The many minute aquatic creatures, such as protozoa and unicellular algae found in fresh water habitats(noun)
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Use "infusoria" in a sentence
"The microscope revealed the complexity of organic tissues, the existence of minute creatures, vaguely called infusoria, and the strange inhabitants of the blood, the red and white corpuscles."
"There are certain minute animal productions called infusoria and organisms peculiar to each portion of the globe."
"In 1838, Christian Gottfried Ehrenberg gave a description of the finer structure of the "infusoria" but it was Ferdinad Cohn, who in 1854 first ascertained with certainty that bacteria belonged to the vegetable kingdom."