Ms. Moore 10/18/12

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

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

 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

 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

 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.

 Reproduction:  Hermaphrodite: both male and female reproductive organs  Sexual: two worms join in a pair and they deliver sperm to each other  Asexual: fission  organism splits in two and each half grows new parts to become a complete organism

Groups of Flatworms  Turbellarians  Flukes  Tapeworms

Turbellarians  Free-living flatworms  Most live in marine or fresh water  Bottom dwellers: living in sand or mud  Planarians: “cross-eyed” freshwater worms

Flukes  Class: Trematoda  Parasitic flatworms that infect internal organs of their host; can also be external parasites.

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

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

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.

 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

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

 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 passages  elephantiasis

 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.

 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

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