||In`fu*so"ri*a (?), n. pl. [NL.; -- so
called because found in infusions which are left exposed to the air
for a time. See Infuse.] (Zoöl.) One of the
classes of Protozoa, including a large number of species, all of
minute size.
&fist; They are found in all seas, lakes, ponds, and streams, as
well as in infusions of organic matter exposed to the air. They are
distinguished by having vibrating lashes or cilia, with which they
obtain their food and swim about. They are devided into the orders
Flagellata, Ciliata, and Tentaculifera. See these words in the
Vocabulary.
Formely the term Infusoria was applied to all
microscopic organisms found in water, including many minute plants,
belonging to the diatoms, as well as minute animals belonging to
various classes, as the Rotifera, which are worms; and the Rhizopoda,
which constitute a distinct class of Protozoa. Fossil Infusoria are
mostly the siliceous shells of diatoms; sometimes they are siliceous
skeletons of Radiolaria, or the calcareous shells of
Foraminifera.
