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Phylum: Platyhelminthes. “flatworms” Examples: tapeworms, flukes, planarians . Traits . Flattened, worm-like body. Traits . Bilateral symmetry. Traits . Cephalized – have a distinct head end with a concentration of sensory nerves and brain. Traits . Ladder-like nervous system. Traits . - PowerPoint PPT Presentation
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Phylum: Platyhelminthes
• “flatworms”
• Examples: tapeworms, flukes, planarians
Traits
• Flattened, worm-like body
Traits
• Bilateral symmetry
Traits
• Cephalized – have a distinct head end with a concentration of sensory nerves and brain
Traits
• Ladder-like nervous system
Traits
• 3 cell layers
Traits
• Blind sac digestive system
Types
• Planarians – free living flatworms• Tapeworms – segmented parasitic flatworms• Flukes – non segmented parasitic flatworms
Planarian structure
• Ectoderm (epidermis) – outside layer of cells
• Endoderm – inside layer of cells
• Mesoderm – the middle layer of cells
Mesoderm
• Advantage – allows for the development of complex internal organs
• Disadvantage – since not every cell is in contact with the water, getting oxygen and getting rid of wastes is a problem
Planarian structure
• Eyespot – detects light but can’t see shapes and images
Planarian structure
• Flame cells – excretory structures, collect nitrogenous wastes and force them out of the body through a series of tubes
Planarian structure
• Digestive system – blind sac, branches a lot so no cell is very far from food
Movement
• Can glide on ventral cilia or use muscles to swim
Reproduction
• Asexual – by regeneration or binary fission
Binary Fission
Reproduction
• Sexual – hermaphrodites, must exchange sperm (mate) with another worm
Tapeworms
• Segmented parasitic flatworms
Advantages of parasitism
• Food is readily available• don’t waste energy through movement• protected from the environment
Disadvantages of parasitism
• If the host dies, they die• Must get offspring to another host• Must produce a lot of offspring
Tapeworm Structure
• Scolex – head of a tapeworm
Tapeworm Structure
• Hooks and suckers – attach the tapeworm to the host’s intestinal wall
Tapeworm Structure
• Neck – pinches off proglottids
Tapeworm Structure
• Proglottids – reproductive segments of a tapeworm
Tapeworm Structure
• Cuticle – non cellular outside layer that keeps them from being digested from the host’s enzymes
Tapeworm Infestations
Symptoms
• Weight loss and fatigue• Final diagnosis is from a stool sample
Cure
• Easy• Since they live in the intestines, the medicine
goes directly to them, then they are eliminated with the feces
Life Cycle
• Adults live in the human intestines, mate, eggs leave with the feces
• A pig ingests food or water contaminated with the eggs
• Eventually lodge and form cysts in pig’s muscle• A human eats poorly cooked pork and it starts
all over again
BEEF TAPEWORM LIFE CYCLE
1. eggs released
2. eggs on grass
3. eggs eaten
4. larvae migrate to muscle & form cysts
5. Uncooked meat in consumed
Cysts in contaminated pork
Prevention
• Cook meat well• Good sewage systems
Flukes
• Non segmented parasitic flatworms
Flukes
• Endoparasites – live inside the body
Cure?
• Very difficult• Since they live in liver, medicine doesn’t go
directly to them• If you do kill them, the body can’t eliminate
them easily
Sheep liver fluke
• Live in a sheep’s liver• Can clog the bile duct and possibly kill the
sheep
Alternation of hosts
• Need at least 2 separate hosts to complete its life cycle
Life cycle
• Adults live inside the sheep’s liver, mate, eggs leave with feces
• Hatch into larvae which enter snails, reproduce asexually
• Leave snails and form cysts on grass which is eaten by the sheep and start over
Prevention
• Spray and kill the snails
Chinese liver fluke
• Infest the liver of humans
Life cycle
• Adults live in the human liver, mate, eggs leave with feces which is used to fertilize fields
• Flood irrigation washes them into rivers, hatch into larvae which enter snails, reproduce asexually
• Leave snails and enter fish which are eaten raw by humans and start over
Prevention
• Cook the fish• Use other fertilizers• Other irrigation methods