Transcript Cnidaria lab_2014_b 7323KB Apr 16 2015 11:39:46 AM

INTRO TO CNIDARIA
FISH310
Spring 2013
Defining Characteristics
• secretion of complex intracellular organelles
called cnidea
• All have basic radial symmetry
• Planula larvae - free-swimming, flattened,
ciliated, bilaterally symmetric larva
• Possess only 2 layers of living tissue (epidermis
and gastrodermis) with mesoglea in between
• All have tentacles around the mouth
• A single opening to the digestive system.
Body Plan
oral-aboral axis
Hydrozoans
• ~3,000 mostly marine
species
• Typically small with
polyp and medusa
stage
• Members of this class
include: Hydroida,
Siphonophora,
Hydrocorallina
• Gastrodermis lacks
cnidea
• No cells in mesoglea
Portuguese Man O’War!
http://video.nationalgeographic.com/video/manowar_portuguese
Hydrozoans
• Examine colonial polyp
• Try to identify species using dichotomous key
• Note colony form, polymorphism, life history
Anthozoans
Anthozoan
Evolution!
• Never have a medusa stage
• Today we will look at the external and internal
anatomy of a sea anemone
Sea Anemone’s at War!
Acrorhagi
Today we will see these defensive
structures in our Anthopleura dissections
•Hollow spherical protrusions covered
with potent nematocyts
•Function in defending territory
Cnidea (nettle/stinging thread)
• Multiple Functions: food collection, defense and
locomotion.
• Can be specialized for wrapping around small objects,
sticking to surfaces, penetrating surfaces, or secreting
proteinaceous toxins.
• 3 major categories of cnidea:
– Spirocysts – anthozoans (corals/sea anemones)
– Ptychocysts – tube anemones
– Nematocysts – most common and well studied (over 30 types;
many types in a single species)
• Cells that contain cnidea are called cnidoblasts
• Discharge triggered by chemical/physical stimulation of modified
cilia (cnidocil). Takes only 3 ms!
• Primary force behind expulsion is osmotic pressure, although the
exact mechanism remains uncertain. Different types of cnidea may
operate by different mechanisms.
Nematocysts!
Nematocyst animation!
Nematocysts firing under a microscope!
LET’S FIRE SOME!
Making a Wet Mount
• 1. Gather a thin slice/piece of whatever your specimen is.
If your specimen is too thick, the coverslip will wobble on
top of the sample like a see-saw and you will not be able
to view it under high power
• 2. Place ONE drop of water directly over the specimen. If
you put too much water, the coverslip will float on top of
the water, making it hard to draw the specimen (Plus too
much water is messy)
• 3. Place the coverslip at a 45 degree angle with one edge
touching the water drop and then gently let go.
Performed correctly the coverslip will perfectly fall over
the specimen. Try to avoid air bubbles.
Coral Reefs
Algal Symbionts
Check out the algal symbionts in our
local species, Anthopleura
elegantissima
Zooxanthellae – dinoflagellate
of the genus Symbiodinium
Zoochlorellae- single celled green
algae
Acontia
Let’s look at the acontia of
our local species, Metridium
• Thin filaments extending from the
middle lobe of the mesenteries
loaded with nematocysts
•Extend outside body through small
pores in body wall
• Function in offense, defense, &
digestion
Scyphozoa
• True jellyfish ~200 species
• Mainly medusoid morphology
Fig. 1. Life cycle of the
moon jellyfish Aurelia
aurita. A Mature female
medusa (30 cm in
diameter) carrying
planula larvae (red
arrow) in brood pouches
in the oral arms. B
released, free-swimming
planulae (0.2-0.3 mm). C
Polyp (1-3mm). D
Beginning strobilation. E
Advanced strobilation. F
Young Ephyra (3-5mm).
G Ephyra, 4 weeks after
release (8-10mm).
The Moon Jelly Life
Cycle!
Scyphozoan Sensory Structures
• Sensory organs include:
– Statocysts – balance organ
– Ocelli – light receptor
• Statocysts and ocelli are
contained within structures
called rhopalia
• Cubozoans also have highly
advanced sensory structures
(lensed eyes)
CLEAN UP
• Thoroughly wash all dissection tools and trays
• Dispose of animal remains in biohazard
container in the fume hood
• Rinse slides & toss coverslips in sharps
container
• Make sure your scopes are clean and turned
off
• Present your worksheet
Feeding
Anemone Feeding Video
Hydra Feeding Video
Jellyfish Feeding
Anemone Feeding on Jellyfish