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The hydrozoa refers to the taxonomic class of predatory animals and colonial animals that live in salt water. The members of hydozoa are related to corals and jellyfish.
Hydra belongs to the phylum Cnidaria and the class Hydrozoa.
Hydrozoa
hydrozoa
Animals in the class Hydrozoa include various species of hydroids, hydras, and Portuguese man o' war. They are mostly marine invertebrates that display a wide range of forms and lifestyles, often existing as colonial organisms with polyps and medusae.
Jellyfish belong to the phylum Cnidaria, which includes other organisms like corals and sea anemones. Within the phylum Cnidaria, jellyfish are classified into the class Scyphozoa, which includes true jellyfish, and the class Hydrozoa, which includes hydroids and smaller jellyfish species.
hydrozoa
According to Wikipedia, it is of the class "Hydrozoa": http://en.wikipedia.org/wiki/Hydra_(genus)
Hydra belong to the phylum Cnidaria and the class Hydrozoa.
They both have no class together they are two different kingdoms.
A jellyfish is the medusoid stadium of animals belonging to phyum Cnidaria, subphylum Medusozoa, which include:class: Scyphozoaclass: Cubozoaclass: Staurozoaclass: Hydrozoa (only some hydrozoans have a medusoid stadium, so not all of them have jellyfishes)class: Polypodiozoa
Kingdom, Phylum, Class, Order, Family, Genus, and Species.