Zoology 1121
Laboratory 4
Phylum Cnidaria
Quiz
I Phylum Cnidaria
1. Primarily marine, so hydrostatic environment
2. 2 basic forms: polyp or medusa
3. Form can be motile free-swimmers or immobile (sessile) or both
For Phylum Determination:
1. Be diploblastic (2 layers only) with a primitive indistinct middle
layer
2. Radial symmetry – no matter from which angle you slice trough it,
all halves lo the same.
3. Polyp, medusa, polymorph of either. [polymorph-means ‘having many
different forms’]
4. Gastrovascular cavity with one opening [mouth (called a –stome)]
and no other opening [called an anus]
5. Tentacles with nematocysts
6. Must meet all above to be classed in this phyla [memorize these]
-Common names: jellyfish, sea anemones, hydras, corals
For Class Determination (if found to be in Phylum)
1. Body form is sessile polyp . . . . . . . . . . . . . . . . . . .
. . . . . . . . . Class Anthozoa
2. Body form is motile medusa . . . . . . . . . . . . . . . . . . .
. . . . . . . . Class Scyphozoa
3. Body form alternates from polyp to medusa . . . . . . . . . . .
. . . . Class Hydrozoa
Cnidarians
1. Two well defined tissue layers:
a. Epidermis
b. Endodermis [has specific name “gastrodermis”]
2. Forms gastrovascular cavity with single opening where foods enters
and refuse leaves
3. 3rd jelly-like, indistinct layer between the epi- and endoderm called
mesoglea.
4. Greater cell differentiation in cnidarians than sponge. 1st
to see “tissue” level of organization.
5. Diploblastic –2 layers
6. Triploblastic – 3 layers
7. Hydrostatic skeleton – outside water turns to slime
8. Nematocysts – stinging elements for food gathering and defense.
1. Found in a specialized
cell called a cnidoblast.
2. Something touches cnidoblast
then this causes the nematocyst to be ejected.
3. Nematocysts – look like
harpoons tied to rope
4. Toxins injected
9. radial symmetry
1. Central axis and body
radiates around it. (See slide)
2. RS – for sessile and
floating life
Cnidarian Brains
1. No brain yet, simple re-active nerve net
2. Call generically as having a nervous system, this phyla first to
have one
3. Neurons: just like other cells except have dendrite and axon specialization
for communication
4. Technically, it's a Nervous Net – b/c large number of these
neurons connect to each other. Found exclusively in this
phylum.
5. Complex behaviors due to this simple net
6. Both epidermal and endodermal layers have contractile processes
(equiv. to muscles)
7. Ex, freshwater hydra:
1. endoderm: contractile
processes encircle latitudinal (circular –side to side)
2. epiderm: contractile
processes runs longitudinal axis (up-down)
Cnidarian Evolution
1. Trends with this phylum to more complicated ones
a. tissue layers
b. reproductive organs
c. nervous systems
d. limited mobility
3 Classes of Phylum
1. Class Anthozoa
2. Class Scyphozoa
3. Class Hydrozoa
Class Anthozoa
1. Exclusively polyps
2. Primarily sessile
3. Two types based on hard or soft body types
a. Hard Body – corals
b. Soft Body – sea anemones
Class Scyphozoa
1. Free-swimmers (medusa)
2. Umbrella shaped
3. Mesoglea very pronounced across this Class – hence name, jellyfish
Class Hydrozoa
1. Polymorphic: either polyp or medusa or alternating
2. Sexual or asexual reproduction
a. Asexual- formation of buds [think- sprouting
off another adult looking form from yourself]
b. Sexual – (in hydra) – results of gametes produced
through reduction division
1. occurs in ovaries and
testes of gonadal tissue
2. Gonads look like swellings
on the stalk of the hydra
3. Ovaries closer to basal
end, testes closer to tentacles [think: t in testicles and also in tentacles]
4. Ovaries: produce single
egg (common theme from now on in all phyla)
a. egg released and remains outside hydra
5. Testes: produces many
sperm (common theme seen as well)
a. sperm swims to egg and fuses for fertilization
3. Gastrovascular cavity
1. One type of cell found in this endoderm will
release digestive enzymes directly into the cavity.
(they stain really darkly)
2. These enzymes break down food.
3. Extracellular: stage of digestion that occurs
outside the cell.
