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Bio 11 Platyhelminthes Gap Notes (1)

Biology 11

Name: __________________ __________________ Date: ______________ Block: __________


Phylum Platyhelminthes (Greek: platy = “flat”, helminth = “worm”)

The “Flatworms”

Pages 311-317


  1. Background:



  • ~ 25000 known species
  • Some flatworms are free-living whereas other flatworms are completely parasitic and require a host to survive


DID YOU KNOW!!!: The longest tapeworm ever to be extracted from a human was 37 feet long

and was pulled out of a woman’s mouth!!! In whales they can grow up to 120 feet in length!!!


  1. A) Free-Living Platyhelminthes:

(Class Turbellaria)


  1. Body Plan/Structure:


  • Flatworms demonstrate a _______________________ symmetrical body plan
  • They are _________________________ flattened and lack a _____________________
  • They have a highly branched ___________________________________________. It is considered a ______________ gut because there is only one opening to it which serves the function of both the ________________ and ___________________
  • They have three germ layers:
    1. ______________________: Outside
    2. ______________________: Inside
    3. ______________________: Middle layer of tissue between the ectoderm and the endoderm
  • Though Flatworms have three germ layers they are _______________________ and have no body cavity
  • Flatworms do have ________________________ and primitive ___________________________ that are used for __________________ and ___________________
  • Flatworms are also the most primitive organisms to show _____________________
  • The head region of Flatworms contains a concentration of ____________________ called ___________________ (singular=_____________________) that resembles a primitive brain.
  • They have two ___________________________ that run from the __________________ in the head region along the ____________________ side of the worm to the tale region
  • In the head region of Flatworms are two ______________________________
  • They also have lobes on the side of their head called ____________________________


III. Feeding:


  • The free-living forms of Flatworms are ________________and ________________
  • Flatworms have a _______________________ which is connected to the ________________________ through a long muscular ___________________________
  • Small invertebrates or the remains of dead animals are taken into the mouth/anus by the muscular ____________________
  • The food is then digested in the highly branched ________________________________
  • The nutrients moves from the gut into the body cells by ______________________


  1. Respiration:


  • Respiration occurs by ___________________
  • ______________is taken up directly by the ________________ from the water or the gut
  • _______________________________ is released directly from the _________________ into the water or the gut


  1. Internal Transport:


  • __________________ and ___________________ in the gut are simply absorbed into the body cells by the process of _____________________






  1. Excretion:


  • Most undigested food is released directly out of the __________________________
  • Other waste materials diffuse from the body cells into the ____________________________ and exit out of the ________________________
  • Other undigested food is released out of tiny ____________________ that open to the water


VII. Response:


  • Flatworms are able to sense and respond to at least three forms of stimuli:
    1. Sense and respond to ____________________: The ______________________ can detect light and allow the Flatworms to respond to it
    2. Sense and respond to ____________________: ____________ on the side of their head regions can sense _______________________ in the water and allow the Flatworms to respond (like “smelling”)
    3. Sense and respond to __________________: The ____________________ on either side of the head region can sense _______________ and allow the Flatworms to respond
  • The _____________________ in the head region relay messages from the sensory organs down the ___________________________ to the rest of the body. The _______________________ can control _______________________ in the body which allow the Flatworms to ______________ or ________________.


DID YOU KOW!!!: Even though Flatworms only have primitive brains they are capable of



VIII. Movement:


  • The flatworms move across a surface using _________ on their ______________ surface
  • They can also move by contracting __________________ and _____________________ muscles that lay just below the _____________________. These muscles are controlled by the _______________________.


DID YOU KNOW!!!: Some flatworms are so muscular they can swim through the water!!!






  1. Reproduction:


  • Asexual Reproduction:
    • Flatworms can asexually reproduce through a process called __________________. The __________________ and __________________ ends hold a surface and the midsection constricts. This results in two new flatworms, one from the _________________ end of the original flatworm and the other from the _________________________ end of the original flatworm.
    • Flatworms can also ________________________ parts they have lost.


