Post on 18-Jan-2016
Flatworms
Honors Biology- Spring 2009Honors Biology- Spring 2009
Phylum Platyhelminthes
Soft, flattened bodies
Bilateral symmetry with cephalization
Form and Function
3 germ layers, but acoelomate Without a coelem
Fluid filled body cavity lined with mesoderm
Digestive cavity (lined with endoderm) is only body cavity
Some free-living, some parasitic Specialized tissues and organs
Feeding
Gastrovascular cavity, single opening (serves as both mouth and anus)
Pharynx- extension from mouth that helps pump food into g.v. cavity
Digestion via diffusion
Respiration, Circulation, Excretion
Because bodies are flat and thin…
Respiration: O2 via diffusion
Circulation: nutrients transported throughout cells via diffusion
Excretion: CO2 and other wastes diffuse out
Response
Ganglia- group of nerve cells that control nervous system--- not complex enough to be a brain
Eyespot- used to detect light intensity in environment
Effective at gathering info. about surroundings
Movement
Cilia on epidermal cells
Muscle cells controlled by nervous system
Reproduction
Sexually Hermaphrodites-
contain both sex organs
Pair joins and exchange sperm
Each will lay fertilized eggs
Asexually Fission- splits in 2
and each half grows
Three Classes of Flatworms1. Class Turbellaria
§ Free-living§ Aquatic (fresh or marine)§ Ex. Planarians
2. Class Trematoda
“Flukes” Parasitic
Infects internal organs
Ex.- Schistosoma mansoni (“Blood Fluke”) Burrows thru exposed skin Carried to blood vessels of small
intestine Mature, reproduce, embryos passed
through feces
Causes Schistosomiasis- Eggs clog
blood vessels and cause tissue decay
3. Cestoda
“Tapeworms” Parasitic Live in intestines
of animals, including humans
No digestive system Simply absorb
host’s food
Head is called a scolex- suckers/hooks to attach to intestinal wall
Segments of body are called proglottids Can break off to
form new tapeworms