Ctenophora

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Ctenophora Cnidaria
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Cnidaria

• Cnidarians are eukaryotic
• They belong to kingdom Animalia
• Cnidarians are all aquatic, most are marine but
  some are fresh water (Hydra)
• They get their name from nematocysts, which are
  specialized cells that carry stinging organelles
  called cnidocysts
• There are approximately 11 000 different species
  of Cnidarians
• They evolved over 650 million years ago as some
  of the first multicellular organisms

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Body Structure
The basic structure of a polyp (left) and hydroid
(right)
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Body Structure

• Cnidarians bodies usually consist of a double
  germ layer called the gastrodermis and epidermis.
  The separating layer is non cellular and is
  called mesoglea.
• The double layer encloses a gastrovascular cavity
  which opens beside the mouth.

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Body Structure

• The outer epidermis contains sensory nerve cells,
  gland cells, stinging cells (nematocysts), and
  contracting cells (epitheliomuscular)
• Cnidarians have no sides, their bodies have
  radial symmetry
• Radial symmetry means when cut along their
  central axis the halves would be mirror images of
  each other

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Movement and Nutrition
Structure of Nematocysts
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Movement and Nutrition

• Cnidarians swim using jet propulsion (pulsing of
  the bell)
• They have tentacles containing nematocysts
  (stinging cells) that sting prey and are used for
  protection
• The tentacles then bring the prey to the mouth
• They feed on larger protists, worms, crabs, fish
  and other cnidarians

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Movement and Nutrition

• The nematocyst pierces the epidermis of its prey
  or predator and the hollow thread-like filament
  releases venom
• The thread-like filament then recoils inside the
  capsule of the nematocyst

The nematocyst entering the epidermis of its prey
or predator
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Life Cycle
Diagram of the life cycle of a Jelly fish
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Life Cycle and Reproduction

• Cnidarians produce both sexually and asexually
• One stage of a cnidarians' life they are medusae
  (free swimming, ex. Jelly fish)
• The other stage is Polyp (found attached to docks
  or floats ex. Hydra)
• The two stages appear very different but really
  the medusae structure is an upside down form of
  the polyp

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Life Cycle and Reproduction

• Most cnidarians go through both stages in their
  lifespan, however corals and sea anenomes stay in
  the polyp stage their entire life
• Cnidarians either possess male or female gonads
• The eggs are fertilized internally, they develop
  as a planktonic planula larva, until it settles
  in a suitable spot and then it buds to form a new
  colony
• The colony of polyps then bud medusae organisms
  continuing the life cycle

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Digestive System of Cnidarians

• Cnidarians ingest their food into the
  gastrovascular cavity where it is broken down by
  digestive enzymes
• Solid waste is excreted through the opening to
  the gastrovascular cavity which serves as both a
  mouth and anus
• Gaseous waste is excreted through diffusion

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Four Main Classes OfCnidarians
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Class Anthozoa

• Sea Anemones and Corals

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Class Scyphozoa

• Jellyfish

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Class Cubozoa

• Box Jellies

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Class Hydrozoa

• Obelia Portuguese Man
  o War Aequorea

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Ctenophora
Example of a bioluminescent comb jelly
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Ctenophora

• Ctenophores have eight rows of fused cilia along
  their sides
• They are similar to cnidarians, yet lack
  nematocysts, instead they use sticky cells called
  colloblasts to capture their prey in a
  suction-like manner
• They are bioluminescent (meaning they can give
  off light)
• Many ctenophores are transparent

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References

• http//encarta.msn.com/media_701610521_761555168_-
  1_1/Life_Cycle_of_a_Jellyfish.html
• http//www.ucmp.berkeley.edu/cnidaria/cnidaria.htm
  l
• http//www.ucmp.berkeley.edu/cnidaria/cnidaria.htm
  l
• http//library.thinkquest.org/26153/marine/cnida.h
  tm
• http//www.reefland.com/rho/0505/images/shimek4.gi
  f