DID YOU KNOW!!!: If you cut a small piece off the tip of a flatworm’s head region and left

the wound open it will regenerate a new head in front of the old one. You can repeat the process to create a flatworm with many heads. If we were Greek we could call it a Polycephaloturbellarian!!!


  • Sexual Reproduction:
    • Flatworms are _________________________
    • After two flatworms have copulated they release sacs of fertilized __________ and attach them to a surface


DID YOU KNOW!!!: In the animal world it is much easier to be male because you generally

don’t have to take care of your offspring. Because of this some hermaphroditic flatworms demonstrate a sexual behaviour called “Penis Fencing” in which two flatworms will attack each other with their penises. The first one that can jab the other will release their sperm and thus take on the role of a male while the flatworm that has been jabbed will have their eggs fertilized and take on the role of the female!!!


  1. Ecological Roles:


  1. B) Parasitic Platyhelminthes:

(Classes Trematoda, Cestoda and Monogenea)


            Parasitic Platyhelminthes are quite a bit different than their free-living relatives. Many of these adaptations are related to the fact that they live within host organisms. Most of the final host organisms that parasitic Platyhelminthes use are vertebrates including HUMANS!!! However, they have intricate lifecycles with intermediate host organisms.

Here is a list of adaptations that make the fluke and the tape worms different than the free-living flatworms.



Class Cestoda (Tapeworms):

Ex. Taenia saginata (The Beef Tapeworm)

  • The tapeworm has an anterior end called a scolex with complicated hooks for attaching to the intestines of its host.
  • The tapeworm does not have a mouth or digestive system. Instead they bath in the pre-digested fluids of their host and absorb nutrients directly into their body cells
  • Since they live in such a harsh environment as the intestines they have a modified ectoderm called a tegument which protects them from the host’s digestive enzymes and immune responses
  • The tapeworm is hermaphroditic and has an incredibly adapted body which is a reproducing powerhouse!!!
  • The body of the tapeworm is segmented into proglottids, each containing their own group of the necessary sexual organs.
  • As the eggs in the proglottids are fertilized they are released into the human host’s intestines and eventually end up in the host’s fecal matter.
  • Lifecycle:
    • After the fertilized eggs have been released in the fecal matter of the human host the feces can be used as fertilizer, especially in underdeveloped countries with poor sewage systems etc.
    • The eggs are ingested by the intermediate host, a cow
    • The eggs mature into larva in the stomach of the cow which then burrow into the muscles of the cow
    • The beef is eaten by more humans and the larva mature into tapeworms in the intestine of the human host to start the lifecycle again.


Class Trematoda (Flukes):

Ex. Schistosoma mansoni (The Liver Fluke that causes Schistosomiasis)

  • The fluke worm has an anterior end with an oral sucker
  • Fluke worms also have a tegument like the Tapeworms to protect them from their host’s immune system and digestive juices
  • Flukes are most often hermaphroditic but in the case of Schistosoma there is a male and a female form
  • Other than these adaptations flukes show many of the same characteristics as the free-living Turbellarians
  • Lifecycle:
    • The adult fluke worm lives in the blood vessels near the intestine of a human host.
    • When it is ready to lay its eggs it pushes its way into one of the tiny blood vessels of the intestine and lays thousands of eggs
    • The sheer number of eggs causes the blood vessels to burst releasing the eggs into the intestine
    • The eggs are carried out of the human host in their fecal matter
    • In many underdeveloped countries there are no proper sewage system and the fecal matter is used as fertilizer
    • The eggs get into the water systems and mature into ciliated larva
    • The larvae swim until they find a snail intermediate host. If they do not find this snail they will die
    • The larva burrow into the tissue of the snail, feed on its tissues and asexually reproduce
    • The new larvae exit the snail and become free-swimming
    • The new free-swimming larvae burrow into the skin of humans who are swimming near them
    • A male larva and female larva will find each other and move through the human circulatory system until they reach the human liver where they mature and feed on red blood cells
    • The pair of mature Trematodes migrate to the intestines where they undergo sexual reproduction
    • The female releases the eggs into the small blood vessels of the intestines to start the cycle again.


posted by Marc Bernard Carmichael in Biology Eleven,Biology Eleven Notes,Worms and have No Comments