Phylum Cnidaria I Flashcards
What are the three types of cnidocytes (stinging cells)?
1) Nematocysts
2) Spirocysts
3) Ptychocysts
What is the cnidocil?
The cnidocil is the “trigger” that shoots out stinging mechanisms in hydrozoans and scyphozoans only.
What are the two body types found in Phylum Cnidaria?
1) Polyp
2) Medusa
List the characteristics of the medusa form:
- Free-swimming
- Oral system downfacing
- Saucer or bell shaped
- Thick mesoglea
- Relatively soft-bodied
List the characteristics of the polyp form:
- Attached to a substrate by aboral surface
- Thin mesoglea
- Hard skeleton
- Cylindrical shape with tentacles surrounding the mouth
Define “diploblastic”
Made of two tissue layers:
1) Ectoderm
2) Endoderm
Define and or describe the “mesoglea”
- Jelly-like layer
- Provides shape and buoyancy
- Found in the epidermis and gastroderm
What’s the difference between worms and cnidaria if they’re all just bags of water?
Worms have segmented bags of water comprising their bodies. CIrcular muscles help the worm move via contraction.
What does fluid in the gastrovascular cavity do for polyp movement?
Acts as the hydrostatic skeleton
How does movement occur with a hydrostatic skeleton?
- Pressure of fluid causes movement
- Extension and contraction of tentacles and body (think of crunches).
- Circular muscles
What acts as the hydroskeleton in medusae movement?
The mesoglea
Muscles operate with or against mesoglea pressure in medusae movement?
Against pressure: swimming is done by jet propulsion of water against mesoglea pressure.
Why are Phylum Cnidaria muscles not true muscle?
They are epithelially derived, not mesodermal.
This makes their muscles different than other metozoans.
