Explain The Classification Of Phylum Cnidaria?

It is classified on the basis of polypoid phase in the life cycle. They are classified as – hydrozoa, scyphozoa and anthozoa. The hydrozoa are also known as water animals. They are marine and occur in fresh water also. They may occur alone or in colonies. They show alternation of the generations. They also show the phenomena of polymorphism. The sexual form medusa has velum and bears a narrow ridge. The gastro vascular cavity is present which does not contain septa. The sex organs are ectodermal in origin with the liberation of sex cells to the outside environment. The scyphozoa are also known as cup shaped animals. They are mainly marine. They occur alone as bell shape without the presence of velum and are known as jelly fishes. Their poly form is not fully developed and is absent in some cases. They have mesogloea which is larger in size. The gastro vascular cavity is present which does not contain septa. The sex organs are endodermal in origin and liberate the sex cells to the gastro vascular cavity. Anthozoa are also known as flower cnidaria. They are mainly marine. They occur alone or in colonies. They have poly form with the absence of medusa. The gastro vascular cavity is present which does contain septa and divides in the different compartments.