ms. moore 10/18/12. what is a flatworm? phylum: platyhelminthes flatworms are soft, flattened...
TRANSCRIPT
WORMS AND MOLLUSKS
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: fissionorganism 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 passageselephantiasis
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
