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 Scyphozoa• Alternate between

polyp and medusa stage

• Medusa stage usually larger and more developed than the polyp

• The familiar jellyfish

• Small in size, usually mistaken for algae

• Most alternate life stages between medusa and a polyp

• Often form colonies

• true corals, anemones, sea pens, sea fans

• Lack a medusa phase.

Remember your mnemonic

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 CnidariansHow many tissue layers do you see developing?

2

The Tissue layers

http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&ved=0CCUQFjAB&url=http%3A%2F%2Ffaculty.mwsu.edu%2Fbiology%2Fjon.scales%2FCourses%2FZoology%2Flectoutlines%2F8_cnidaria.ppt&ei=PZP2TvWHJ-ixsALm0ui2AQ&usg=AFQjCNHSJGry_TVVRdnjBdX-WKKwLKsG6g

DigestionSingle 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?

• 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

No thanks

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-netMyoepithelial = cells with characteristics of muscle cells and epithelial (think skin) cells.

Nerve net vid

• Start at 3:21

• http://www.youtube.com/watch?v=S5xvagTFrv4&feature=related

Life Cycles and Reproduction Asexual

BuddingMedusa budsPolyp buds

SexualGonadal tissueGametes (sperm or egg)Fertilization, embryogenesisPlanula 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 polypOften form colonies

Scyphozoa

Alternate between polyp and medusa stageMedusa 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 firingHydrozoan 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