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PHYLUM PLATYHELMINTHES
Biology 11
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What is a flatworm?
Acoelomates
Thin, solid bodies
Can be 1mm to several meters
14,500 species
Marine, freshwater, and moist habitats on land
Ex. Tapeworms, flukes, planarians
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Flatworms
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1. Class Tubellaria (Planaria)
Soft, flattened bodies covered in cilia
Live in aquatic or moist environments
Scavengers
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2. Class Trematoda (Flukes)
Parasitic: therefore, they have a tough outer
covering and two suckers to anchor to a host and
feed at the same time.
Example: Schistosoma (liver fluke).
Lung Fluke
Zombie Snail
mailto:http://animal.discovery.com/tv-shows/monsters-inside-me/videos/the-lung-fluke.htmmailto:http://www.youtube.com/watch?v=Go_LIz7kTokhttp://animal.discovery.com/tv-shows/monsters-inside-me/videos/the-lung-fluke.htm
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3. Class Cestoda (Tapeworm)
Parasitic: live
in digestive
tract of host.
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Organization
3 true cell layers (endoderm, mesoderm, ectoderm)
Simple organs (cephalization, excretory, pharynx,
ect.)
Acoelomates
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Motility
All
Bilateral symmetry
Mobile
Planaria
Move by gliding over a slime track they secrete
Anterior
Dorsal
Posterior
Ventral
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Feeding
Planarians / Flukes
Extracellular digestions: enzymes secreted by mouth
A muscular tube, the pharynx, is extended out though
the mouth. The food is sucked in through the pharynx
and passes into the intestine and digestive glands.
Tapeworm
Intracellular digestion: tapeworms absorb the digested
nutrients of their hosts, so they have no need for a
mouth
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Digestion and Excretion
Planarians / Flukes
Incomplete digestive system: food enters through the
same opening by which undigested wastes leave.
Extracellular digestion: enzymes secreted onto slow-
moving or dead prey.
Excretory system consists mainly of FLAME CELLS; small,
bulb-like structures that remove water and chemical
wastes through the body pores by using beating cilia.
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Digestion
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Excretion
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Digestion/ Excretion Con’t.
Tapeworms
No digestive system, since they absorb nutrients
already digested by their host. The SCOLEX is a knob-
shaped head with hooks or suckers or both, with which
the tapeworm attaches to its host.
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Nervous System
Planaria / Flukes
Two anterior ganglia serve as a simple brain
(cephalization)
A ladder-like network of nerves runs the length of the
body
React to light, chemical, food
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Nervous System Con’t.
Tapeworm:
The nervous system is reduced
The main nerve center, ganglion, is in the scolex
Smaller nerves travel down the body to muscular and
sensory ending
Some nerves are only temporary
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Reproduction
Planaria / Flukes
Asexual: through fragmentation and regeneration
Sexual: individuals are hermaphrodites, but individuals
cannot fertilize their own eggs. Eggs are laid in a
protective cocoon and take 2-3 weeks to hatch
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Planaria Reproductive Picture
https://www.youtube.com/watch?v=wn3xluIRh1Y
https://www.youtube.com/watch?v=wn3xluIRh1Y
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Reproduction Con’t.
Tapeworm
Behind the SCOLEX is a region
from which PROGLOTTIDS are
produced and eventually shed.
PROGLOTTIDS are body sections
that contain a complete
hermaphrodite reproductive
system.
Tapeworms have at least two hosts
in their life cycles
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Proglottid
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Circulation
Planarians / Flukes / Tapeworms:
None
Diffusion of nutrients to body cells
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Overview
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