BIO2231 Lecture Notes - Lecture 5: Strobilation, Commensalism, Schistosomiasis
30 May 2018
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Phylum Platyhelminthe: Flatworms, flukes, tapeworms
• Bilateral, tissue-organ, digestive cavity (no anus), dorsoventrally flattened, cephalized
• Triploblastic (ectoderm-epidermis, mesoderm-most tissues and organs, endoderm-gut)
• Acoelomate (no body cavity, fluid filled space, between the digestive cavity and the epidermis
• Organs are embedded in a mesodermally derived parenchyma (fills space between muscles and
visceral organs, noncontractile portions of muscle cells)
• Some have digestive system (incomplete): mouth -> pharynx -> branching gut (parasites have
lost this) Flatworms have no internal transport system, so the branched intestine often extends
throughout much of the body to deliver nutrients to all tissues
• Intestine: one opening, blind ending
• Free living (Planaria); ciliated epidermis, rhabdites= epidermal cells that produce mcuous
• Parasitic=Neodermata (tapeworms and flukes); non ciliated syncitical (cells have fused to
become one big cell with multiple nuclei) tegument (skin) provides resistance to immune
system/gut enzymes
• Muscular system: Circular and longitudinal muscle fibres (mesodermal)
• Excretory: flame cells/protonephridia (create current of fluid into tube to get rid of excess fluid
• Nervous system: ladder shaped, longitudinal nerve cord, cerebral ganglia (brain)
• Sensory organs: eye spots, statocysts
Class Turbellaria
-Flatworms
-Almost all are free living
-mostly marine
-possess digestive system
-ciliated epidermis
-unsegmented
-live on prey or dead animals
Planaria
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Document Summary
Contains rod-shaped rhabdites, which swell and form a protective mucous sheath around the body when discharged in water. Nitrogen from protein metabolsim is largely removed by diffusion through the body wall. Size of the animal tends to be related to both the structure of the intestinal sac and the degree of body flattening. Layer of glycoproteins to avoid detection by host. 2 suckers (no hooks), oral, encircling mouth for feeding and ventral (acetabulum) for attachment. Lifecycle; intermediate (can have 2-4, usually molluscs, snails) then definitive host (vertebrate) Body in 2 parts; anterior scolex for attachment (hooks and suckers), posterior series of proglottids (sex organs and eggs) Strobila consists of proglottids which contains complete set of male and female reproductive organs (new ones are formed in neck region) Egg (shell embryo) -> miracidium (penetrates tissue of snail, free swimming, ciliated larva) ->
