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Platy-helminthes and Nematoda. Common Name. Platy-helminthes. Nematoda. Roundworm. Flatworm. Tapeworm. pinworm. P lanaria. Fluke. Symmetry. Platy-helminthes. Nematoda. Bilateral. Bilateral. Platy-helminthes and Nematoda.

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common name
Common Name




  • Flatworm









  • Bilateral
platy helminthes and nematoda1
Platy-helminthes and Nematoda
  • Tissue Complexity: eumetazoa (all animals except the sponges, placozoans and mesozoans)
  • Germ Layers: 3
feeding digestion
Feeding/ Digestion



Complete digestive tract

  • Gastrovascular cavity
respiration circulation excretion
Respiration, Circulation, Excretion



Respiration: Diffusion

Circulation: Diffusion

Excretion: Nephridia.

  • Respiration: diffusion
  • Circulation: Diffusion
  • Excretion: Flame cells (nephridia)
response movement reproduction
Response, Movement, Reproduction



Response: Simple, ganglia.

Movement: Hydrostatic skeleton.

Reproduction: Hermaphroditic. External and internal fertilization.

  • Response: Simple, ganglia and 2 eyespots.
  • Movement: Hydrostatic skeleton.
  • Reproduction: Hermaphroditic. External and internal fertilization.
other unique characteristics
Other Unique Characteristics



Parasitic (must be inside host to reproduce)

  • No digestive tract
  • Advanced reproduction (penis fencing)
big idea 1 the process of evolution
Big Idea 1: The Process of Evolution



To complex organisms:

Feeding/digestion: gastrovascular cavity and complete digestive tract

Respiration: diffusion

Circulation: diffusion

Excretion: flame cells and nephridia

Response: Ganglia

  • To complex organisms:
    • Symmetry: bilateral
    • Tissue complexity: eumetazoa
    • Germ Layers: 3
    • Gut openings: 2
  • To bacteria:
    • Respiration: diffusion
    • Circulation: diffusion
evolutionary characteristics
Evolutionary Characteristics
  • Lowest organism with a head, centralized nervous system, complex reproductive organs, mesoderm, and a bilaterally symmetrical body
big idea 2 biological systems
Big Idea 2: Biological systems

Efficient resource gathering

Efficient conservation of energy


One cell thick epidermis

Thin body allows for minimal energy expenditure


Parasitic, do not need to go far to obtain nutrients

Breathe through skin, no respiratory system taking up space and expending energy

  • Platy-helminthes
    • Absorb digested material directly through diffusion
    • Thin bodies allow for waste to diffuse out of the skin
  • Nematoda
    • Most are parasitic, obtain nutrients by burrowing into the intestine or lungs of animals
innate behavior
Innate Behavior



Ganglia allow response to light, heat and touch

Some studies show they have chemoreceptive pores, allowing response to chemical signals

Seek out hosts in which to feed and reproduce

  • Have eyespots, allowing them to respond to changes in light
  • Predatorial-use pharynx opening to suck food particles into gastrovascular opening
  • Innately feed on blood and tissues of host
learned behavior
Learned Behavior



While nematodes have been shown to respond to chemical and tactile stimuli, all research has been inconclusive in showing any memory of stimuli

  • Have been shown to respond to classical conditioning (an experiment involving associating bright light with an electric shock led to flatworms responding to light as if being electrocuted)
  • Offspring and worms that were fed crushed 1st generation worms also displayed this learned reaction, indicating chemical memory
cooperative behavior
Cooperative Behavior



Hunt in groups

Gather in groups and feed

Gene causing this is related to the Neuropeptide Y receptor gene in humans

Mating is through touch

Textile signal

  • Trematode flatworm parasites exist in cooperative colonies consisting of big reproducers, which release hundreds to thousands of clonal offspring daily, and specialized soldiers that defend the colony.
big idea 4 biological systems interact in the environment
Platy-helminthesBig Idea 4: Biological Systems Interact ~ in the environment
  • Investigation of polyclad chemical defense mechanisms revealed that several polyclads contain strong toxins such as tetrodotoxin. These findings suggest that flatworms are warning of their unpalatability and that their visual predators, fish, will quickly learn to avoid them by recognition of their distinct and bright colour pattern. Experiments performed by Hing P. Ang and Leslie J. Newman provide the first experimental evidence of aposematiccolouration in pseudocerotid flatworms.
  • Trematodes usually have a pair of suckers for crawling and clinging to the host's tissue
  • restricted to living in a wet environment, such as in freshwater, sea or in moist terrestrial environmen
  • Some flatworms have primitive light-sensing "eyes" that allow them to move either towards or away from light, while other species have different types of sensors on their bodies, including chemical, balance, and water movement receptors
nematoda big idea 4 cont
Nematoda (Big Idea 4 cont.)
  • They are found in almost every imaginable habitat , including terrestrial (land-based), freshwater, and saltwater ecosystems , as well as within other organisms as parasites.
  • Nematodes can be herbivorous, carnivorous, or parasitic, and include both generalists (who make use of a wide variety of resources) and specialists (who make use of only particular resources)
big idea 4 biological systems interact role in environment
Big Idea 4: Biological Systems Interact ~ Role in environment



  • decomposition and nutrient cycling, where they are often the intermediate decomposers that partly break down organic materials so that they can then be dealt with by bacterial decomposers
  • parasitic or commensal relationships with plants and animals
      • addaptations that allow for certain host environments allow the parasitic organisms to thrive