Lesson 20 Flashcards
What is in Phylum Platyhelminthes?
Flatworms, the simplest of worms
“Platy” meaning flat
“helminthes” meaning worm
Name the 6 characteristics of worms…
- Invertebrates
- Ectotherms
- Bilateral symmetry
- Long narrow bodies with no legs
- Distinct anterior (front) and posterior (back)
- Simplest animals with a central nervous system
What are the three classes of flatworms?
a) Flukes (parasitic)
b) Tapeworms (parasitic)
c) Planarians (free-living)
HELPFULL OVERVIEW OF THESE THREE CLASSES (SPOILERS)
file:///C:/Users/trgan/Sync/LisA%20school/Flat%20worms%20explanation.png
Explain simply a Fluke’s and Planarian’s digestive system, and how they eat… (7 “steps”)
(1) Their digestive system has just one opening, a mouth located in the middle of the flatworm’s body
(2) The mouth is attached to a tube-like pharynx (throat)
(3) The mouthpart extends from the body, surrounds its food, and tears that food into very fine pieces.
(4) Cells lining the digestive cavity finish digesting the food and nutrients are circulated throughout the body.
(5) The digestive cavity extends into all parts of the flatworm’s body
(6) Food waste is expelled through the mouth.
(7) Cellular waste is excreted through tiny pores in the animal
Explain a Tapeworm’s digestive system, and how they eat…
They have no mouth or digestive system, but absorb
nutrients from their host.
What is a central nervous system?
A nervous system (nerves all connected) that connect to a “center” like a brain
Do flat worms have a central nervous system?
What does this give them?
Yes they do, it allows the flatworms to have the sense of taste, smell, and touch
What is the flatworms nervous system composed of?
- Ganglion: mass of nerve cells that functions like a simple “brain” in the anterior (front)
- 2 nerve cords that extend towards the posterior(back)
- Posterior and anterior nerves connect to each other by a series of transverse nerves that run across the body.
THE TWO NERVE CORDS ACT LIKE PARALLEL LINES BEING CUT BY MULTIPLE PERPENDUCULAR TRANSVERSALS, THE TRANSVERSE NERVES
Do planarians (the free living flat worms) have any way to sense light?
YES, they have 2 eyespots allowing them to sense light
Do flat worms have a circulatory system?
NO, they are instead dependent on molecules spreading throughout their body via diffusion
BECAUSE THEY ARE SO FLAT ALL THEIR CELLS ARE NEAR SOME SORCE OF WATER, EITHER THEIR DIGESTIVE TRACT, OR THE WATER THEY LIVE IN
How do flat worms reproduce?
They (the parasitic flatworms) are typically hermaphroditic (containing both male and female reproductive organs), reproducing sexually
a) Cross-fertilize with another tapeworm of the same species
b) Self-fertilize, combining their own gametes to make new organisms
Planarians (the free living flat worms) reproduce asexually
a) They do so by tearing themselves in half
- Each half regenerates its missing half, producing two genetically identical planarians.
Briefly explain a Fluke’s (a parasitic flat worm) life cycle…
They require at least two hosts, one for adult, one for larva, and spend part of their lives in snails
Explain a tapeworm’s life cycle, how they live, and reproduce…
a) They have a small knoblike head called a scolex with hooks and suckers, allowing them to attach to the intestinal wall of their host
b) Reproductive structures with sperm and egg are found in segments behind their head where eggs are fertilized.
c) Occasionally, segments in the posterior (back) of the worm detach and pass out of the host in their feces so the eggs can be dispersed.
Two hosts needed: one for adult, one for larva
Explain a Planarian’s (free living flat worm) life cycle…
They just chill and then asexually reproduce
What is phylum Nematoda?
Roundworms
