Post on 22-Dec-2015
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Worms!Platyhelminthes, Nemtoda, and Annelida
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)
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.
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.
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.
Response
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
Reproduction
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)
Questions 1. What is a flatworm?
2. What are the three groups of flatworms?
Warm-Up
Phylum Nematoda Roundworms
Have a pseudocoelom, or "false coelom"; not a true fluid-filled, tissue-lined coelom
Body plan: "tube within a tube"
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.
Respiration, Circulation and Excretion
Rely solely on diffusion, no internal transport,
Response and Reproduction
Simple nervous system with several ganglia
Sexual: most species have separate sexes.
Internal Fertilization: Male deposits sperm inside female.
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)
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
Feeding
Circulation Closed circulatory system: blood is contained
within a network of blood vessels.
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
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.
Lab #6-Earthworm Dissection
Worms
Review for Test #5