Hydra /ˈhaɪdrə/ is a genus of small,
fresh-water animals of the phylum Cnidaria and class Hydrozoa, native to
the temperate and tropical regions. Biologists are especially interested in Hydra because of their regenerative ability -- they appear .Sponges are animals of the phylum Porifera
(/pɒˈrɪfərə/; meaning "pore bearer"). They are multicellular organisms
that have bodies full of pores and channels allowing water to circulate
through them, consisting of jelly-like mesohyl sandwiched between two
thin layers of cells.ot to age or die of old age.