Notes - Platyhelminthes and Nematodes

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1 Notes - Platyhelminthes and Nematodes - These two phylum are composed of. However, the worms we are going to look at are not common. Both of these phyla are composed of unsegmented worms. That is, these worms are not divided into or like an earthworm and are considered less developed ( ) than earthworms. Unsegmented worms have definite organs contained in a fluid filled body cavity ( ). Phylum Platyhelminthes - Platyhelminthes considered the simplest animals with and. They have more developed organ systems than either sponges or. Flatworms are carnivorous,, or parasites. There are three kinds of flatworms; turbellaria, trematoda, and. Turbellaria flatworms. Ex. planarian. ingest organisms in through their mouth and into a long muscular tube called a. The pharynx leads to the gastrovascular cavity (intestine), which spreads throughout the length of the planarian, and uses to breakdown the food. The food can throughout the planarian to all cells needing nutrition. Waste food is expelled back out the mouth. - Flatworms lack any kind of respiratory or systems. Due to their flat body plans, diffusion can transport all gases and nutrients needed. Many flatworms also contain flame cells, which are used to expel extra through pores in the skin. Flatworms have a much more developed nervous system than Cnidarians or Porifera. They have a definite head with a (simple brain) and a definite nerve cord with branches running the length of the organism. They have ocelli ( ) that are light sensitive and help direct the flatworm towards light as well as touch sensors and chemical sensors in their skin to help direct to food and hiding places. - Flatworms move using and muscles to wiggle their way around. - Reproduction occurs both sexually and asexually. Most flatworms are. The worms will pair up and fertilise each other s eggs with sperm. Asexual reproduction often occurs through (being cut or split and each piece regenerating into a new worm). 1

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3 Trematoda (flukes) and Cestoda ( ) -Some Platyhelminthes are and feed off or host cells. They have little to no digestive tract as it is not needed. In most cases the host organism has already predigested most to all of the food. Ex. and. - Parasitic flatworms have little to no system as responding to stimuli (light or chemicals) is not needed inside of their host. - Parasitic flatworms are usually not hermaphroditic and have a much more complex life cycle than their non-parasitic cousins. Trematoda life Cycle Use your textbook (not picture) page 573 to fill in detailed notes of the blood fluke life cycle. 3

4 Cestoda Life Cycle - Tapeworms are parasitic flatworms that absorb predigested food from their host s intestines. See life cycle to side diagram next page. - Once full of eggs the break off and burst releasing eggs that exit with feces. If food or water that is contaminated with eggs is eaten by cows, fish, pigs or other intermediate hosts, then the eggs hatch. The larvae burrow into and form cysts. If a human eats raw or not completely cooked meat the larvae become active and enter the human s to start the cycle over. 4

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7 Phylum - round worms simplest organisms to have a fully developed digestive system. That is, they have a, intestines, and an for expulsion. Roundworms are found in water, soil, and from the tropics to the polar regions of earth. - Roundworms can be carnivorous and eat smaller organisms such as; algae, fungi, or. Parasitic roundworms can attach to plant roots and feed of the plant juices or may infect animals and feed in the intestines. - Like, roundworms breathe and excrete metabolic wastes through their body wall. They have no circulatory system and so rely on diffusion for transport. They have a simple system with several ganglia in the head region. They control muscular movements using a few nerve chords that run the length of the body. - Reproduction occurs through internal fertilisation. Parasitic roundworms have complex life cycles like parasitic flatworms did. - is a parasitic roundworm that affects humans. There are many species like ascaris that affect horses, pigs, deer, chickens, dogs, and cats. Collectively they are called. 7

8 Role in Nature - Both flatworms and roundworms have little positive influence on humans. Most help break down dead and rotting organic material or eat organisms smaller than they are. However, the parasitic unsegmented worms have the largest impact on humans. Hundreds of millions of people are infected by roundworms each year., like the guinea worm, are terribly painful and affect many outside of North America. The life cycle is the same as ascaris except hookworms feed of intestinal blood. is a roundworm that causes trichinosis. Most people are infected by eating improperly cooked. The larvae burrow through the intestines into the blood and move about the body until they burrow into muscles and form cysts (painful!). 8

9 - worms are threadlike worms that travel in the system instead of the blood. They cause blockages in the lymph and lead to elephantiasis. 9