Download The Phylum Cnidaria

Cnidarians
“The guys with the stinging
Cnidarians
• Finally, we see a pie
that can be sliced!
• Cnidarians actually
exhibit radial symmetry
in which similar body
parts can be grouped
around a central axis.
• Here we also observe a
large jump on the
evolutionary scale:
tissues that perform
specific functions.
Phylum Cnidaria
The Classes of Cnidaria are:
• Anthozoa- Sea Anemones and Corals
• Hydrozoa- Hydra
• Scyphozoa- “true” jellyfish
• Cubozoa- “box-shaped” jellyfish
• Ctenophora- non stinging Cnidarians:
 Comb Jellies
**There are over 10,000 species of
Cnidarians
All About Cnidarians
Interesting Stuff
1. Jellyfish fact: Jellyfish have been around for more than 650 million years which
means that they outdate the dinosaurs and the sharks.
2. Jellyfish fact: Different species of jellyfish can be found in all the worlds’
oceans. Jellyfish can even be found in freshwater.
3. Jellyfish fact: A species of jellyfish, the Box jellyfish (sea wasp) kills more
people than any other marine creature.
4. Jellyfish fact: The worlds largest known jellyfish can reach a diameter of 2.5 m/
8ft and their tentacles can grow to be half the length of a football field.
5. Jellyfish fact: Jellyfishes uses jet propulsion to make their way through to
oceans of the world. Some swim while others mostly drifts with the currents.
6. Jellyfish fact: Some species of jellyfish contain a lot of protein and are thought
to be able to play a large role in ending hunger and malnutrition.
7. Jellyfish fact: Jellyfish is able to reproduce both sexually and asexually during
different parts of their lifecycles
8. Jellyfish fact: what enables them to survive is their stinging tentacles that
protect them from being preyed upon.
Characteristics of Cnidarians
• Two cell layers (epidermis, gastrodermis,
separated by jelly-like layer called
mesoglea)
• Stinging tentacles
• Sac-like digestive system
• Radial symmetry
• Tentacles are arranged in a circle around
the mouth
• Nerve net- simple nervous system
• invertebrate
Radial Symmetry
Radial
Compass jellyfish
Anatomy
A. Polymorphism- Cnidarians have
more than one body form:
1. Polyp
2. Medusa
Polyp Form
• Tube with tentacles
around the mouth
• Sessile
Coral polyp
Polyp (sea anemone)
Polyp (Hydra)
Medusa
• Umbrella shape
• Tentacles around mouth
• Motile, Free-swimming
Cnidocytes-Stinging Cells
• Within the cnidocyte is the
nematocyst (which is like a
capsule)
• The capsule has the stinging
structure which is a hollow
thread (Filament) with barbs
• Most contain a toxin
• Very small, but discharged in large
numbers
• Usually the sting is only strong
enough to kill zooplankton or tiny
fish
• But there are exceptions!
• Discharged nematocysts,
stinging cells used for
defense and prey
capture, have been the
plague of more than fish.
• Stings from certain
jellyfish have resulted in
death in a matter of
hours, especially for
infants.
Habitat
Aquatic:
• Most are
Marine
• A few are
freshwater
Two Tissue Layers
1. EPIDERMIS –
OUTER LAYER
2. GASTRODERMIS –
STOMACH CAVITY
MESOGLEA – JELLY MATERIAL
BETWEEN TISSUE LAYERS
ABUNDANT IN JELLYFISH TO
HELP THEM FLOAT
One Opening System
FOOD IN
Food enters through the
mouth and is digested in thee
cells.
Wastes are excreted
through the mouth.
Sperm and eggs are released
through the mouth.
WASTES,
GAMETES
OUT
Feeding
1. Carnivores
(predators)
2. Process of feeding
Lion’s mane eats
a. Tentacles sting prey with
another jelly!
nematocysts
b. Tentacles grab prey
c. Prey pulled into mouth
3. Prey moved into gastro-vascular cavity (GVC)*
4. GVC makes enzymes, breaks down food, extra-cellular
digestion
5. Undigested food moves back out of mouth
Process of feeding
3. Prey stuffed into gastrovascular cavity (GVC)*
4. GVC makes enzymes, extracellular digestion
5. Undigested food back out
mouth
*incomplete digestive tract (no anus)
Lion’s mane jellyfish eating
Respiration
• Via diffusion
• Body is two cell
layers thick
Response
•
•
•
•
No nervous system
No brain
Nerve net around mouth
Nerves cover the body but do not tell the
difference between body parts.
