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Platyhelminthes:
Flatworms
Phylum Platyhelminthes• Phylum Platyhelminthes - Flatworms• Soft, unsegmented, flattened worms that have tissues and internal
organ systems• Have three embryonic germ layers• Simplest animals with bilateral symmetry• Exhibit cephalization• More developed organ systems than Poriferans and Cnidarians• Acoelomates – “without a coelom” – a coelom is a fluid-filled body
cavity that is lined with mesoderm
Anatomy of a FlatwormFreshwater flatworms have simple ganglia and nerve cords that run the length of the body. The excretory system consists of a network of tubules connected to flame cells that remove excess water and cell wastes.
Most flatworms are hermaphrodites, having male reproductive organs (testes) and female reproductive organs (ovaries) in the same organism.
Flatworms use a pharynx to suck food into the gastrovascular cavity. Digested food diffuses from the cavity into other cells of the body. Eyespots in somespecies detect light.
Eyespot
Head
Gastrovascularcavity
Ganglia
Nervecords
Excretorysystem
Mouth Pharynx
Ovary
Testes
Excretorytubule
Flame cell
Feeding in Flatworms
• Can be carnivores or scavengers
• Gastrovascular cavity with one opening at the end of a pharynx
• Digested food diffuses to other body tissues
Respiration, Circulation, and Excretion in Flatworms
• No circulatory system or respiratory organs – rely on diffusion to transport nutrients and waste
• Expel undigested material through pharynx
• Flame cells filter and remove excess water and wastes from body
Response in Flatworms
• Nervous system much more developed than Sponges or Cnidarians
• Definite head
• Simple ganglia control nervous system
• Two nerve cords run from ganglia along both sides of body
• Ocelli, or eyespot, detects changes in the amount of light in their environment
Movement in Flatworms
• Cilia on epidermal cells
• Muscle cells allow to twist and turn to be able to react rapidly
Reproduction in Flatworms
• Sexual – hermaphrodites – two worms join as a pair and deliver sperm to each other
• Asexual – fission – splits in two
Penis Fencing in Flatworms
Groups of Flatworms
• 3 major classes of flatworms– Class Turbellaria– Class Trematoda– Class Cestoda
Class Turbellaria
• Free-living flatworms found in marine or freshwater
• Bottom dwellers
• Planarians – 1/2 cm to 6 m long
Examples of Class Turbellaria
Parasitic Flatworms
• Feed on blood, tissue, or cells; some just absorb nutrients through their “skin”
• Examples: Tapeworms, Flukes
• Very complicated sexual reproductive life cycles
Class Trematoda – Flukes
• Parasitic and infect internal organs of host
• Blood flukes Schistosoma mansoni
• Humans – primary host – burrow through exposed skin
• Many more eggs than free-living flatworms
• Eggs pass out with feces of host
• Tropical areas – Southeast Asia, Africa
Examples of Class Trematoda
Class Cestoda – Tapeworms
• Long, flat parasitic worms• Head of an adult called a scolex – used to attach to
intestinal wall where it absorbs nutrients• 18m long, host may lose weight and become weak• Behind scolex is a narrow neck region that produces
proglottids that break off the tail and rupture in intestine or feces and release embryos
• Eggs consumed by intermediate host• Larvae form cysts in muscle tissue• Tissue then consumed by humans
Life Cycle of Tapeworm
Examples of Class Cestoda
Nematoda:
Roundworms
Phylum Nematoda• Phylum Nematoda - Roundworms• Slender, unsegmented worms• Pseudocoelom – body cavity only partially lined with
mesoderm• Two openings, mouth and anus, in digestive system –
“tube-within-a-tube” – food moves only in ONE direction• Microscopic in size to 1m long• Can be decomposers or dangerous parasites• Might be the most common multicellular animal• Most are free-living, found everywhere
Feeding in Roundworms
• Mainly carnivores, some eat algae or decaying organic matter
Respiration, Circulation, and Excretion in Roundworms
• Exchange gases and excrete metabolic wastes through diffusion
• No internal transport system
Response in Roundworms
• Simple nerve network, ganglia
Movement in Roundworms
• Muscles and fluid = hydrostatic skeleton
Reproduction in Roundworms
• Sexual – internal fertilization
• Ascarid worms – complex life cycles involving two or three different hosts or several organs within a single host
• Stomach – lung – throat – intestine - feces
Examples of Nematodes
Roundworms and Human Disease
• Hookworms – similar to Ascaris lifecycle, except they enter through the skin
• Filarial Worms – elephantiasis (swelling of body) – transmitted by mosquitoes
ORGANISM
Trichinella
Filiarial worms
Ascaris
Hookworms
ORGANISM
Trichinella
Filiarial worms
Ascaris
Hookworms
DISEASE
Trichinosis
Elephantiasis
Ascaris infection/infestation
Hookworm infection/infestation
DISEASE
Trichinosis
Elephantiasis
Ascaris infection/infestation
Hookworm infection/infestation
ROUTE OF INFECTION
Eating undercooked meat containing larval cysts
Bite of insect carrying filarial worms
Eating unwashedfood contaminatedwith Ascaris
Bare skin in contact with contaminated soil
ROUTE OF INFECTION
Eating undercooked meat containing larval cysts
Bite of insect carrying filarial worms
Eating unwashedfood contaminatedwith Ascaris
Bare skin in contact with contaminated soil
DESCRIPTION
Larvae burrow into tissues of host, causing pain
Worms block passage of fluids within lymph vessels, causing tissues to swell
Worms in intestine block normal passage of food and absorption of nutrients
Worms attach to intestinal wall and suck blood, causing weakness and poor growth
DESCRIPTION
Larvae burrow into tissues of host, causing pain
Worms block passage of fluids within lymph vessels, causing tissues to swell
Worms in intestine block normal passage of food and absorption of nutrients
Worms attach to intestinal wall and suck blood, causing weakness and poor growth
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