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Phylum Phylum PlatyPlatyhelmintheshelminthes
The “flat” “worms”The “flat” “worms”
www.onacd.ca
4 Classes of Phylum Platyhelminthes4 Classes of Phylum Platyhelminthes
TREMATODATREMATODA – flukes CESTODACESTODA – tapeworms
MONOGENEAMONOGENEA – small, parasitic flatworms
TURBELLARIATURBELLARIA - small, free-living flatworms
Identifying Characteristics of the Identifying Characteristics of the Phylum PlatyhelminthesPhylum Platyhelminthes
Acoelomate Exhibit bilateral symmetry Have a bilateral nervous system with cephalization
at the head end. Some species exhibit eyespots sensitive to light
Possess a Gastrovascular Cavity (GVC) and primitive organ systems for digestion and excretion
Do not have a circulatory or respiratory system but do take in O2 through their body surface (integumentary exchange)
Hermaphroditic : can reproduce sexually (do not self fertilize) or asexually by regeneration
Are motile and utilize an undulation form of motion Found in marine, freshwater and damp terrestrial
habitats
Free-living FlatwormsFree-living FlatwormsPlanaria : Planaria : Dugesia tigrinaDugesia tigrina
Freshwater, free-living flatworm Moves by beating cilia and gliding
on a film of mucus 3-12mm in size Have a single opening to their
stomachs in the middle of their bodies
Possesses 2 eyespots (ocelli) that are sensitive to light
Carnivorous (eat daphnia and midges)
Common to most parts of the world
Reproduce by asexual reproduction and capable of regeneration (see next slide)
Planaria RegenerationPlanaria Regeneration
Planarians will spontaneously detach the tail end of their bodies and each half will regenerate into a full size flatworm
Planarians can be cut either transversally (shown above) or dorsally and most will regenerate into a full size worm
Super Cool Fact: the smallest piece of planarian to ever regenerate in a lab into a new planarian was 1/279th of a planarian! That’s approximately 10,000 cells!
Parasitic FlatwormsParasitic FlatwormsThe pork tapeworm – The pork tapeworm – Taenia soliumTaenia solium
Infects pigs and humans Lives in the intestine of its host
and passes eggs through the feces Highly adapted to constant
internal environments Lacks sensory organs,
coordination for mobility and a digestive system (more room for reproductive structures!)
Have a modified epidermis “tegument” which protects against the digestive enzymes and the immune systems of the host
Can reach 7m in length in humans! Are flat and long which maximizes
absorption of nutrients from the host
The tapeworm “up close and personal….”The tapeworm “up close and personal….” The head end has a
scolex with four suckers (two seen here) that help it attach to the intestine of its host
The body is separated into sections called “proglottids” that house highly developed reproductive systems (darkened areas) capable of producing hundreds of thousands of eggs and sperm
Life cycle of the Pork TapewormLife cycle of the Pork Tapeworm
Super cool Flatworm FactSuper cool Flatworm Fact• the largest tapeworm ever reported the largest tapeworm ever reported
was in a sperm whale and was 30 was in a sperm whale and was 30 meters in length!meters in length!
Tapeworm Scolex