Saturday, September 24, 2011
Friday, September 2, 2011
POLYMORPHISM IN CNIDARIA
Cnidarians ,especially the members of order siphonophora and chondrophora exhibit polymorphism. Polymorphism means different individuals varying in structure and function form a colony which exists as a whole animal. The different forms are called zooids. Zooids can be polypoid or medusoid.
There are 3 types of polypoid zooids viz. gastrozooids ( feeding zooids ), dactylozooids ( help in defence ) and gonozooids which take part in reproduction.
The medusoid zooids can be of 4 main types : swimming bells, bracts, gonophores and pneumatophores. Pneumatophores are gas filled structures which assist the colony in floating in water. Bracts cover oyher zooids and gonophores liberate gametes. Examples of polymorphic colonies are Obelia, Physalia , Porpita, etc
There are 3 types of polypoid zooids viz. gastrozooids ( feeding zooids ), dactylozooids ( help in defence ) and gonozooids which take part in reproduction.
The medusoid zooids can be of 4 main types : swimming bells, bracts, gonophores and pneumatophores. Pneumatophores are gas filled structures which assist the colony in floating in water. Bracts cover oyher zooids and gonophores liberate gametes. Examples of polymorphic colonies are Obelia, Physalia , Porpita, etc
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