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Phylum Platyhelminthes

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What does Platyhelminthes mean
flat worm
What is the level of organization
organ system
What kind of body cavity do they have
acoelomate
What are the three classes of platyhelminthes?
Turbellaria, trematoda and cestoda
what are turbellaria
Planaria, free living worms
what are trematoda
flukes, mostly parasitic
what are cestoda
tapeworms, all parasitic
how big are planaria?
microscopic to 60 cm (2 feet)
what is planarias habitat
mostly freshwater
charecteristics about planaria
bottom dwellers, nocturnal, carnivourous/scavengers
why do planaria have a triangle head
to be aerodynamic
what are eyespots
contain black pigment and sensory cells to detect light, no lens
what are auricles
sensory areas for touch, contain chemical receptors for food
what is on the ventral surface
covered with cilia (traction) and mucas cells (traction/capture prey)
where is its mouth
1/2 way down, pharynx extends from it
where is its genital pore
2/3 way down, exchange sperm/lay eggs
What are the parts of the nervous system
ganglia,longitudinal nerves, transverse nerves, peripheral nerves
what is the ganglia
brain, cluster of sensory cells that sorts stimuli
what are longitudinal nerves
run anterior to posterior
what are transverse nerves
connect longitudinal nerves
what are peripheral nerves
extend outwards from longitudinal nerves
what are the parts of the muscular system
longitudinal muscles, circular muscles, diagonal muscles and parenchymal muscles
what do longitudinal muscles do
shorten
what do circular muscles do
lengthen
what do diagonal muscles do
bend side to side
what do parenchymal muscles do
run dorsal to ventral, push animal downward
describethe excretory system
runs through mesoderm, many tubes, run from anterior to posterior, from these pores open to dorsal surface, smaller tubules branch off and end with a "flame cell"
what is a flame cell
contain cilia which beat to pull fluid from mesoderm into tubes and out pores
what are the steps of ingestion
capturing prey, break prey into smaller pieces, pharynx sucks bits of food into intestine
how do they capture prey
slime cells on ventral surface secrete mucas which gets sprayed onto prey to immobilize them
how do they break prey into smaller pieces
gland cells inside intestine secrete digestive enzymes which get sprayed onto prey (partially digests it)
Describe intestine structure
3 branches, 1 anterior 2 posterior, these further branch into smaller tubes which increase surface area for digestion and absorbtion of food
how does digestion work
gland cells in the intestine secrete digestive enzymes, nutritive cells have flagella which mix the food/enzymes, nutritive cells then engulf food and finish digestion inside vacules, food then difuses to all parts of the planaria
what are the nutritive cells similar to in cnidarians
epitheliodigestive cells
how does elimination work
pharynx extends, animal sucks in water to fill the intestine, once filled the muscles contract to force contents back out of pharynx
what kinds of reproduction is there
sexual and asexual
how does asexual reproduction work
regeneration- worm constricts into middle and pulls apart, each piece will develop new halves
how does sexual reproduction work
1- exchange sperm through the genital pore
2- sperm goes to the copulatory sac to mature
3- once mature, the sperm traves through oviducts towards eggs
4- zygote then travels back towards genital chamber, along the way yolk (food) and capsule is added
5- encapsulated zygote released into water to eventually hatch in 2-3 weeks
what are the barriers parasites have to overcome
1- reaching and penetrating new hosts
2-surviving against defenses of host (white blood cells)
what adaptations have parasites used to overcome
1- structures for attachment (flukes have suckers, tapeworms have suckers, hooks and teeth)
2-resistant outer body coverings (tapeworms have cuticles)
3- complex reproductive systems (tapeworms have reproductive organs in each of their body segments, can self fertilize)
4- intricate reproductive cycles (flukes usea variety of intermediate hosts to reach primary host, snail to fish to human, hard to get rid of)
what are cuticles
tough,secreted coverings which resist WBC, chemicals, ect
what traits have parasites lost
1- mouth/digestive cavities(food difuses through the skin, food is already digested for them)
2- muscles/cilia/mucas (host provides everything, dont need to go anywhere)
3- nerves/brain (no need to locate mates, food, home, ect)