The Cnidarians!
Forget the “C””
They are everywhere!
Habitat
•
•
•
•
Found in every ocean and sea
Freshwater as well
Shallow and deep ocean environments
Very successful group
The 2 Body types
Polyp
Medusa
The 2 Body types
Polyp
• Corals and anemones
• Tentacles and mouth
face UP and the other
side is affixed to a
substrate or a colony of
the same species
• Sessile in this form
Medusa
• Jellyfish
• Upside down- Tentacles
and mouth face DOWN
• Motile in this form
The 2 Body types
• Most Cnidarians alternate between both body
types
• Some sea anemones and corals do not
alternate
• Questions: Which body type are the corals
and anemones?
• Polyp
3 Classes of Cnidarians
Anthozoa
• true corals,
anemones, sea
pens, sea fans
• Lack a medusa
phase.
Remember
your
mnemonic
Scyphozoa
• Alternate between
• Small in size,
polyp and medusa
usually mistaken for stage
algae
• Medusa stage usually
• Most alternate life
larger and more
stages between
developed than the
medusa and a
polyp
polyp
• The familiar jellyfish
• Often form colonies
Hydrozoa
Cladogram based on
molecular systematic data
Where are they on the tree?
What are the
two levels of
organization
you see
displayed in
Cnidarians?
Radial
Symmetry and
true tissues
Radial symmetry
Tissues
• simplest organisms at the tissue grade of
organization
• Their cells are organized into true tissues.
• Cnidarians are like bags made of two cell layers.
The outer layer, or epidermis, contains the
cnidocysts, the stinging cells that are
characteristic of the phylum.
• The inner layer, or gastrodermis, lines the gut. In
between epidermis and gastrodermis is the
mesoglea, a layer of jelly-like substance, which
contains scattered cells and collagen fibers. The
mouth is often, but not always, surrounded by a
ring of tentacles.
• The mesoglea is not the same as a mesoderm!
Diploblastic Cnidarians
2
How many
tissue layers
do you see
developing?
The Tissue layers
&e
&u
olo
lec
njB
Digestion
Single opening serves as
entrance and exit for:
• Food + nutrients
• Waste
• Both intra and intercellular
digestion. Enzymes are
released into the body cavity
and help break down food.
• Food is then engulfed by cells
lining the gut in a process
called phagocytosis
How to put a Cnidarian in the tree
continued…
• Do they have a coelom???
• What is a coelom?
• Fluid filled sac formed in
mesoderm
• Therefore only triploblastic
animals can have one
• Allows organs to grow off
the body wall of an animal
• No. They are Acoelomate
Circulatory system?
No thanks
• Question: Why do Cnidarians not have/need a
circulatory system?
• Cells are close enough contact with water for
simple diffusion to absorb and remove nutrients
and gasses
• Diffusion enhanced by water being moved by cilia
in the Gastrodermis and/or muscular movements
Level of Cephalization
•
•
•
•
First organisms to develop nervous system
Nerve-net , nerves spread throughout the body
Beginnings of centralization of nerves
Certain species developed ocelli –basic light
sensing organs
• Nerve centralization around these ocelli begins to
occur.
The nerve-net
Myoepithelial = cells with
characteristics of muscle cells and
epithelial (think skin) cells.
Nerve net vid
• Start at 3:21
• http://www.youtube.com/watch?v=S5xvagTFr
v4&feature=related
Life Cycles and Reproduction
Asexual
Budding
Medusa buds
Polyp buds
Sexual
Gonadal tissue
Gametes (sperm or egg)
Fertilization, embryogenesis
Planula larvae
Dimorphic (two phase) life cycle
The different classes of cnidarians
modify this lifecycle
Show me in the chart how the following modify this life
cycle phase
Anthozoa
Lack a medusa phase.
Hydrozoa
Most alternate life stages between medusa and a polyp
Often form colonies
Scyphozoa
Alternate between polyp and medusa stage
Medusa stage usually larger and more developed than
the polyp
Sperm and
egg
released
Add ploidy slide (2n 1n etc.)
• Video: ..\..\..\Lesson
Videos\Biology
11\Portugese Manowar.flv
• Notes: Which class of
Cnidarian is the creature in
the video?
• What life stage is it in?
• What are some special
adaptations this organism
has developed?
Portuguese Man-o’war
or Bluebottle jellyfish
There’s me surfing in Australia where I learned
about stinging nematocysts first hand.
3 times
Nematocysts (ouch!)
• Imagine trying to
capture live prey
without the aid of teeth,
a jaw and hard
protective body parts.
• Video ..\..\..\Lesson
Videos\Biology 11\How
Do Jellyfish Sting_.flv
Nematocysts
Nematocyst firing
Hydrozoan capturing prey with
nematocysts
How Nematocysts function
• An unused nematocyst is held within a cell
known as a nematocyte
• Most nematocytes are located on the
tentacles of the Cnidarian, which are the
primary food capturing part of the body.
• Nematocysts are continuously produced.
• They are not reused following discharge and it
is energetically costly to produce them.
• Therefore its best for a Cnidarian to fire only
when necessary.
• Touch or chemical stimuli may cause firing.
• Osmotic pressure is thought to cause firing.
• Spines and a twisting motion help the
nematocyst to puncture the skin and inject
the venomous tubule.
• Cnidarians have developed many different
and complex chemicals to inject.
Irukadnji – The box Jellyfish
• ..\..\..\Lesson Videos\Biology 11\Box
Jellyfish - Irukandji.flv
Draw some Cnidarians:
Draw a Polyp and Medusa
Include and label the following in your drawing:
Endoderm cells
• Gastrodermis
Ectoderm cells
• Tentacles
• Nematocysts
ALSO INCLUDE: mouth/anus
The Tissue layers
Gallery walk
• ..\..\..\Lesson Videos\Biology 11\Cnidaria
Ability To Move.mov.flv
• Take notes on anything we can use to fill out
the 7 ways to survive sheet
• Brainstorm the answers as a class
• Watch the first 9 minutes:..\..\..\Lesson
Videos\Science 8\optics\Eyes - Evolve - History
Channel.flv