Hydras are classified under the phylum Cnidaria; some of its relatives are jellyfish and sea anemones. A hydra has many tentacles around the mouth opening.
Microorganisms & Protozoa
This page lists topics related to microorganisms and protozoa, including bacteria, unicellular protozoa, and multicellular pond life.
What is a Volvox? A quick overview Volvox is a genus of green algae. Volvoxes are free-floating single-cellular algae but typically stay together as spherical colonies (or balls) of 500-50,000 cells. They can live in a variety of freshwater habitats, including ponds, pools, and ditches. Under a microscope, volvoxes look like green marbles slowly rotating, …