The Characteristics of Phylum Cnidaria

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Cnidarian Diversity
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Phylum Cnidaria
Class Anthozoa
Class Hydrozoa
Class Scyphozoa
Class Cubozoa
Corals Anemones
Hydra Portuguese Man-Of-War Stinging Limu Fire
Coral
True jellyfish
Box jellies Sea wasps
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Class Anthozoa
Subclass Hexacorallia
Subclass Alyconaria
Sea fans Sea whips Sea pens Organ pipe
coral Precious gold coral
Order Antipatharia
Order Zoanthidae
Order Actinaria
Order Scleractinia
Zoanthids
Sea anemones
Stony corals
Precious black coral Wire coral
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General Characteristics of Cnidaria

• Stinging cells
• Two stages in life cycle (polyp medusa)
• Blind sack gut
• Radial symmetry
• Diploblastic
• Hydrostatic skeleton
• Nerve net
• Many colonial, some solitary forms

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Class Hydrozoa
(Gr. hydra, water serpent)

• polyps and medusa stage, although polyp stage is
  dominant.
• gut cavity of polyp is simple, lacking a pharynx
  and not divided by mesenteries.
• tetramerous (four-part) radial symmetry.
• gonads are ectodermal (found in the epidermis).
• medusa stage may possess specialized balance
  organs called statocysts and photosensitive
  organs called ocelli.
• solitary or colonials some colonial forms highly
  polymorphic.
• includes hydroids (stinging limu), fire coral,
  pink coral, and siphonophores.

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The Cnidarian Life Cycle
The Hydrozoan Life Cycle
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Hydrozoan Colony
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Hydrozoan ColoniesStinging Limu
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Hydrozoan Medusa
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Hydrozoan Medusa
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Hydrocorals
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Fire Coral
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By-the-Wind-SailorA Floating Colony of Polyps
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Coloniality
Man-of-WarPhylum Cnidaria
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Close Up of a Portuguese Man-Of-War
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Class Scyphozoa
(Gr. skyphos, cup)

• life cycle with both polyps and medusae, but
  medusae dominate with polyp stage reduced or
  absent.
• polyp stage (scyphistoma) goes through
  strobilization to produce young medusa.
• bell margin lacks a velum.
• tetramerous ( four-part) radial symmetry.
• gut divided into a complex system of radial
  canals.
• some with a simple single mouth, but many with
  thousands of microscopic mouths at the ends of
  oral arms.
• gonads endodermal (found in the gastrodermis).
• specialized sense organs called rhopalia with
  ocelli statocysts .
• includes some 200 marine species.
• "true" sea jellies.

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Scyphozoan Life Cycle
strobila
scyphistoma
ephyra
planula
adult medusa
gametes
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Sea Jellies
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Moon Jelly Anatomy
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Class Cubozoa
(Gr. kybos, a cube)

• polyps and medusae stages, but medusae dominate
  with polyp stage reduced.
• polyp stage develops directly into medusa.
• bell margin with a velarium.
• tetramerous ( four-part) radial symmetry bell
  cube-shaped with tentacles arising from each
  corner.
• gonads endodermal (found in the gastrodermis).
• specialized sense organs called rhopalia with
  ocelli statocysts .
• includes some 15 marine species.
• includes box jellies and sea wasps.

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Seawasp
Box Jellies
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Box Jelly Anatomy
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Class Anthozoa
(Gr. anthos, flower)

• lack medusa stage entirely (polyp forms only)
• mouth with a tubular pharynx that projects inward
  into the gut
• large gut cavity divided by mesenteries that
  radiate inwards from the body wall
• gonads endodermal, borne on the mesenteries
• hexamerous (6-part) or octamerous (8-part) radial
  symmetry or biradial (modified radial symmetry
  that limits the number of planes that can divide
  the body into equal halves
• includes sea anemones, true stony corals, sea
  fans, sea pens, organ pipe coral, precious black
  coral, zoanthids

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Subclass Zoantharia Order Actinaria Sea Anemones
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Sea Anemone Anatomy
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Subclass Hexacorallia Order Zoanthidae

• No hard skeleton
• May be tough and leathery
• Shallow water forms
• Encrusting forms
• Some with zooxanthellae
• Polyp stage only

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Subclass Hexacorallia Order Antipatheria Black
Coral Wire Coral
Black coral
Wire coral
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Subclass Hexacorallia Order Scleractinia True
Stony Corals
Hermatypic- reef building, zooxanthellae

• Common species
• Acroporidae- table
• Acroporidea- rice
• Agariciidae- flat lobe, corrugated
• Faviidae- crust, ocellated
• Fungiidae- humpback, mushroom
• Pocilloporidae- lace, antler, cauliflower
• Poritidae- finger, lobe, plate

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True Stony Corals
lobe
finger
mushroom
Porites rus
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Subclass Alyconaria Octocorals

• 8 branched tentacles surrounding the mouth
• Both hard and soft forms exist
• Ahermatypic- non reef building, no photosynthesis
• Five Orders found in Hawaii
• Stolonifera
• Pennatulacea (sea pens)
• Alcyonacea (soft corals)
• Telestacae (snowflake corals)
• Gorgonacea (sea fans)

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Octocorals
Sea pen
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Organ pipe coral