4. Once extracellular digestion rips apart food
into smaller pieces, a second set of gastrovascular cells
take up these bits through
phagocytosis. This is called intracellular digestion, since it occurs inside
the cell.
4. Epidermal Layer
1. most cells here have specific name of epotheliomuscular
cells
2. other specialized cells called cnidoblasts with
nematocysts
3. fastest mechanical movement of any living creature
Cnidarian Behavior
1. All animals have these chemicals
2. Found in blood, lymph, etc
2b. This called Receptor - Mediated behavior
2c. Conserved evolution - we see this on so many levels and so many
organisms througout the animal kingdom
3. Ligand –a specific key used to open up a receptor
a. In this instance both
chemical are said to be ligands
b. Behavior is described
as an animal’s response to environmental stimuli.
c. Physiological unit of
behavior is the motor system
d. Technically: sensory
system brings in information for processing and motor system effects (i.e.,
brings about)
an output based upon the sensory information.
e. Here though, the sensory
receptors are classified as accessory units to the motor system
4. Cnidarian motor system
1. when prey moves by tentacles,
they are stung with nematocysts
2. this causes release of
chemicals from fluids of prey
3. two amino acids are present:
a. gluathione
b. tyrosine
4. Specialized cells on tentacles act as “sensory neurons” for either
of 2 amino acids
5. Specific behaviors results from either /or
6. Also, concentration gradients comes into play here
7. Tyrosine: causes moth to close and gastrovascular to compress so
that it touches prey to maximize digestion
8. Gluathione: causes effector muscles to contract. Swings tentacles
to mouth and mouth to open.
9. Must be G then T for correct feeding behavior to occur
Cephalization: concentration of sensory cells toward front of
body.
Why?
1. Defense
2. food capture
3. Closer to brain
Difference between a medusa hydra and a medusa jellyfish
1. based on placement of gonads
a. gonads inside velum:
then Hydra
b. gonads outside velum:
then jellyfish
Jellyfish
1. has planula larva
2. They find home. Grows as polyp
3. then each layer becomes new jellyfish
Know fig 5-3
IMPORTANT TERMS:
Schyphozoa
Anthozoa
Hydrozoa
epidermis
gastrodermis
mesoglea, hydrostatic
skeleton
radial symmetry
nematocysts
cnidoblast
polyp
tentacle
mouth
testis
gastrovascular cavity
ovary
bud
extracellular digestion
intracellular digestion
nerve net,
nerve cell
sensory cell
receptor molecule
ligand
E. Discussion of Experiment
1. Two chemicals, glutathione (a tri-amino acid found in the body fluids of virtually all animals) and tyrosine (a single amino acid also ubiquitously found) are applied to a hydra. There would be no response to these extremely small chemicals if there were no protein receptors for these chemicals embedded in the plasma membranes of some of the nerve cells in the Hydra. When the chemical interacts with the receptor molecule, the plasma membrane becomes depolarized and results in an electrical impulse. These impulses result in muscle contractions that cause the tentacles to contract, or the mouth to open, etc. Receptors are very specific (lock and key model) and will only interact with one chemical. The receptors for gluathione are located on the tentacles only. The receptors for tyrosine are located inside the gastrovascular cavity. Glutathione triggers the first component of the feeding response while tyrosine triggers the second. Together, these ligands stimulate the entire feeding response of the hydra.
Answer these questions:
1. What hypothesis was being tested?
2. Why were the responses to Glutathione and Tyrosine different?
3. What does this tell us about feeding behavior in Hydra?
4. What is the difference between sensory cell (receptor cell) and a receptor molecule?
5. Why are there not receptor molecules for Tyrosine on the tentacles?
6. What is ligand/receptor interaction?
7. Why is it important and beneficial to have feeding behavior?
8. Why should such behavior be coordinated?
9. Why does the behavior include closing the mouth?
10. Do Hydra have other behaviors and what would you predict they would be?
11. Do Hydra possess other receptors to things besides these two chemicals?
12. Do humans have the same kinds of receptors?
13. Why did we look at behavior in such a "primitive" animal?
14. What were the controls for the experiment? Why did we add the brine shrimp?
15. Why did the brine shrimp cause the observed response?
16. What were some variables that were probable ignored in the experiment?