platyhelminthes, nemtoda, and annelida. there are three major groups of worms: o 1) flatworms...
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Worms!Platyhelminthes, Nemtoda, and Annelida
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Major Groups There are three major groups of worms:
o 1) Flatworms (Phylum Platyhelminthes)
o 2) Roundworms (Phylum Nematoda)
o 3) Segmented Worms (Phylum Annelida)
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Platyhelminthes Flatworms : have tissues
and internal organ systems.
Flatworms are acoelomates, meaning without coelom.
coelom: fluid-filled body cavity
They have right and left sides, and most have enough cephalization to have what is called a head.
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Respiration, Circulation and Excretion
Most cells are in contact with external environment, so they rely on diffusion.
No gills, heart, blood or blood vessels.
Some have flame cells: specialized cells that remove excess water and wastes.
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Respone Head encloses several ganglia: groups of nerve
cells
Not complex enough to be called a brain
Many have eyespots: groups of cells that can detect light.
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Response
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Reproduction Most are hermaphrodites: both male and
female reproductive organs
Sexual reproduction: two worms join and deliver sperm to each other; eggs are then laid in clusters
Asexual reproduction: fission - organism splits in two and each half grows to form a complete organism
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Reproduction
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3 Types of Flatworms Turbellarians: free-living flatworms, most live in
marine or fresh water. (planarians)
Trematoda: parasitic flatworms, most flukes infect the internal organs of their host. (flukes)
Cestoda : long, flat, parasitic worms that are adapted to life inside the intestine of the host. (tapeworms)
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Questions 1. What is a flatworm?
2. What are the three groups of flatworms?
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Warm-Up
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Phylum Nematoda Roundworms
Have a pseudocoelom, or "false coelom"; not a true fluid-filled, tissue-lined coelom
Body plan: "tube within a tube"
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Feeding Digestive tract has two openings – mouth and
anus
Many free-living forms are predators with grasping mouth parts to catch and eat small animals.
Other eat decaying matter, and several types are parasitic and cause disease in humans.
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Respiration, Circulation and Excretion
Rely solely on diffusion, no internal transport,
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Response and Reproduction
Simple nervous system with several ganglia
Sexual: most species have separate sexes.
Internal Fertilization: Male deposits sperm inside female.
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Phylum Annelida Segmented Worms
Ring-like appearance, or "segmented" body parts
Many have bristles, (setae), attached to each segment
Have a true coelom that is lined with tissue came from mesoderm (middle layer)
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Feeding Many use a pharynx; some have sharp jaws to
attack prey.
Earthworms: pharynx pumps food and soil into a tube called the esophagus.
Food enters the crop where it is stored, and then through the gizzard, where it is ground into small pieces
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Feeding
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Circulation Closed circulatory system: blood is contained
within a network of blood vessels.
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Respiration Aquatic annelids have gills
Gill: organ specialized for the exchange of gases underwater.
Earthworms take in oxygen and release carbon dioxide through their moist skin
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Reproduction Most reproduce sexually.
Two worms attach to each other, exchange sperm, then store it.
When eggs are ready, the clitellum secretes a mucous ring into which eggs and sperm are released and fertilization takes place.
The ring slips off the worm and forms a protective cocoon from which young worms hatch weeks later.
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Lab #6-Earthworm Dissection
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Worms
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Review for Test #5