Phylum Phylum PlatyPlatyhelmintheshelminthes

The “flat” “worms”The “flat” “worms”

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4 Classes of Phylum Platyhelminthes4 Classes of Phylum Platyhelminthes

TREMATODA – flukes CESTODA – tapeworms

MONOGENEA – small, parasitic flatworms

TURBELLARIA - 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 two 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