Hydra are small multicellular organisms living in fresh water ponds. They are 1-3 mm in size and they feed on smaller waterfleas seen attached to one of the hydras tentracles. Hyrda have poisonous stinging tentacles (not harmful to people). They capture and swallow waterfleas whole. Hydra are used in research studies because these organisms do not age. Viewed with a combination of Polarized light and darkfield illumination at 25X.