Flatworms  Phylum: Platyhelminthes 3 Germ layers Bilateral symmetry Acoelomates: No body cavity  Results in thin, flat bodies  Low surface area:volume ratio Gastrovascular Cavity  Nutrients/Waste enter/exit same location Divided into three classes

Turbellaria  Majority are marine species  Often called planarians  Aquatic scavengers Very simple digestive system Free living, so they need to breakdown their own nutrients  Few live in freshwater Must excrete excess H2O Uses excretory tubule system shown in 36-2

Trematoda  Called Flukes  Mainly parasitic Attach to the host by a sucker Draws body fluid of host into the fluke Tegument  Outer portion of the fluke  Protects against the host’s immune/defense stystem

Fluke Reproduction (36-4)  Complex life cycle Different host at different points in life cycle Primary Host  Host that the adult lives in  Consumes nutrients  Reproduces Intermediate Host  Larval stage of development  Larva get nourishment  Used to get back to the primary Host

Cestoda  Tapeworms  Intestinal parasites Tegument similar to flukes Scolex used to attach to the host Body segments called proglottids  Grows by adding segments  Some may have over 2000 (over 30 ft) Completely lack digestive organs  Absorb directly from host

Cestoda Reproduction  Complex life cycle similar to flukes  Proglottid contains eggs Eggs fertilized by other segment on same worm, or different worm in same host  Proglottid breaks off Carries eggs away in feces  Vegitation contaminated by feces Consumed by herbivore Eggs develop into larva in intermediate host Get to muscle and form cyst  Primary host consumes animal muscle

Phylum: Nematoda  Roundworms Long,slender, tapered at anterior and posterior ends Pseudocoelomates Complete digestive tract  2 openings Covered by a cuticle:used for protection Free living and parasitic

Ascaris  Intestinal parasite Pig, human, horse May block intestinal tract  Enter body through contanimated food Eggs carried out in feces  Egg  Larva in intestine  Larva  Bloodstream  Bloodstream  Lungs/throat  Lungs/Throat  Outside body(cough), intestine(swallowed)

Hookworm  Intestinal parasite  Remove blood Can cause anemia  Eggs released through feces  Eggs develop into larvae in soil  Larvae burrow into foot  Get into bloodstream Follow similar path of ascaris

Trichinella  Embed in intestinal walls  Larvae enter bloodstream, go to muscle, form cyst  Consumed in undercooked meat Mainly pork  ALWAYS WELL DONE!!!  Causes trichinosis Muscle pain/stiffness If in heart = death

Pinworm  Most common in US (16% adult, 30%children) Do not cause major illness Intestinal Eggs deposited outside anus Eggs picked up, moved to other locations Ingested eggs end up back in intestines

Filarial Worms  Tropical Parasites  Some live in lymphatic system  Transferred by mosquitoes Mosquito is intermediate host  Where the larvae develops Transfer to new host  Can completely block lymphatic vessels Causes elephantiasis  Also what causes heartworm in dogs