hydra is a genus of small, fresh-water animals.

anatomy animals aquarium asexually background basal battle biology body bud budding cell class cnida cnidaria cnidocytes disc education educational endoderma epidermis freshwater gastrodermis gastrovascular genus hermaphrodites hydra hydroid hydrozoa hydrozoan hydrozoans macro medusa mesoglea microorganism microscope microscopy morphology nematocyst nematocysts obelia ovary phylum polyp predator regeneration reproduction science sessile small sticky structure symmetric tentacles zoology zooplankton