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 5. Uncooked meat in consumed 1. eggs released 3. eggs eaten 4. larvae migrate to muscle & form cysts 2. eggs on grass

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