Introduction to Cnidaria Jellyfish, corals, and other stingers. . .

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Introduction to CnidariaJellyfish, corals, and
other stingers. . .
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• Cnidarians are incredibly diverse in form
• Yet, these diverse animals are all armed with
  stinging structures called nematocysts
  (cnidocytes)
• The name Cnidaria comes from the Greek word
  "cnidos
• Many thousands of cnidarian species

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• Fossil Records
• A few mineralized coral-like fossils have turned
  up in the Cambrian Period
• Identifiable corals began an evolutionary
  radiation in the Early Ordovician
• Scleractinian corals appeared in the Middle
  Triassic, about 15 million years after the
  Permian extinction.

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• Scleractinian became the dominant hermatypic
  (reef-building) organisms in shallow tropical
  marine habitats.
• Corals are sensitive to changes in light,
  temperature, water quality, and salinity

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Cnidarian TAXONOMY

• There are four major groups of cnidarians
• Anthozoa, which includes true corals, anemones,
  and sea pens
• Cubozoa, the amazing box jellies with complex
  eyes and potent toxins
• Hydrozoa, the most diverse group with
  siphonophores, hydroids, fire corals, and many
  medusae and
• Scyphozoa, the true jellyfish.

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CNIDARIAN Morphology
Versus polyp
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Features

• Two tissue layers with nerve and muscle tissues
• Nematocysts structures contained in special
  cells called cnidocytes or cnidoblasts that can
  act in both offense and defense
• Two main life forms free-swimming medusa (e.g.,
  jellyfish) or stationary polyp (e.g., anemone)

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Introduction to the Anthozoa

• Anthozoans are probably the most famous
  cnidarians they include the corals that build
  great reefs in tropical waters, as well as sea
  anemones, sea fans, and sea pens.
• True corals living today did not appear until the
  middle Triassic, at about the same time that the
  first dinosaurs were evolving

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Introduction to CubozoaThe Box Jellies

• They look like your basic jellyfish, but they can
  swim pretty fast, maneuver around things, and see
  fairly well despite not having a brain.
• Cubozoans have a square shape when viewed from
  above.
• They also have four evenly spaced out tentacles
  or bunches of tentacles and well-developed eyes
• Chironex fleckeri

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Introduction to the Hydrozoa

• The best-known hydrozoan is Hydra. Hydra never
  goes through a medusoid stage, and spends its
  entire life as a polyp.
• Most hydrozoans alternate between a polyp and a
  medusa stage -- they spend part of their lives as
  "jellyfish" which are hard to distinguish from
  scyphozoan jellyfish.
• The "Portuguese man-o'war" and "by-the-wind-sailor
  s" that often wash up on beaches are examples of
  these unusual colonial hydrozoans.

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Introduction to the Scyphozoa the true jellyfish

• Scyphozoans include most of the jellyfish other
  similar organisms
• Their stings may cause skin rashes, muscle
  cramps, or even death.
• Jellyfish range in size from a mere twelve
  millimeters to more than two meters across.
• The largest is Cyanea arctica, which may have
  tentacles over 40m long!

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