 Platyhelminthes, Nemtoda, and Annelida

 There are three major groups of worms: o 1) Flatworms (Phylum Platyhelminthes) o 2) Roundworms (Phylum Nematoda) o 3) Segmented Worms (Phylum Annelida)

 Textbook Introduction

 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.

 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.

 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.

 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

 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)

1. What is a flatworm? 2. What are the three groups of flatworms?

 Textbook Introduction

 Roundworms  Have a pseudocoelom, or "false coelom"; not a true fluid- filled, tissue-lined coelom  Body plan: "tube within a tube"

 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.

 Rely solely on diffusion, no internal transport,

 Simple nervous system with several ganglia  Sexual: most species have separate sexes.  Internal Fertilization: Male deposits sperm inside female.

 Textbook Introduction

 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)

 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

 Closed circulatory system: blood is contained within a network of blood vessels.

 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

 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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