: Turbellarians are mostly free-living worms that
range in length from 5mm-50cm.
Ex. Dugesia
Class Cestoda: The cestodes, or tapeworms, have long flat bodies made up of
many reproductive units and have no digestive system.
Ex. Taenia
Class Trematoda: Trematodes are all parasitic flukes, and as adults
they are almost all found as internal parasites of vertebrates
Ex. Schistosoma, Clonorchis
Characteristics
•
Symmetry: Bilateral
•
Cleavage: None
•
Coelomate/ Acoelomate: Acoelomate because there is no cavity. It has a layer of mesenchyme instead of a
coelom
•
Integument: 3 layered body with layers closely packed to each other
Skeletal System
• Platyhelminthes have a hydrostatic skeleton
•
Platyhelminthes rely on their hydrostatic system for support. The combination of the mesenchyme and the
flexibility of the body wall makes it an adequate means of support. The body wall is a ciliated epidermis
and does not possess a cuticle. Since there is no cuticle, the flatworms use their intracellular fiber and basal
lamina to support the wall. This makes the wall more flexible than a body wall surrounded by a cuticle.
Muscular System
• Small aquatic tubellarians move with cilia
• Larger flatworms use muscular contractions for creeping and other types of
locomotion
•
Planarian dual glands and cilia
Digestive System
Class
Turbellanians
Feeding
Feed
on
invertebrates
Digestion
small 




Mouth is used for both ingestion &
excretion.
Mouth leads to pharynx and is
followed by the gut
Some have intestines
Digestion begins extracellularly
Phagocytosis
Cestodes
Feed on host (intestine 
of a vertebrate animal) 


Possess no gut or simple gut
No mouth or digestive tract
Absorb food from environment
Digestion is intracellular
Trematodes
Feed on host tissue 
through pharynx

Contain mouth and simple gut
Digestion is extracellular and then
intracellular
Feeding and Digestion
•
•
(Above) Taenia solium
(Left) The mouth of Taenia
pisiformes
•
(Right) Cestoda - Taenia pisiformis Scolex, and interior suckers of a
tapeworm.
Circulatory System
• Flatworms lack a specialized circulatory system, thus they use….
Respiration
• Flatworms lack any specialized structure for gas exchange, so it occurs by…..
Have
you
guessed
it yet??
Did you
Can
guess
youDiffusion??
guess??
Excretory System
•
•
•
•
The Excretory System is a network of fine
tubules
Side branches consist of flame cells which move
water towards exit pores
This system regulates water balance
Metabolic waste leaves by diffusion
Turbellaria - Flame cell - protonephridia.
Nervous/ Sensory System
Turbellaria-The
Nervous system of
a Dugesia.
• Generally Diffuse
• Longitudinal Nerve Cords
Turbellaria - Bdelloura candida - Detail of the anterior end showing
the brain, eyespots and the longitudinal nerve cords. Anterior
branches of the intestine are also visible.
Reproductive System
• Simple & Complex
• Asexual (Hermaphrodites)
Structure of Amphilinidea (above)
Larvae (left)
Reproductive System
•
From Left to Right: A) Cestoda - Taenia pisiformis - Immature proglottid showing the developing reporductive
structures. B) Cestoda - Taenia pisiformis - Mature proglittid showing the main reproductive structures including
ovary, vitelline gland, testes,and ducts. C) Cestoda - Taenia pisiformis - Gravid (ripe) proglottid of a tapeworm
showing the genital pore and the eggs contained in the proglottid.