Cnidaria Flashcards
(29 cards)
What was the big innovation of the cnidaria?
Cell to cell communication
What have the cnidaria lost?
choanocyte
Define choanocyte
a flagellated cell with a collar of protoplasm at the base of the flagellum, numbers of which line the internal chambers of sponges.
What substance serves as an adhesive between cells?
Collagen
What are the septate junctions made from?
connexon
Define blastulla
a hollow ball of cells that has punched in such that there is now two layers of membrane
What is the opening on the blastulla called
blastopore
What kind of symmetry is first observed in this group of cnidarians
biradial symmetry
Define operculum
a structure that covers over an arpeture
What is the organelle within the cnidocyte cell that fires the cnidocil?
nematocyst
What are the three layers in the body wall of the cnidarian polyp
epidermis, mesoglea, gastrodermis
The epitheliomuscular cells of polyp contract in which way?
longitudinal
What functions as the skeleton of the polyp
The squishy mesoglea
In which layer are the nerve cells located in?
epithelio-muscular cells
Every cnidarian has this stage, which is larval. What is it?
Planula larva
What characteristics define the planula larva
- starts on substrate
- has on end that is always forward
- has to clearly definable layers of cells
Define siphonoglyph
a ciliated groove at one or both ends of the mouth of sea anemones and some corals. The siphonoglyph extends into a pharynx and is used to create currents of water into the pharynx. This gave the cnidarians biradial symmetry
What is the first of the cnidarians, placed at the bottom of the tree, that first had biradial symmmetry?
anthozoa
Where are the gonads found in the anthozoa
In the vascular cavity (gastrodermis)
What did the anthozoa have that substituted for a skeleton
It pumps water into its self to stretch back its muscles
What is odd about the fact that there is no mesoderm in cnidaria?
they still have retractor muscles
What defines cnidarians after the anthozoa
Medusa (free swimming) and dimorphic life cycle (since we now have the medusa)
How does the medusa form?
Stroblization. Starting on substrate as polyp-like sturcture, a disk of tissue is made, another one is built on top, this cycle repeats until finally the top disk differentiates into tentacles.
How does the medusa digest and expel waste?
It only has mouth, so the food is brought in, guided through different channels and systems that remove nutrients, and then guide the waste back through the mounth.
