35-2 Cnidaria and Ctenophora

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35-2 Cnidaria and Ctenophora

• 2 phyla of radially symmetrical
  invertebrates.
• More complex than sponges
• have tissues and some simple
  organs.
• All are aquatic.
• Most live in the oceans.

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Phylum Cnidaria (cnidarians)

• Freshwater hydra
• Jellyfish
• Coral

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Freshwater Hydra

• Molecular Expressions Science, Optics You -
  Olympus MIC-D Pond Life Digital Movie Gallery -
  Hydra (Coelenterata)

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Jellyfish
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Coral
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Body Structures

• 2 forms ( stages of life)
• V shape polyp sessile, like
  sponge
• Bell shape medusa swimming form
• p. 696 35-3

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Medusa and Polyp
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Body Structures

• 2 cell layers (also known as germ layers)
• epidermis outer layer of cells
• gastrodermis inner layer of cells
• Mesoglea jellylike substance between layers
• Gastrovascular cavity hollow gut
• Mouth single opening
• Tentacles flexible extensions around mouth

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Feeding and Defense

• All have cnidocytes
• Specialized cells for defense and capturing
  prey.
• Each cnidocyte has a nematocyst, which has a
  long filament coiled inside it.
• When cnidocyte is triggered, the nematocyst
  pushes filament out capture prey with poison
  then tentacles push prey into gastrovascular
  cavity through the mouth. Enzymes digest the
  food, lining of gut absorbs nutrients. The waste
  products out through mouth.

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Cnidocyte

• To the right is a nematocyst prior to firing and
  after.  You can see the stinging portion which
  would embedded in the skin.

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Nervous System

• Nerve net is a diffuse web of nerve cells.
• No brain.
• Enables cnidarians to respond to stimuli in
  the environment.
• Coordinates feeding and traveling.

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Classification

• 3 classes under the phylum Cnidaria.
• 1.   Hydrozoa medusa form or polyp form or
  both.
• 2.   Scyphozoa most of life as medusa form.
• 3. Anthozoa only as polyp form.

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1. Class Hydrozoa

• 3,700 species (fresh water and salt water
  which means marine habitats)
• Live as colonial organisms
• Exs
• A.Obelia all polyp forms
• B. Portuguese Man-of-War live as a colony
  of polyps and medusa forms
• C. Fresh water hydra

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Obelia
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Portuguese Man-of-War
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Hydra

• Only as polyp forms
• Not colonial
• 1 to 4 cm in length
• Most are white or brown, some green because of
  symbiotic algae that live in it.
• Attach to rocks or water plants in ponds
• Can move from one place to another

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Asexual Reproduction

• Done by buds during warm weather

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Sexual Reproduction

• Only in the fall when temperatures are cool
• Eggs produced in ovaries
• Sperm produced in testes
• Either male or female or hermaphrodite
• Fertilized egg develops into embryo which then
  forms into new hydra

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2. Class Scyphozoa

• Cup animals
• Dominant life form is medusa
• 200 species
• Jellyfish (Aurelia)
• 2 cm to 4 m

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Life Cycle of Jellyfish
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3. Class Anthozoa

• Flower animals
• 6,100 marine species
• Sea anemones and corals
• Only in polyp form

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Sea Anemones

• Attach to rocks in coastal areas
• Feed on fish and smaller animals that come
  near their tentacles
• One exception the clownfish has a symbiotic
  relationship with the anemone. The tentacles of
  the anemone protect the clownfish from predators
  and the clownfish drives away other fish that
  would eat the anemone.

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Corals

• Live in colonies
• Cements its calcium carbonate skeleton to each
  other. When it dies, other polyps continue to
  live on this foundation. Thousands of years
  later, a coral reef is formed, but only the top
  layer is living. This coral reef provides food
  and shelter for fish and other invertebrates.
  Coral reefs are usually in shallow depths, and in
  warm, clear waters. The coral reefs have
  symbiotic algae that live in them. This is one
  reason why they are in shallow depths, so that
  the algae can photosynthesize.

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Corals
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Corals
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Phylum Ctenophora

• 100 marine species
• Comb holders
• comb-like rows of cilia
• look like jellyfish, so sometimes called comb
  jellies

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 Difference from Cnidarians

•  Do not pulsate through water but use cilia to
  move
•  Do not have cnidocytes but have colloblasts,
  which secrete sticky substance, which sticks to
  prey.
•  Have sensory structure called apical organ at
  one end of body.
•  Most are hermaphrodites
•  They are bioluminescent which means they are
  able to produce light.

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Comb Jellies
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Review p.704 1-19, 21-25

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