platyhelminthes - sniemeyer12.files.wordpress.com · 03/06/2011 · 4/6/2011 1 platyhelminthes...
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Platyhelminthes
Simplest animals to have bilateral symmetry (milestone)
Soft-bodied, flat worms
Two Forms
Free Living
Parasitic
Platyhelminthes phylum is divided into three classes
Turbellaria
Trematoda
Cestoda
PlatyhelminthesClass: Tubellaria
Example: Planaria
Free Living“Cross-Eyed” wormsCan be up to 20 inches in lengthBottom Dwellers- feed on smaller animals and dead animals
Vary greatly in color, form, and size
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Platyhelminthes: Planarian
PlatyhelminthesClass: Trematoda
Example: Fluke
Resides in multiple hostsLives in digestive organs, liver, or blood of their primary hostUp to ½ inch in lengthCauses Schisteosomiasis
Eggs clog blood vessels, cause swelling and tissue decayCommon in undeveloped tropical areas that lack proper sanitary methods
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PlatyhelminthesClass: Cestoda
Example: Tapeworm
Live in the intestine of their primary hostSize range: very small to 15 meters in lengthCovered by a cuticle used for protection so that they don’t get digested in the intestine
Platyhelminthes: Tapeworm
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Platyhelminthes: Body Form & Skeleton
Bilateral SymmetryHydrostatic SkeletonAceolom
Platyhelminthes: Muscles & Locomotion
Free-Living Parasitic
Two methods1. Cilia on outside of body
- used for gliding through water
2. Muscle cells controlled by nervous system
- twist and turn motions
Adult form doesn’t move once it is attached to its primary host
Larva are able to swim in the water to find primary or intermediate host
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Platyhelminthes: Digestion
Free-Living Parasitic
Feed off of tiny aquatic animalsGastrovascular CavityPharynx -> Mouth -> Gut
Feed on blood, tissue fluidsGet nutrients from host’s digested food in intestine or other organsFluke: Pharynx Intestinal SacsTapeworm: doesn’t have a mouth, diffuses nutrients from host
Platyhelminthes: Respiration, Circulation, Excretion
Flat, thin bodies so they use diffusion to transport materialsno organs for respiration or circulation
Do have organs to remove liquid wasteFlame Cells – remove liquid waste from worm
Groups together to form a network of tubes and expel waste through pores in the body (nephridia)
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Platyhelminthes: Nervous System
Free-Living Parasitic
CephalizationGanglia
Two long nerve cords come off of the ganglia
Connected with lateral nerve cords (ladder-like structure)
Eyespots
Interact little with external environment so they have a very simple nervous system
Platyhelminthes: Reproduction - Free-Living
Sexual ReproductionMost are hermaphroditesTwo worms join, exchange sperm, eggs in each worm are fertilized, eggs are laid and hatch within a couple weeks
Asexual Reproduction = CommonBreak into parts using fissionEach part grows/develops the missing structures through regeneration