PHYLUM: CNIDARIA

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PHYLUM CNIDARIA
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Classes of Cnidaria

• Class Hydrozoa (e.g., Hydra, Obelia)
• Class Scyphozoa (e.g., Aurelia)
• Class Cubozoa (e.g., cube jellies)
• Class Anthozoa (anemones and corals)
• Subclass Hexacorallia (sea anemones, hard corals)
• Subclass Octocarallia (sof corals)

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General Characteristics

• Entirely aquatic mostly marine, but with a few
  freshwater species
• may be solitary or colonial
• Metazoan, with true tissues.
• Diploblastic two germ layers
• outer cell layer known as ectoderm (epidermis),
• inner cell layer known as endoderm
  (gastrodermis),
• with a non-cellular mesoglea between.

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General Characteristics

• The internal body space (gastrovascular cavity)
  lined with gastrodermis
• has a mouth, but no anus (incomplete digestive
  tract)
• Possess cnidocytes with special cell organelles -
  nematocysts, used for defense and offense

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General Characteristics cont.

• Phylum exhibits polymorphism
• Metagenesis- alternation of generation
• Polyp (often sessile) and the medusa (free
  swimming).
• The polyp stage reproduce asexually, while the
  medusa stage usually reproduces sexually
• Reproduction is asexual by budding and/or sexual,
  producing a ciliated planula larva

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Figure 13.02
Two general body forms
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Class Hydrozoa

• solitary or colonial
• alternation of asexual polyps and sexual medusae

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Figure 13.09
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Life Cycle of Hydra
SEXUAL REPRODUCTION
ASEXUAL REPRODUCTION
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Hydra with Bud
Ovary
Bud
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Hydra with Gonads
Testes
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Hydra c.s.
Gastrovascular cavity
Epidermis
Mesoglea
Gastrodermis
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Figure 13.09
Obelia Life Cycle
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Obelia - Medusa
Gonad
Tentacle
Gastrovascular cavity
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Obelia Hydroid colony
Gastrozoids Hydranth
Gonozoids Gonangium
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Obelia Hydroid Colony
Gonozooid
Hydrozooid
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Gonionemus
Gonad
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Physalia Portuguese Man-O-War - a colony, not
an individual
It is not a jellyfish!!
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Class ScyphozoaTrue Jellyfishes

• polyp stage reduced or absent
• bell-shaped medusae
• margin of bell with eight notches which are
  provided with sense organs
• all marine

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Aurelia - Medusa
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Aurelia - Planula larva
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Aurelia - Scyphistoma
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Aurelia - Strobila
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Aurelia - Ephyra
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Class AnthozoaSea Anemones and Corals

• all species occur as polyps only, no medusae
• gastrovascular cavity partitioned by at least
  eight septa with nematocysts
• Solitary or colonial
• all marine.

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Some Hydrozoans
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Figure 13.07
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Figure 13.15a
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Figure 13.15b
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Some Scyphozoans
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Jellyfishes
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Figure 13.16
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Figure 13.17
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Some Anthozoans
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Sea Anemones
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Figure 13.25
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Figure 13.29
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Corals
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Figure 13.32
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Figure 13.33a
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Figure 13.33b
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Figure 13.28
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Figure 13.26b
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Figure 13.26c
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Phylum Ctenophora

• The Combjellies

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General Characteristics

• Biradial symmetry
• Eight rows of comb plates
• Tentacles possess colloblasts
• Triploblastic (three cell or germ layers)
• Mesoglea (loose mesenchyme) is jelly-like
  material strews with fibers and amebocytes and
  contains true muscle cells
• Aboral sense organ (statocyst)
• Digestive system mouth, pharynx, stomach,
  branched canals and anal pore
• Monoecious, with both eggs and sperm produced
  from endodermal lining of digestive canals
  beneath comb plates

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Figure 13.36
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Figure 13.36a
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Figure 13.38
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Figure 13.38a
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Figure 13.38b
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Figure 13.35
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