Locomotion
A. Medusa- motile, free-swimming
B. Polyps- sessile, attached to hard
substrate
Exceptions:
1. Hydra tumbles on tentacles
2. Sea anemones glide on pedal
disc
Reproduction
1. Asexual
budding
2. Sexual
a. Medusae release sperm & eggs
b. Larvae are free-swimming
Life Cycle of a Typical Cnidarian
• Alternation of Generations
• One form is the polyp (a cylinder with
the closed end attached to the substrate
and the open end with the mouth and
tentacles directed upward)
• The other form is the medusa, freeswimming, with the mouth underneath
(like a jellyfish)
Life Cycle of a Typical Cnidarian
Hermaphrodite
sexual
asexual
Alternation of Generations
Ecological Role
A. Predators and prey
B. Neurotoxins in medical research
C. Coral – jewelry, building, reefs
(surfing!)
D. Coral reefs - habitat for many different
species, great biodiversity, protect
coastline
E. Symbiosis with other organisms
Do Now
1. Explain how the jellyfish is adapted for
floating?
2. How do jellyfish capture and digest their
prey?
3. Describe how a typical jellyfish reproduces.
4. How does the adult form of a jellyfish differ
from that of a sea anemone?
5. How does a sea anemone obtain its food?
6. How does the sea anemone respond to
stimuli?
Class Anthozoa: Sea
Anemones
Class Anthozoa: Corals
FORMATION OF CORAL
REEFS
CORAL REEFS ARE BUILT BY MILLIONS OF CORAL
POLYPS OVER THOUSANDS OF YEARS
EACH POLYP CREATES A “CUP” OF CALCIUM
CARBONATE TO LIVE IN
CORALS REPRODUCE ASEXUALLY BY BUDDING,
THIS PROCESS HELPS COLONIES TO GROW
POLYPS ARE
CONNECTED
OLD SKELETONS
FORMATION OF CORAL
REEFS
CORALS ALSO REPRODUCE SEXUALLY ONCE A YEAR
BY RELEASING SEX CELLS INTO THE WATER.
THIS HELPS TOP ESTABLISH NEW COLONIES
HARD CORALS
REEF BUILDERS – USE
CALCIUM FOR SKELETON
EACH SPECIES HAS A UNIQUE
COLONY & CUP DESIGN
EXAMPLES:
BRAIN,
ELKHORN,
STAR
Class Scyphozoa: True Jellyfish
Fried egg jelly
Giant Jelly off Coast of Japan
Remember you can only touch
the tops!!!
Jellyfish Humor
Portuguese
Man 0’ War
(a Hydrozoan),
NOT a true
jelly fish
Portuguese Man 0’ War
Tentacles of Physalia physalis
Chironex fleckeri
the Box jelly fish
Carukia barnesi: the badest of the bad!
Irukandji syndrome:
A sting from this little guy can cause the following:
“It begins with a mild sting, followed by severe lower back pain,
muscle cramps in arms, legs, stomach and chest. It causes
sweating,
anxiety, nausea, vomiting, headaches and palpitations, and has
also
been known to cause cardiac failure.”
Portuguese Man o’ War
vs. Box Jelly fish
COMB JELLIES
PHYLUM CTENOPHORA
BASIC CHARACTERISTICS:
“CTEN” REFERS TO FUSED
PLATES OF CILIA LOOK
LIKE A “COMB” STRUCTURE
DO NOT CONTAIN
STINGING CELLS
USE CILIA TO
FILTER WATER
TENTACLES ARE
STICKY TO CATCH
FOOD
Comb jellies: Ctenophora
Similar to cnidarians in
most
respects.
Nearly 100 species.
Contain cilliary combs
which assist in prey
capture and mobility.