worms and mollusks
DESCRIPTION
Ms. Moore 10/18/12. Worms and Mollusks. What is a flatworm?. Phylum: Platyhelminthes Flatworms are soft, flattened worms that have tissues and internal organ systems. They are the simplest animals to have 3 embryonic germ layers , bilateral symmetry , and cephalization . - PowerPoint PPT PresentationTRANSCRIPT
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WORMS AND MOLLUSKS
Ms. Moore 10/18/12
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What is a flatworm?
Phylum: Platyhelminthes
Flatworms are soft, flattened worms that have tissues and internal organ systems.
They are the simplest animals to have 3 embryonic germ layers, bilateral symmetry, and cephalization.
Acoelomates: without coelom (fluid-filled body cavity, lined with tissue from mesoderm
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Flatworms: Form and Function Feeding:
Carnivores or Scavengers ; can be parasitic
Digestive cavity with single opening (mouth)
Pharynx: extends outside the mouth and pumps food into digestive cavity (gut)
Food diffuses from the digestive cavity into all other body tissues
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Respiration, Circulation, and Excretion: Since their bodies are so flat and thin,
many flatworms do not need a circulatory system to transport materials (use diffusion).
No gills or respiratory organs; no heart, blood vessels, or blood.
Flame cells: specialized cells that remove excess water from the body; filter and remove ammonia and urea using pores of the skin
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Response: Ganglia: groups of nerve cells that
control the nervous system (no brain) Eyespot: group of cells that can detect
changes in the amount of light in their environment
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Movement: Cilia on the epidermal cells help glide
through the water. Muscles controlled by the nervous
system help to twist and turn to react to environment.
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Reproduction: Hermaphrodite: both male and female
reproductive organs Sexual: two worms join in a pair and
they deliver sperm to each other Asexual: fissionorganism splits in two
and each half grows new parts to become a complete organism
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Groups of Flatworms
Turbellarians
Flukes
Tapeworms
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Turbellarians
Free-living flatworms
Most live in marine or fresh water
Bottom dwellers: living in sand or mud
Planarians: “cross-eyed” freshwater worms
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Flukes
Class: Trematoda
Parasitic flatworms that infect internal organs of their host; can also be external parasites.
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Tapeworms Class: Cestoda
Long, flat, parasitic worms that are adapted to life inside the intestines of their hosts.
Scolex: contains suckers or hooks; attaches
Proglottids: segments that make up most of worm’s body; contain male and female reproductive organs Youngest proglottids are at the anterior end and the largest
and most mature are at t he posterior. After eggs have been fertilized, proglottids break off and release zygotes that are passed out of the host in feces/
Testes: fertilize eggs of other tapeworms or of self
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What is a Roundworm? Phylum: Nematoda
Roundworms are slender, unsegmented worms with tapering ends; Range in size from microscopic to a meter in length
Pseudocoelom: false coelom (only partially lined with mesoderm
Digestive tract with two openings—mouth and anus (posterior opening of digestive tract) “tube within a tube”: inner tube is digestive tract and
outer tube is body wall Food moves in one direction
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Roundworms: Form and Function
Feeding: Carnivorous: eat small animals by latching
on to them with grasping mouth parts and spikes
Scavengers: eat algae or decaying mater Consume bacteria and fungi
The free living roundworms tend to be more complex than parasitic roundworms.
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Respiration, Circulation, and Excretion Diffusion through body walls
Response Simple nervous systems with several ganglia; sense
organs that detect chemicals given off by prey or host
Movement Muscles extend length of body; function as
hydrostatic skeleton
Reproduction Sexually with male and female worms Internal fertilization
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Roundworms and Human Disease
Trichinosis-Causing Worms Caused by Trichinella roundworm Worms burrow into intestine walls and
females release larvae that travel through the bloodstream and live in organs and tissues of host’s body
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Filarial Worms Found in tropic regions of Asia; live in
blood and lymph vessels of birds and mammals (humans)
Transmitted host-to-host by biting insects like mosquitoes
Large numbers could block lymph passageselephantiasis
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Ascarid Worms The cause of malnutrition of more
than 1 billion people worldwide. Ascaris lumbricoides usually
spread by eating vegetables that are not washed properly.
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Hookworms 25% of the world’s population is
infected with these worms Eggs hatch outside the body and
mature in the soil Use tooth-like plates to burrow
into skin of an uncovered foot and live in bloodstream
Suck blood and cause weakness and poor growth
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Research on C. elegans
DNA sequence has been mapped out (97 million bp)
Help us find out how eukaryotes become multicellular and how multicellular animals are similar and different
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