Class Hydrozoa
Polyps are small and may occur
as solitary or colonial
A. Body plan
B. Colony Growth
C. Life History
Polyps are small
and may occur
as solitary or
colonial
Colonies grow in one of 3 main patterns
Hydrorhizal
Monopodial
Sympodial
Colony Growth Forms
Medusae are small and not as structurally
complex as the scyphozoan medusae
Characteristics of Class Hydrozoa
(Polyp and Medusa are prominent in some species)
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Siphonophores:
Polymorphism within colonies of Hydrozoa
Composed of clonally produced multicellular zooids
Highest division of labor & most precise organization
bio.fsu.edu/.../images/Female-Hydractinia.jpg
Velella velella (by-the-wind-sailor)
Characteristics of the Anthozoa
(Sessile, inactive lifestyle)
ClassAnthozoa
A.  Diversity
B.  Body plan
C.  Cloning
D.  Symmetry
E.  Life History
Diversity of Class Anthozoa
•  Hexacorallia
Actinaria (anemones)
Scleractinea
SubClass Hexacoralia
Order Actinarea
(corals)
•  Octocorallia
Alcyonacea
(soft corals)
Gorgonacae
(sea fans etc.)
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Anthozoan Polyp
Symmetry in Cnidaria compared to other animals
What morphological characteristics associated with a
larger polyp size?
Nemanostella
Anthopleura elegantissima
Clonal reproduction in anemones
Internal or external budding
Pedal laceration
Fission
Tentacular brooding
§  The Aggregating Anemone
§  Clonal wars
§  Competition for space,
§  Self-nonself recognition
§  Research shows individuals have specialized roles
• Ayre, David, and R. K. Grosberg, 2005 Animal Behavior
• Francis, L, 1976 Biological Bullentin 150: 361-376.
70: 97-110.
§  Acrorhagi (non-feeding tentacles)
Division of Labor
Inflates, contacts , nematocyst fire and stick; scarring
§  Most acrorhagi wins
§  Scout
§  Warrior
§  Reproducer
§  Reserve
§  Free edge
If attacked, a warrior often retaliates
If significant injury, retreat by pedal locomotion
•  Multiple attackers at once can cause extensive injury and death
•
•
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Diversity of Class Anthozoa
Anemone Line
SubClass Hexacoralia
Order Scleractinea
§  As a result of the clone
war, an anemone free
zone is established.
§  Two separate colonies
can co-exist, separated
by only a few
centimeters.
Stony Corals
Class Anthozoa:
SubClass Octocorallia
soft corals
Class Anthozoa:
SubClass Octocoralia
Soft corals
Soft Corals
Stoloniferan
corals
Class Anthozoa:
Sea Pens
SubClass Octocoralia Sea Pansies
Sea Fans
Life cycle of Anthozoans Consists of a
planula that settles to become a juvenile
Less complex.
Is this the
Ancestral
Life Cycle?
Which came first
Polyp or medusa?
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Two Scenarios for the evolution
Of the Cnidarian Classes
Generalized life cycle of Cnidarians
In what way are life cycles altered in Hydrozoa,
Scyphozoa, Anthozoa and Cubozoa?
18s r-DNA, mt DNA, & new morphological studies
support idea that the Anthozoa is the basal group
Immortal Jellyfish
Turritopsis nutricula,
the immortal jellyfish,
is a hydrozoan whose
medusa form can
revert to the polyp
stage after becoming
sexually mature.
Involves Stem cells
and
Trans-differentiation
of cells
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